Hoverfly response to spider webs in different light environments

Hoverfly response to spider webs in different light environments | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Hoverfly response to spider webs in different light environments Dulce Rodríguez-Morales, Horacio Tapia-McClung, Luis Robledo-Ospina, and 1 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-9216396/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted 6 You are reading this latest preprint version Abstract Sit and wait predators, such as orb web spiders, rely on their prey’s inability to detect them in order to make a successful catch. The spider web is a thin translucent structure that is coated with sticky glue droplets and helps in retaining flying insects once they collide with the web. Nevertheless, an approaching insect may still see and avoid the web under certain ambient conditions such as illumination. A web is more visible if the light from the sun is behind the web due to diffraction effects. Here we tested the effect of changing web appearance due to different light environments on the response of flying insects, using the orb web spider Allocyclosa bifurca as the predator and the hoverfly Sphaerophoria sp. as the prey. We photographed the webs under different light conditions using a multispectral camera and simulated their appearance from the perspective of hoverflies. We filmed the flights of approaching hoverflies and digitised their trajectories. Our results show that hoverflies can avoid spider webs irrespective of the light environment. Hoverflies approached as close as 5 cm before deviating away from the web suggesting that their flight control allows them to avoid predators successfully. insect vision flight dynamics predator-prey interactions spider webs Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Introduction In sit-and-wait predator systems, the likelihood of a prey being caught is dependent on the prey’s inability to detect the predator. Predators, therefore, have evolved multiple strategies to avoid being detected by their prey, the most important of which is crypsis (Ruxton et al. 2018 ). Here we refer to crypsis as an umbrella term encompassing several related concepts such as background matching, disruptive coloration and masquerade (Stevens 2013 ; Smith and Ruxton 2020 ). In this scenario, prey that approach too close to an undetected predator are caught. Sit and wait predators also can optimize their success by choosing sites with high traffic of potential prey, e.g., snakes that target sites with high frog abundance (Yang et al. 2024 ) or spiders exploiting the flower-pollinator relationship (Morse and Fritz 1982 ; Heiling et al. 2003 ; Rodríguez-Morales et al. 2021 ). Among spiders, there are two broad strategies: spiders that wait at flowers or other plant parts and ambush unsuspecting prey, and spiders that target flying insects by building webs to catch prey. In some cases, spiders may actively manipulate insects to approach them by the use of deceptive visual or chemical signals (Walter 2024 ; Warren and Severns 2024 ). In most cases, spiders depend on the lack of visibility of the web to avoid being detected. Spider webs, especially the orbicular ones, are generally composed of thin radial lines extending away from the hub and connected by spiral sticky silk. The entire structure is held in place with frame lines which in turn are attached to the substrate by means of anchor lines (Eberhard 1990 ). The visibility of webs can be affected by several factors. In rainy conditions, water droplets may accumulate on the webs, especially on the spirals, and cause the web to be more visible. This effect is also apparent in foggy or frosty conditions. Dust or pollen also may have a similar effect. Since orb web spiders usually rebuild their webs frequently, this enhanced visibility is a temporary problem but may last throughout the day potentially impacting insect interception. Visibility of the webs is also affected (in a few species) by the use of additional silk structures called decorations or stabilimenta which have been shown to be highly visible to potential insect prey due to their high ultraviolet reflectance (Craig and Bernard 1990 ; Walter 2024 ). However, studies have shown that stabilimenta may function as a prey attractant (by mimicking UV reflective floral guides) as well as a defense against predators, among other proposed functions (Eberhard 2020 ). Web visibility may also be affected by the color of the background; webs are more visible when seen against a dark background (e.g., forest undergrowth) in comparison to a lighter background (e.g., the sky). Other factors include density of the mesh, angle of the plane of the web, web structure, body coloration of the spider itself and ambient light conditions (Craig 1986 ; Craig 1988 ; Rößler et al. 2019 ). Spider webs are thin, generally colorless, and translucent structures that can interact with light in two ways: light can either reflect off the web strands or light can diffract by passing through the strands (Craig 2003 ). From the perspective of an observer, a spider web illuminated by sun rays behind the web is more visible due to the diffraction effect, whereas a web seen when the sun is overhead would be less visible because the sun rays would pass through the plane of the web and away from the observer’s eye. Webs in shaded areas are less visible. In an experiment conducted on orb web spiders in Panama (Craig 1988 ), where half the web was artificially made more reflective and the other half left untreated, it was shown that insects were significantly more likely to impact the untreated half than the reflective half. However, this study only counted web damage as indicators of prey impact and therefore there is no information on insects that may have approached webs but turned away without physical contact. Insect perception of spider webs has generally been measured through behavioral studies looking at holes caused by impacts, or by visual observations of impacts. In general, studies have often considered insect prey as interchangeable, without consideration of the difference in visual ability across species. Insects can see in color (Briscoe and Chittka 2001 ; Lunau 2014 ), but it is their visual acuity that allows them to detect and avoid obstacles (Land 1997 ; Cronin et al. 2014 ; Caves et al. 2018 ). For example, the dune wasp Microbembix nigrifrons can detect and respond to the presence of a cryptic crab spider Mecaphesa dubia at ~ 2 cm away (Rodríguez-Morales et al. 2021 ). The visual acuity of insects is mainly measured through anatomical measurements of the eyes and electrophysiological recordings in the optic lobe (Ryan et al. 2020 ), and recently a few studies have used a method of simulating the visual acuity using calibrated digital images (Caves and Johnsen 2017 ). Visual acuity is distance-dependent; insects can see objects with more details when they are closer. One of the few studies to consider the visual acuity of insects with respect to spider webs showed that insects can detect spider webs at distances ranging from 1.7 cm to 7.8 cm for Diptera flying towards webs of differing visibility. Web avoidance distance depended on the visual system of the insect species ( Drosophila vs mosquitos) and web density (Craig 1986 ). Insect interception of spider webs is also linked to their flight ability. Insects may detect the webs, but if they cannot control their flight and evade the obstacle in time, it would still lead to an impact. There is substantial variation among insects with respect to flight abilities (Taylor 2001 ); a hoverfly can reduce its speed dramatically and hover in the same spot in 3D space, whereas larger insects such as beetles may find it harder to maneuver in mid-air (Endo 1989 ). In this study, we addressed the effect of differential visibility of spider webs in relation to insect flight ability under semi-natural conditions. We placed orb webs in artificial frames and oriented them according to the position of the sun and filmed insect approaches in an outdoor setting. The frames were oriented such that approaching insects viewed the webs with the sun behind, sun in front, sun above and under shade, assuming a decreasing degree of visibility. Specifically, we asked the following questions: 1. Are there differences in the visibility of spider webs in different light conditions when seen from the perspective of potential prey such as hoverflies? 2. How do hoverflies interact with webs in different light environments? Methods Study Species We used the orb web spider Allocyclosa bifurca (Aranae: Araneidae) and the hoverfly Sphaerophoria sp. (Diptera: Syrphidae) for our experiments (Fig. 1 A,C). A. bifurca is distributed across North and Central America and the Antilles (Levi 1999 ). It builds small vertical orb webs, usually in front of walls or vegetation with broad leaves such as Agave. Sphaerophoria sp . feed on pollen and nectar and frequently encounter spiders as they forage (Yokoi and Fujisaki 2008 ). Experimental setup All experiments were carried out in a grass patch at the CCAD campus of the Universidad Veracruzana, Xalapa, Veracruz, Mexico. Spiders were kept in wooden boxes measuring 30 x 30 x 10 cm. Two sides of the box consisted of greased acrylic sheets to ensure that the webs were built in the center. The spiders were kept in these boxes until they had constructed a complete web. They were fed and watered every three days. Once the web was complete, it was transferred intact onto a 20 x 20 x 0.5 cm 3D-printed plastic frame (Fig. 1 B). The frames were dyed with a black matte paint to prevent light reflection, and small magnets were affixed to the bottom. The frames were then placed in position on the grass patch using nails driven into the ground. Webs were either with or without a spider. Light treatments were generated by positioning the web in the grass patch with the sun behind the web, sun in front of the web, sun above the web and under shade (created artificially with a large black shade cloth placed 2m above the web). We recorded hoverflies that flew towards the web and then assigned categories based on the direction of flight relative to the position of the sun. To quantify the visibility of the four treatments, four sample images were taken of webs in each light treatment. Using the Plot Profile tool in FIJI (Schindelin et al. 2012 ), we quantified the pixel intensity (a measure of how bright the pixels are, with black at 0 and white at 255) of the mean of 10 web strands (Supplementary Fig. S1 ). According to this, the treatments were organized in the following order from least to most visible: Shade, Sun above, Sun behind and Sun in front. Image acquisition To evaluate the influence of the light source direction on the web appearance as perceived by a hoverfly at different viewing distances, we used multispectral photos and visual modelling. The setup consisted of a Nikon D7100 camera converted to full-spectrum (modified by LifePixel.com), attached to a Jenoptik 105mm lens. We took two different types of photos using a Baader U filter (300–400 nm) and a Baader UV/IR Cut filter (400–700 nm) to obtain information on the ultraviolet (UV) and human visible parts of the light spectrum, respectively. The photos were taken between 11:00 and 14:00 hrs. using direct sunlight as the light source, and each photo included a scale bar and two Zenith sintered PTFE grey standards (70% and 10%) for photo calibration. Webs in frames were placed against a black background 1 m apart in different positions regarding the sun's position to illuminate the web and take the photos. We took photos with sunlight in front of the web, coming from behind, from above, and with the web placed in shade. Using the MICA toolbox (Troscianko and Stevens 2015 ), we merged the two types of photos to create a multispectral image that provided reflectance information in 5 channels: UV-blue, UV-red, blue, red, and green. Due to the lack of neurophysiologcial information about the inner color processing in the hoverfly visual system, we were unable to develop psychophysiological models to evaluate detectability. Instead, we created a putative visual system for modelling the hoverfly perception of the spider in its web using the available information for the vision parameters for the species Eristalis tenax spectral sensitivity (Horridge et al. 1975 ) with peaks at 330 (R7p), 340nm (R7y), 460nm, (R8p), 540nm (R8y), and 369nm (R1-6) and the standard daylight illuminant D65. We converted the multispectral images to quantum catch image based on this hoverfly visual system. Using the Quantitative Pattern Color Analysis (QCPA) framework (van den Berg et al. 2019 ), we applied an acuity correction using Gaussian convolution to simulate the visual acuity of E. tenax (1.8 cpd) (Straw et al. 2006 ; Feller et al. 2021 ). This allowed us to simulate the scene (i.e., the spider in its web) as perceived by an approaching hoverfly at different distances, i.e., 18, 6, and 2 cm. Finally, we created false color images for visualization purposes only, assigning the colors yellow, red, blue, and green to the photoreceptors R7p, R7y, R8p, and R8y, respectively. We ignored the photoreceptors R1-6 when assigning the colors to create the false color images because they are related to the achromatic mechanism of vision (Lunau 2014 ; An et al. 2018 ). Video acquisition and analysis We filmed hoverflies with a SONY FDR-AX700 video camera at 60 fps as they approached the web. The videos were taken with the camera looking downwards such that the web was in the central part of the filming area and a scale was visible (Fig. 2 A). Filming was done during the period of greatest activity of insects (09:00–14:00). To ensure that hoverflies were not avoiding the frame itself, we placed empty frames in the patch and observed instances (n = 12) where the insect went through the frame. The behavior of the hoverflies was evaluated by quantifying the number of events (impact or avoidance) as they approached the webs. To compare web identification and web contact under the light treatments; a Generalized Linear Model (GLM) was fitted to each of the response variables (identification and web contact). These analyses were conducted using JMP version 9 (JMP Statistical Discovery LLC, Cary, NC.). To track flight paths, videos where hoverflies approached the web were selected. Hoverflies trajectories were digitized by manual tracking using the MTrackJ plugin in FIJI (Schindelin et al. 2012 ). In each frame, the points of the head and the end of the abdomen were marked as well as the ends of the frame with the web (Fig. 2 B). Coordinates thus obtained were converted from pixel values to centimeters using the scale. Once the coordinates were obtained, we analyzed them in Mathematica ver 14.3. (WolframResearchInc 2024) using a custom written package. First, we visually identified the point where the hoverfly changes its trajectory and used this point to determine the decision distance. To compensate for observer biases, we used a subset of all the trajectories (n = 30) based on the criteria that there was a close interaction with the web: an approach, an avoidance, or an impact of the web. We selected the point of closest approach to the web plane and then selected all the points that appeared within a 6 cm radius from this point. These subsampled trajectories were then used for further analysis. From the trajectories, we calculated the persistence velocity of the hoverfly at each frame. Persistence velocity is a measure of the likelihood of the hoverfly continuing in the same path; it combines the speed of the hoverfly and the turning angles (Gurarie et al. 2009 ). The equation is as follows: Persistence Velocity ti = Velocity ti cos(Turning Angle ti ) Where ti refers to the i th frame in the video We plotted the persistence velocity values with distance from the web using a smooth density histogram. Persistence velocity values at or close to zero indicate that the hoverfly was either hovering or carrying out inspection behavior; positive values indicate the likelihood of the hoverfly proceeding in the same direction, and negative values indicate that the hoverfly was flying backwards. Here we considered values up to 10 cm/s as an indicator of web inspection. Analyses Visual modelling Hoverflies were more likely to detect the web at a closer distance (Fig. 2 ). However, we were unable to calculate metrics such as contrast between the web and the background due to the thinness of the silk. The sun behind treatment has high apparent detectability since the light passes through the translucent web and shows refraction patterns. These visual models suggest that webs are practically invisible to the visual system of a hoverfly under different light conditions until the fly is very close to the web or when there are light refractions. Behavior Across all experiments and irrespective of treatment, hoverflies hit the web only 7 times out of 30 encounters. None of them remained tangled in the web; all impacts were inconsequential and the flies managed to get away. Though flies were more likely to detect webs in the sun above treatment (Fig. 3 ), there was no significant difference in the hoverflies avoidance of the web with respect to the light treatment (Fisher exact probability test; p = 0.08), and hoverflies did not differ in their ability to avoid webs with spiders and webs without spiders (Fisher’s exact probability test; p = 0.31). The mean ± s.d distance at which the hoverflies detected the web was 2.05 ± 2.05 cm, but this distance was not affected by the light treatments (ANOVA; F 3,27 = 0.69, p = 0.56) Trajectory analyses Given that there was no significant difference in the behavior of the hoverflies with respect to the light treatment, we pooled all the data for the trajectory analysis. There were three types of turns observed during an interaction with the web, first a gradual turn where the hoverfly progressively changed direction, a sharp turn, where the hoverfly came almost to a stop before flying away and finally a mixed strategy where both gradual and sharp turns could be seen (Fig. 6 ). These interactions occurred without contact with the web. In other cases, the hoverfly either went through the web, possibly exploiting the gaps in the web near the edges of the frame, or hit the web briefly before bouncing back. With respect to the persistence velocity, there was a peak at around 5 cm away from the web (Fig. 7 A). Here, the data suggests that hoverflies did not make abrupt changes to their trajectory, since the peak corresponded to around 10 cm/s, which likely reflects detection and inspection of the web. A sample trajectory is shown in Fig. 7 B, where the inflection points (i.e., points where the hoverfly likely detected and responded to the presence of the web) are color coded according to the persistence values. Discussion Hoverflies could detect and avoid spider webs irrespective of the light treatments. Hoverflies performed this task of obstacle avoidance at very close distances (roughly 5 cm on average but sometimes as low as 1 cm), suggesting that their superior flight maneuverability is key in avoiding impact. This finding has profound implications for the visual ecology of predator-prey interactions especially with respect to spider webs. Due to the thinness of spider silk, it has long been assumed that spider webs are near undetectable to insects, irrespective of their flight style or visual system differences. The fact that some insects can see and avoid webs had long been noted (Lubin 1974 ; Nentwig 1987 ), but there is still little information on how frequently this occurs, especially under field conditions, and with emphasis on the identity of the insects (Eberhard 2020 ). Web interception has usually been estimated by counting damage made in the web, but this method is imprecise since it cannot distinguish between prey actually captured versus an insect that merely interacted with the web and subsequently escaped, nor can it account for interactions where the insect closely approached the web but then avoided impact (Eberhard 2020 ). Insects such as Drosophila can even distinguish and avoid low- and high-density webs, whereas mosquitos did not differentiate between these web types, but nevertheless avoided them (Craig 1986 ). These experiments were done in controlled conditions under artificial light but nevertheless indicate that the spatial resolving power of these insects is sufficient to detect what has been assumed to be at the limits of detection by an insect with compound eyes. Using webs with artificially enhanced visibility, and against a high contrast versus a low contrast background, the rate of insect impact was similar, suggesting that the different webs were treated similarly by insects (Craig 1988 ). Here the experiment was carried out in natural conditions but without any information on the identity of the insects that hit the web nor whether the impacts resulted in prey capture. How do insects detect obstacles? In our study, hoverflies were able to detect the web 2–5 cm away, as evidenced by the decision distance (Fig. 3 B) and the peak in persistence velocity values (Fig. 6 ). Most data on the flight of insects as they approach and avoid collisions comes from studies on bees. Bees use optic flow (i.e., the apparent motion of the immediate environment of the bee, generated by the bee’s own movement) to gauge their speed and distance from the obstacle, and regulate their flight accordingly (Egelhaaf et al. 2014 ). They have been shown to use the relative retinal expansion velocity, (a measure of the rate of change of apparent size of the obstacle) to initiate evasion (Ravi et al. 2022 ). Bumblebees in particular can evaluate the size of gaps in the vegetation in relation to their own body size to navigate through cluttered environments by manipulating their flight speed (Ravi et al. 2019 ). Most experiments use opaque obstacles such as dowels or walls, which would theoretically be easier to detect and avoid. But bees were even able to navigate through an experimental arena cluttered with transparent (to human eyes) obstacles without collisions and seemed to optimize their trajectories with experience (Jeschke et al. 2025 ). This process of using motion and vision together is termed Active Vision, briefly defined as a closed loop where animals can manipulate their visual input to enhance perception and consequently the decision-making process (MaBouDi et al. 2025 ). In the case of spider webs, detection may be possible due to the geometry of the entire web, with the radiating lines and spirals providing a more salient target rather than when faced with just a single line, but this idea remains to be tested. Furthermore, the type of flight employed by the insect would also influence detection. The flight mode of the insect, i.e., fast/direct, gradual/curved and slow/directionless flights, has been shown to directly affect the proportion of individuals that avoided orb webs (Endo 1989 ). The visual modelling approach using multispectral digital photography has many advantages; the foremost one is that it allows us to visualize an entire scene, in this case the spider web under different light conditions, from the perspective of the hoverfly. A more traditional method, such as a spectrometer to measure the reflectance spectra of the webs, would not work here because these measurements are done independent of ambient light and focus on selected points. However, there are important caveats of the efficacy of this method. Firstly, there is a lack of data on the visual acuity of most species of interest, and we often have to use the taxonomically closest option, which may not be sufficient, especially given the immense variation in insect eyes, sometimes even within the same spaces (Straw et al. 2006 ). Secondly, these measurements are made of a static image taken perpendicularly to the plane of the web. As noted above, insects are constantly in motion and may approach webs at any angle, which would change the view of the web (Eberhard 2020 ). Hoverflies rely on their visual ability in several contexts, ranging from interspecific contests such as chasing behavior (Collett and Land 1978 ), mating behavior (Collett and Land 1975 ), detecting the approach of flying predators such as wasps (Thyselius et al. 2018 ) and identifying suitable flowers to forage on (An et al. 2018 ). Motion cues in particular are more relevant to detection and perception, and insects can augment their detection of obstacles or predators by the sidewise movement of the entire body (saccades, e.g., hoverflies that detect a crab spider on a flower (Yokoi and Fujisaki 2008 ), or through head stabilization (Collett and Land 1975 ; Egelhaaf 2012 ). Furthermore, a recent study in Drosophila showed that there are ultrafast photomechanical movements at the level of photoreceptors which significantly enhance the insect’s ability to process spatial information (Juusola et al. 2025 ). Given that insects can detect and avoid spider webs, the question of how spiders trap insects becomes more relevant. Spider webs have long been considered as passive sieves, but that view is changing. Spiders can deform the plane of the web such that insects do not get a complete view as they approach (Craig 2003 ). Furthermore, spiders are generalist predators and do not depend on any one species of insect for sustenance (Nentwig 1985 ). They can survive easily up to a week without prey and are accustomed to hunger (Nakamura 1987 ). From the spider’s perspective, all it needs is a few individuals that fail to detect the web. This can be achieved when considering that individual insects alter their flight speed and mode almost constantly. A bee flying faster on its way back to the hive should have a harder time detecting a web than one that is foraging slowly among the vegetation (Rao et al. 2008 ). Further research on quantifying and comparing the flight trajectories of insects that avoid the web versus those that are caught will lead to a more complete understanding of this interaction. Declarations Acknowledgments We thank Derian Jaime Duran and Carlos Villa del Carmen for help in tracking the insect flights. 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Sci Rep 11:15442. https://doi.org/10.1038/s41598-021-94926-7 Rößler DC, Ogan S, Curio E, Krehenwinkel H (2019) Ability makes a thief: vision, learning, and swift escape help kleptoparasitic hover wasps not to fall prey to their spider hosts. Behav Ecol Sociobiol 73:152. https://doi.org/10.1007/s00265-019-2767-8 Ruxton G, Sherratt TN, Speed M (2018) Avoiding attack: the evolutionary ecology of crypsis, warning signals and mimicry, 2nd edn. Oxford University Press, Oxford (UK) Ryan LA, Cunningham R, Hart NS, Ogawa Y (2020) The buzz around spatial resolving power and contrast sensitivity in the honeybee, Apis mellifera . Vis Res 169:25–32. https://doi.org/10.1016/j.visres.2020.02.005 Schindelin J, Arganda-Carreras I, Frise E, Kaynig V, Longair M, Pietzsch T, Preibisch S, Rueden C, Saalfeld S, Schmid B et al (2012) Fiji: an open-source platform for biological-image analysis. Nat Methods 9:676–682. https://doi.org/10.1038/nmeth.2019 Smith MQRP, Ruxton GD (2020) Camouflage in predators. Biol Rev 95:1325–1340. https://doi.org/10.1111/brv.12612 Stevens M (2013) Sensory ecology, behaviour, and evolution, 1st edn. Oxford University Press, Oxford (UK) Straw AD, Warrant EJ, O'Carroll DC (2006) A 'bright zone' in male hoverfly ( Eristalis tenax ) eyes and associated faster motion detection and increased contrast sensitivity. J Exp Biol 209:4339–4354. https://doi.org/10.1242/jeb.02517 Taylor GK (2001) Mechanics and aerodynamics of insect flight control. Biol Rev 76:449–471. https://doi.org/10.1017/s1464793101005759 Thyselius M, Gonzalez-Bellido PT, Wardill TJ, Nordström K (2018) Visual approach computation in feeding hoverflies. J Exp Biol 221:jeb177162. https://doi.org/10.1242/jeb.177162 Troscianko J, Stevens M (2015) Image calibration and analysis toolbox – a free software suite for objectively measuring reflectance, colour and pattern. Methods Ecol Evol 6:1320–1331. https://doi.org/10.1111/2041-210x.12439 van den Berg CP, Troscianko J, Endler JA, Marshall NJ, Cheney KL (2019) Quantitative colour pattern analysis (QCPA): a comprehensive framework for the analysis of colour patterns in nature. Methods Ecol Evol 11:316–332. https://doi.org/10.1111/2041-210x.13328 Walter A (2024) The function of web decorations in orb web spiders. Front Arachn Sci 3:1384128. https://doi.org/10.3389/frchs.2024.1384128 Warren AD, Severns PM (2024) Fatal attraction: Argiope spiders lure male Hemileuca moth prey with the promise of sex. Insects 15:53. https://doi.org/10.3390/insects15010053 Wolfram Research Inc (2024) Mathematica Ver 14.3. Champaign (IL): Wolfram Research. https://www.wolfram.com/mathematica Yang C-K, Yang Y-J, Mori A (2024) Ambush site selection by a green bamboo pit viper: relation to prey abundance and comparison between juveniles and adults. Zool Stud 63:e55. https://doi.org/10.6620/zs.2024.63-55 Yokoi T, Fujisaki K (2008) Hesitation behaviour of hoverflies Sphaerophoria spp. to avoid ambush by crab spiders. Naturwissenschaften 96:195–200. https://doi.org/10.1007/s00114-008-0459-8 Additional Declarations No competing interests reported. Supplementary Files S1treatmentvisibility.pdf S2SampleVideo.mp4 Cite Share Download PDF Status: Under Review Version 1 posted Reviews received at journal 26 Apr, 2026 Reviewers agreed at journal 20 Apr, 2026 Reviewers invited by journal 20 Apr, 2026 Editor assigned by journal 31 Mar, 2026 Submission checks completed at journal 31 Mar, 2026 First submitted to journal 24 Mar, 2026 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-9216396","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":629768512,"identity":"fd94bdbf-557f-431e-adde-7fa6e438ccb1","order_by":0,"name":"Dulce Rodríguez-Morales","email":"","orcid":"","institution":"Universidad Veracruzana","correspondingAuthor":false,"prefix":"","firstName":"Dulce","middleName":"","lastName":"Rodríguez-Morales","suffix":""},{"id":629768513,"identity":"0cf486b1-3953-4b74-b9c4-dcad9039b21a","order_by":1,"name":"Horacio Tapia-McClung","email":"","orcid":"","institution":"Universidad Veracruzana","correspondingAuthor":false,"prefix":"","firstName":"Horacio","middleName":"","lastName":"Tapia-McClung","suffix":""},{"id":629768514,"identity":"6f94e04e-d6b6-405b-83d7-18f9d9ee96dc","order_by":2,"name":"Luis Robledo-Ospina","email":"","orcid":"","institution":"Universidad Veracruzana","correspondingAuthor":false,"prefix":"","firstName":"Luis","middleName":"","lastName":"Robledo-Ospina","suffix":""},{"id":629768515,"identity":"46726214-d057-4b40-a0c7-9f6da2e1b7cb","order_by":3,"name":"Dinesh Rao","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAg0lEQVRIiWNgGAWjYLCCDyTrYJxBshZmHpKUG9w+/PCxbdthBt0ZCcRqOZdmbJwL1GJ25gCRWiR7GMykc9vSGMyONxCthf2btCVIy2EidTDw8/CYSTO22ZBgC1BLsWHPORse4v3CxsO+8cGPMgk5sxsJxLoMCkiLmlEwCkbBKBgFBAAAlsIgbghFNB0AAAAASUVORK5CYII=","orcid":"","institution":"Universidad Veracruzana","correspondingAuthor":true,"prefix":"","firstName":"Dinesh","middleName":"","lastName":"Rao","suffix":""}],"badges":[],"createdAt":"2026-03-24 22:53:41","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-9216396/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-9216396/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":108181443,"identity":"8378691f-1af7-4ead-b914-45e72565ae84","added_by":"auto","created_at":"2026-04-30 08:58:39","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":70848,"visible":true,"origin":"","legend":"\u003cp\u003eStudy species and web; A: \u003cem\u003eAllocyclosa bifurca\u003c/em\u003e, shown here with eggsac, B: Full orb web in a 3D printed frame as used in the experiments, C: the hoverfly \u003cem\u003eSphaerophoria sp\u003c/em\u003e.\u003c/p\u003e","description":"","filename":"image1.png","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/dc5c8bb1fd5ba4bb20231aef.png"},{"id":108181449,"identity":"dfbc384f-5303-4561-a3a9-31a9d065db74","added_by":"auto","created_at":"2026-04-30 08:58:39","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":145480,"visible":true,"origin":"","legend":"\u003cp\u003eWeb false color and acuity with sensitivity.\u003c/p\u003e\n\u003cp\u003eFalse color images modelling a putative hoverfly visual system, created from published data of spectral sensitivity and visual acuity (\u003cem\u003eEristalis tenax\u003c/em\u003e). The images simulate the approaching hoverfly point of view at different distances (2, 6, and 18 cm) of an \u003cem\u003eAllocyclosa bifurca\u003c/em\u003e spider in its web with the light source (sunlight) coming from different directions: from behind the web, from the front, with the sun in the zenith (above) and with the web under shade. Note that details of the web are harder to discern from a greater distance.\u003c/p\u003e","description":"","filename":"image2.png","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/4ea9156e5458d183d1fc8968.png"},{"id":108181750,"identity":"a4d631be-3ba9-4257-b4b2-3b9b21d30793","added_by":"auto","created_at":"2026-04-30 08:58:53","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":49576,"visible":true,"origin":"","legend":"\u003cp\u003eBehavior results. A: Webs were generally more often detected in the Sun Above and Shade treatments, but there was no difference in impacts across treatments. B: There was no significant difference in the distances at which the hoverflies changed their trajectories in the four light treatments.\u003c/p\u003e","description":"","filename":"image3.png","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/9ae08d3c8c85365557c4ad2d.png"},{"id":108182105,"identity":"1ece8dba-3d38-4aad-82f4-c4396a349ebe","added_by":"auto","created_at":"2026-04-30 08:59:09","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":108502,"visible":true,"origin":"","legend":"\u003cp\u003eA. Screen capture of the filming setup as seen from the top with the digitized flight trajectory overlaid and B. Sample trajectory. The position of the hoverfly is depicted with a black disk as the head and an orange line representing the body axis. The red dashed line is the web. The trajectory starts at the bottom left. The arrows at \u003cstrong\u003ea\u003c/strong\u003e and \u003cstrong\u003eb\u003c/strong\u003e show points of detection and impact respectively.\u003c/p\u003e","description":"","filename":"image4.png","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/83ff6ce98d47971a1ae518fd.png"},{"id":108490984,"identity":"e1e09037-8d40-46d9-b97b-9092a6ddd0bd","added_by":"auto","created_at":"2026-05-05 09:50:46","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":102637,"visible":true,"origin":"","legend":"\u003cp\u003eSample trajectory with all parameters. A. Full trajectory of a hoverfly approaching the web and then moving away. The position of the hoverfly is depicted with a black disk as the head and an orange line representing the body axis. The red dashed line is the web frame (20 cm). B. The sub sampled trajectory segmented according to a possible range of interaction, i.e., within 6 cm of the closest point on the web. C. The subsampled trajectory with the head of the hoverfly color coded according to its speed. D. The subsampled trajectory color coded according to its persistence velocity values (see Methods for details). Note that these values are lower during the approach and higher while avoiding the web.\u003c/p\u003e","description":"","filename":"image5.png","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/4df751876c042fdabe2279b2.png"},{"id":108490901,"identity":"ee817d1e-c83c-4e96-936d-dcd8bf35cea8","added_by":"auto","created_at":"2026-05-05 09:49:41","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":23962,"visible":true,"origin":"","legend":"\u003cp\u003eSome examples of hoverfly flight turns and web interactions identified in the study. The web is shown as a red dashed line.\u003c/p\u003e","description":"","filename":"image6.png","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/2eb3d29b132e4fa9a82e4542.png"},{"id":108181757,"identity":"06b17cfc-7980-4a57-9d98-6cfbe8d298af","added_by":"auto","created_at":"2026-04-30 08:58:53","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":59573,"visible":true,"origin":"","legend":"\u003cp\u003eA. Persistence velocity of hoverflies with respect to distance from the web. A peak of persistence velocity values was seen at around 5 cm from the web, suggesting that hoverflies generally detect and respond to the web at this distance. B. A sample trajectory color coded according to the persistence velocity values, arrows indicate potential inflection points in the flight. The web is shown as a red dashed line, with 20 cm length.\u003c/p\u003e","description":"","filename":"image7.png","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/c4fb627c58daf32ec90c8291.png"},{"id":108804581,"identity":"b91f57ac-f266-4501-83ba-25a82c4c95a7","added_by":"auto","created_at":"2026-05-08 15:21:45","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":811692,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/8cfba923-5648-485e-bdc4-80fa0b4ca7cb.pdf"},{"id":108111621,"identity":"a050d985-8333-4109-9390-1d153ad8d6d1","added_by":"auto","created_at":"2026-04-29 13:01:35","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":206012,"visible":true,"origin":"","legend":"","description":"","filename":"S1treatmentvisibility.pdf","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/a652106f9ee8e6ea37816dcb.pdf"},{"id":108182504,"identity":"45f77f13-fc2a-4d82-93c2-6a7b96f7d061","added_by":"auto","created_at":"2026-04-30 08:59:24","extension":"mp4","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":25307619,"visible":true,"origin":"","legend":"","description":"","filename":"S2SampleVideo.mp4","url":"https://assets-eu.researchsquare.com/files/rs-9216396/v1/c3105e6d3f86ffcc43b91324.mp4"}],"financialInterests":"No competing interests reported.","formattedTitle":"Hoverfly response to spider webs in different light environments","fulltext":[{"header":"Introduction","content":"\u003cp\u003eIn sit-and-wait predator systems, the likelihood of a prey being caught is dependent on the prey\u0026rsquo;s inability to detect the predator. Predators, therefore, have evolved multiple strategies to avoid being detected by their prey, the most important of which is crypsis (Ruxton et al. \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Here we refer to crypsis as an umbrella term encompassing several related concepts such as background matching, disruptive coloration and masquerade (Stevens \u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e2013\u003c/span\u003e; Smith and Ruxton \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). In this scenario, prey that approach too close to an undetected predator are caught. Sit and wait predators also can optimize their success by choosing sites with high traffic of potential prey, e.g., snakes that target sites with high frog abundance (Yang et al. \u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e2024\u003c/span\u003e) or spiders exploiting the flower-pollinator relationship (Morse and Fritz \u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e1982\u003c/span\u003e; Heiling et al. \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e2003\u003c/span\u003e; Rodr\u0026iacute;guez-Morales et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eAmong spiders, there are two broad strategies: spiders that wait at flowers or other plant parts and ambush unsuspecting prey, and spiders that target flying insects by building webs to catch prey. In some cases, spiders may actively manipulate insects to approach them by the use of deceptive visual or chemical signals (Walter \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2024\u003c/span\u003e; Warren and Severns \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). In most cases, spiders depend on the lack of visibility of the web to avoid being detected. Spider webs, especially the orbicular ones, are generally composed of thin radial lines extending away from the hub and connected by spiral sticky silk. The entire structure is held in place with frame lines which in turn are attached to the substrate by means of anchor lines (Eberhard \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e1990\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe visibility of webs can be affected by several factors. In rainy conditions, water droplets may accumulate on the webs, especially on the spirals, and cause the web to be more visible. This effect is also apparent in foggy or frosty conditions. Dust or pollen also may have a similar effect. Since orb web spiders usually rebuild their webs frequently, this enhanced visibility is a temporary problem but may last throughout the day potentially impacting insect interception. Visibility of the webs is also affected (in a few species) by the use of additional silk structures called decorations or stabilimenta which have been shown to be highly visible to potential insect prey due to their high ultraviolet reflectance (Craig and Bernard \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e1990\u003c/span\u003e; Walter \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e2024\u003c/span\u003e). However, studies have shown that stabilimenta may function as a prey attractant (by mimicking UV reflective floral guides) as well as a defense against predators, among other proposed functions (Eberhard \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Web visibility may also be affected by the color of the background; webs are more visible when seen against a dark background (e.g., forest undergrowth) in comparison to a lighter background (e.g., the sky). Other factors include density of the mesh, angle of the plane of the web, web structure, body coloration of the spider itself and ambient light conditions (Craig \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1986\u003c/span\u003e; Craig \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1988\u003c/span\u003e; R\u0026ouml;\u0026szlig;ler et al. \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e2019\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eSpider webs are thin, generally colorless, and translucent structures that can interact with light in two ways: light can either reflect off the web strands or light can diffract by passing through the strands (Craig \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). From the perspective of an observer, a spider web illuminated by sun rays behind the web is more visible due to the diffraction effect, whereas a web seen when the sun is overhead would be less visible because the sun rays would pass through the plane of the web and away from the observer\u0026rsquo;s eye. Webs in shaded areas are less visible. In an experiment conducted on orb web spiders in Panama (Craig \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1988\u003c/span\u003e), where half the web was artificially made more reflective and the other half left untreated, it was shown that insects were significantly more likely to impact the untreated half than the reflective half. However, this study only counted web damage as indicators of prey impact and therefore there is no information on insects that may have approached webs but turned away without physical contact.\u003c/p\u003e \u003cp\u003eInsect perception of spider webs has generally been measured through behavioral studies looking at holes caused by impacts, or by visual observations of impacts. In general, studies have often considered insect prey as interchangeable, without consideration of the difference in visual ability across species. Insects can see in color (Briscoe and Chittka \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2001\u003c/span\u003e; Lunau \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e2014\u003c/span\u003e), but it is their visual acuity that allows them to detect and avoid obstacles (Land \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e1997\u003c/span\u003e; Cronin et al. \u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e2014\u003c/span\u003e; Caves et al. \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). For example, the dune wasp \u003cem\u003eMicrobembix nigrifrons\u003c/em\u003e can detect and respond to the presence of a cryptic crab spider \u003cem\u003eMecaphesa dubia\u003c/em\u003e at ~\u0026thinsp;2 cm away (Rodr\u0026iacute;guez-Morales et al. \u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e2021\u003c/span\u003e). The visual acuity of insects is mainly measured through anatomical measurements of the eyes and electrophysiological recordings in the optic lobe (Ryan et al. \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e2020\u003c/span\u003e), and recently a few studies have used a method of simulating the visual acuity using calibrated digital images (Caves and Johnsen \u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e2017\u003c/span\u003e). Visual acuity is distance-dependent; insects can see objects with more details when they are closer. One of the few studies to consider the visual acuity of insects with respect to spider webs showed that insects can detect spider webs at distances ranging from 1.7 cm to 7.8 cm for Diptera flying towards webs of differing visibility. Web avoidance distance depended on the visual system of the insect species (\u003cem\u003eDrosophila\u003c/em\u003e vs mosquitos) and web density (Craig \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1986\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eInsect interception of spider webs is also linked to their flight ability. Insects may detect the webs, but if they cannot control their flight and evade the obstacle in time, it would still lead to an impact. There is substantial variation among insects with respect to flight abilities (Taylor \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e2001\u003c/span\u003e); a hoverfly can reduce its speed dramatically and hover in the same spot in 3D space, whereas larger insects such as beetles may find it harder to maneuver in mid-air (Endo \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1989\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eIn this study, we addressed the effect of differential visibility of spider webs in relation to insect flight ability under semi-natural conditions. We placed orb webs in artificial frames and oriented them according to the position of the sun and filmed insect approaches in an outdoor setting. The frames were oriented such that approaching insects viewed the webs with the sun behind, sun in front, sun above and under shade, assuming a decreasing degree of visibility. Specifically, we asked the following questions:\u003c/p\u003e \u003cp\u003e\u003cspan\u003e1. Are there differences in the visibility of spider webs in different light conditions when seen from the perspective of potential prey such as hoverflies?\u003cbr\u003e\u003c/span\u003e\u003cspan\u003e2. How do hoverflies interact with webs in different light environments?\u003cbr\u003e\u003c/span\u003e\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003eStudy Species\u003c/p\u003e \u003cp\u003eWe used the orb web spider \u003cem\u003eAllocyclosa bifurca\u003c/em\u003e (Aranae: Araneidae) and the hoverfly \u003cem\u003eSphaerophoria\u003c/em\u003e sp. (Diptera: Syrphidae) for our experiments (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eA,C). \u003cem\u003eA. bifurca\u003c/em\u003e is distributed across North and Central America and the Antilles (Levi \u003cspan class=\"CitationRef\"\u003e1999\u003c/span\u003e). It builds small vertical orb webs, usually in front of walls or vegetation with broad leaves such as Agave. \u003cem\u003eSphaerophoria sp\u003c/em\u003e. feed on pollen and nectar and frequently encounter spiders as they forage (Yokoi and Fujisaki \u003cspan class=\"CitationRef\"\u003e2008\u003c/span\u003e).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eExperimental setup\u003c/p\u003e \u003cp\u003eAll experiments were carried out in a grass patch at the CCAD campus of the Universidad Veracruzana, Xalapa, Veracruz, Mexico. Spiders were kept in wooden boxes measuring 30 x 30 x 10 cm. Two sides of the box consisted of greased acrylic sheets to ensure that the webs were built in the center. The spiders were kept in these boxes until they had constructed a complete web. They were fed and watered every three days. Once the web was complete, it was transferred intact onto a 20 x 20 x 0.5 cm 3D-printed plastic frame (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003eB). The frames were dyed with a black matte paint to prevent light reflection, and small magnets were affixed to the bottom. The frames were then placed in position on the grass patch using nails driven into the ground. Webs were either with or without a spider. Light treatments were generated by positioning the web in the grass patch with the sun behind the web, sun in front of the web, sun above the web and under shade (created artificially with a large black shade cloth placed 2m above the web). We recorded hoverflies that flew towards the web and then assigned categories based on the direction of flight relative to the position of the sun.\u003c/p\u003e \u003cp\u003eTo quantify the visibility of the four treatments, four sample images were taken of webs in each light treatment. Using the Plot Profile tool in FIJI (Schindelin et al. \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e), we quantified the pixel intensity (a measure of how bright the pixels are, with black at 0 and white at 255) of the mean of 10 web strands (Supplementary Fig. \u003cspan class=\"InternalRef\"\u003eS1\u003c/span\u003e). According to this, the treatments were organized in the following order from least to most visible: Shade, Sun above, Sun behind and Sun in front.\u003c/p\u003e \u003cp\u003eImage acquisition\u003c/p\u003e \u003cp\u003eTo evaluate the influence of the light source direction on the web appearance as perceived by a hoverfly at different viewing distances, we used multispectral photos and visual modelling. The setup consisted of a Nikon D7100 camera converted to full-spectrum (modified by LifePixel.com), attached to a Jenoptik 105mm lens. We took two different types of photos using a Baader U filter (300–400 nm) and a Baader UV/IR Cut filter (400–700 nm) to obtain information on the ultraviolet (UV) and human visible parts of the light spectrum, respectively. The photos were taken between 11:00 and 14:00 hrs. using direct sunlight as the light source, and each photo included a scale bar and two Zenith sintered PTFE grey standards (70% and 10%) for photo calibration.\u003c/p\u003e \u003cp\u003eWebs in frames were placed against a black background 1 m apart in different positions regarding the sun's position to illuminate the web and take the photos. We took photos with sunlight in front of the web, coming from behind, from above, and with the web placed in shade.\u003c/p\u003e \u003cp\u003eUsing the MICA toolbox (Troscianko and Stevens \u003cspan class=\"CitationRef\"\u003e2015\u003c/span\u003e), we merged the two types of photos to create a multispectral image that provided reflectance information in 5 channels: UV-blue, UV-red, blue, red, and green. Due to the lack of neurophysiologcial information about the inner color processing in the hoverfly visual system, we were unable to develop psychophysiological models to evaluate detectability. Instead, we created a putative visual system for modelling the hoverfly perception of the spider in its web using the available information for the vision parameters for the species \u003cem\u003eEristalis tenax\u003c/em\u003e spectral sensitivity (Horridge et al. \u003cspan class=\"CitationRef\"\u003e1975\u003c/span\u003e) with peaks at 330 (R7p), 340nm (R7y), 460nm, (R8p), 540nm (R8y), and 369nm (R1-6) and the standard daylight illuminant D65. We converted the multispectral images to quantum catch image based on this hoverfly visual system.\u003c/p\u003e \u003cp\u003eUsing the Quantitative Pattern Color Analysis (QCPA) framework (van den Berg et al. \u003cspan class=\"CitationRef\"\u003e2019\u003c/span\u003e), we applied an acuity correction using Gaussian convolution to simulate the visual acuity of \u003cem\u003eE. tenax\u003c/em\u003e (1.8 cpd) (Straw et al. \u003cspan class=\"CitationRef\"\u003e2006\u003c/span\u003e; Feller et al. \u003cspan class=\"CitationRef\"\u003e2021\u003c/span\u003e). This allowed us to simulate the scene (i.e., the spider in its web) as perceived by an approaching hoverfly at different distances, i.e., 18, 6, and 2 cm. Finally, we created false color images for visualization purposes only, assigning the colors yellow, red, blue, and green to the photoreceptors R7p, R7y, R8p, and R8y, respectively. We ignored the photoreceptors R1-6 when assigning the colors to create the false color images because they are related to the achromatic mechanism of vision (Lunau \u003cspan class=\"CitationRef\"\u003e2014\u003c/span\u003e; An et al. \u003cspan class=\"CitationRef\"\u003e2018\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eVideo acquisition and analysis\u003c/p\u003e \u003cp\u003eWe filmed hoverflies with a SONY FDR-AX700 video camera at 60 fps as they approached the web. The videos were taken with the camera looking downwards such that the web was in the central part of the filming area and a scale was visible (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eA). Filming was done during the period of greatest activity of insects (09:00–14:00). To ensure that hoverflies were not avoiding the frame itself, we placed empty frames in the patch and observed instances (n = 12) where the insect went through the frame. The behavior of the hoverflies was evaluated by quantifying the number of events (impact or avoidance) as they approached the webs. To compare web identification and web contact under the light treatments; a Generalized Linear Model (GLM) was fitted to each of the response variables (identification and web contact). These analyses were conducted using JMP version 9 (JMP Statistical Discovery LLC, Cary, NC.).\u003c/p\u003e \u003cp\u003e \u003c/p\u003e \u003cp\u003eTo track flight paths, videos where hoverflies approached the web were selected. Hoverflies trajectories were digitized by manual tracking using the MTrackJ plugin in FIJI (Schindelin et al. \u003cspan class=\"CitationRef\"\u003e2012\u003c/span\u003e). In each frame, the points of the head and the end of the abdomen were marked as well as the ends of the frame with the web (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003eB). Coordinates thus obtained were converted from pixel values to centimeters using the scale. Once the coordinates were obtained, we analyzed them in Mathematica ver 14.3. (WolframResearchInc 2024) using a custom written package.\u003c/p\u003e \u003cp\u003eFirst, we visually identified the point where the hoverfly changes its trajectory and used this point to determine the decision distance. To compensate for observer biases, we used a subset of all the trajectories (n = 30) based on the criteria that there was a close interaction with the web: an approach, an avoidance, or an impact of the web. We selected the point of closest approach to the web plane and then selected all the points that appeared within a 6 cm radius from this point. These subsampled trajectories were then used for further analysis.\u003c/p\u003e \u003cp\u003eFrom the trajectories, we calculated the persistence velocity of the hoverfly at each frame. Persistence velocity is a measure of the likelihood of the hoverfly continuing in the same path; it combines the speed of the hoverfly and the turning angles (Gurarie et al. \u003cspan class=\"CitationRef\"\u003e2009\u003c/span\u003e). The equation is as follows:\u003c/p\u003e \u003cp\u003ePersistence Velocity\u003csub\u003e\u003cem\u003eti\u003c/em\u003e\u003c/sub\u003e= Velocity\u003csub\u003e\u003cem\u003eti\u003c/em\u003e\u003c/sub\u003e cos(Turning Angle\u003csub\u003e\u003cem\u003eti\u003c/em\u003e\u003c/sub\u003e)\u003c/p\u003e \u003cp\u003eWhere \u003cem\u003eti\u003c/em\u003e refers to the \u003cem\u003ei\u003c/em\u003e\u003csup\u003eth\u003c/sup\u003e frame in the video\u003c/p\u003e \u003cp\u003eWe plotted the persistence velocity values with distance from the web using a smooth density histogram. Persistence velocity values at or close to zero indicate that the hoverfly was either hovering or carrying out inspection behavior; positive values indicate the likelihood of the hoverfly proceeding in the same direction, and negative values indicate that the hoverfly was flying backwards. Here we considered values up to 10 cm/s as an indicator of web inspection.\u003c/p\u003e "},{"header":"Analyses","content":"\u003cp\u003eVisual modelling\u003c/p\u003e\u003cp\u003eHoverflies were more likely to detect the web at a closer distance (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e). However, we were unable to calculate metrics such as contrast between the web and the background due to the thinness of the silk. The sun behind treatment has high apparent detectability since the light passes through the translucent web and shows refraction patterns. These visual models suggest that webs are practically invisible to the visual system of a hoverfly under different light conditions until the fly is very close to the web or when there are light refractions.\u003c/p\u003e\u003cp\u003eBehavior\u003c/p\u003e\u003cp\u003eAcross all experiments and irrespective of treatment, hoverflies hit the web only 7 times out of 30 encounters. None of them remained tangled in the web; all impacts were inconsequential and the flies managed to get away. Though flies were more likely to detect webs in the sun above treatment (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e), there was no significant difference in the hoverflies avoidance of the web with respect to the light treatment (Fisher exact probability test; p = 0.08), and hoverflies did not differ in their ability to avoid webs with spiders and webs without spiders (Fisher’s exact probability test; p = 0.31). The mean ± s.d distance at which the hoverflies detected the web was 2.05 ± 2.05 cm, but this distance was not affected by the light treatments (ANOVA; F\u003csub\u003e3,27\u003c/sub\u003e = 0.69, p = 0.56)\u003c/p\u003e\u003cp\u003eTrajectory analyses\u003c/p\u003e\u003cp\u003eGiven that there was no significant difference in the behavior of the hoverflies with respect to the light treatment, we pooled all the data for the trajectory analysis. There were three types of turns observed during an interaction with the web, first a gradual turn where the hoverfly progressively changed direction, a sharp turn, where the hoverfly came almost to a stop before flying away and finally a mixed strategy where both gradual and sharp turns could be seen (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e6\u003c/span\u003e). These interactions occurred without contact with the web. In other cases, the hoverfly either went through the web, possibly exploiting the gaps in the web near the edges of the frame, or hit the web briefly before bouncing back. With respect to the persistence velocity, there was a peak at around 5 cm away from the web (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eA). Here, the data suggests that hoverflies did not make abrupt changes to their trajectory, since the peak corresponded to around 10 cm/s, which likely reflects detection and inspection of the web. A sample trajectory is shown in Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e7\u003c/span\u003eB, where the inflection points (i.e., points where the hoverfly likely detected and responded to the presence of the web) are color coded according to the persistence values.\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eHoverflies could detect and avoid spider webs irrespective of the light treatments. Hoverflies performed this task of obstacle avoidance at very close distances (roughly 5 cm on average but sometimes as low as 1 cm), suggesting that their superior flight maneuverability is key in avoiding impact. This finding has profound implications for the visual ecology of predator-prey interactions especially with respect to spider webs. Due to the thinness of spider silk, it has long been assumed that spider webs are near undetectable to insects, irrespective of their flight style or visual system differences. The fact that some insects can see and avoid webs had long been noted (Lubin \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e1974\u003c/span\u003e; Nentwig \u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e1987\u003c/span\u003e), but there is still little information on how frequently this occurs, especially under field conditions, and with emphasis on the identity of the insects (Eberhard \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e). Web interception has usually been estimated by counting damage made in the web, but this method is imprecise since it cannot distinguish between prey actually captured versus an insect that merely interacted with the web and subsequently escaped, nor can it account for interactions where the insect closely approached the web but then avoided impact (Eberhard \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eInsects such as \u003cem\u003eDrosophila\u003c/em\u003e can even distinguish and avoid low- and high-density webs, whereas mosquitos did not differentiate between these web types, but nevertheless avoided them (Craig \u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e1986\u003c/span\u003e). These experiments were done in controlled conditions under artificial light but nevertheless indicate that the spatial resolving power of these insects is sufficient to detect what has been assumed to be at the limits of detection by an insect with compound eyes. Using webs with artificially enhanced visibility, and against a high contrast versus a low contrast background, the rate of insect impact was similar, suggesting that the different webs were treated similarly by insects (Craig \u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e1988\u003c/span\u003e). Here the experiment was carried out in natural conditions but without any information on the identity of the insects that hit the web nor whether the impacts resulted in prey capture.\u003c/p\u003e \u003cp\u003eHow do insects detect obstacles? In our study, hoverflies were able to detect the web 2\u0026ndash;5 cm away, as evidenced by the decision distance (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eB) and the peak in persistence velocity values (Fig.\u0026nbsp;\u003cspan refid=\"Fig6\" class=\"InternalRef\"\u003e6\u003c/span\u003e). Most data on the flight of insects as they approach and avoid collisions comes from studies on bees. Bees use optic flow (i.e., the apparent motion of the immediate environment of the bee, generated by the bee\u0026rsquo;s own movement) to gauge their speed and distance from the obstacle, and regulate their flight accordingly (Egelhaaf et al. \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e2014\u003c/span\u003e). They have been shown to use the relative retinal expansion velocity, (a measure of the rate of change of apparent size of the obstacle) to initiate evasion (Ravi et al. \u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e2022\u003c/span\u003e). Bumblebees in particular can evaluate the size of gaps in the vegetation in relation to their own body size to navigate through cluttered environments by manipulating their flight speed (Ravi et al. \u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e2019\u003c/span\u003e). Most experiments use opaque obstacles such as dowels or walls, which would theoretically be easier to detect and avoid. But bees were even able to navigate through an experimental arena cluttered with transparent (to human eyes) obstacles without collisions and seemed to optimize their trajectories with experience (Jeschke et al. \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). This process of using motion and vision together is termed Active Vision, briefly defined as a closed loop where animals can manipulate their visual input to enhance perception and consequently the decision-making process (MaBouDi et al. \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e2025\u003c/span\u003e). In the case of spider webs, detection may be possible due to the geometry of the entire web, with the radiating lines and spirals providing a more salient target rather than when faced with just a single line, but this idea remains to be tested. Furthermore, the type of flight employed by the insect would also influence detection. The flight mode of the insect, i.e., fast/direct, gradual/curved and slow/directionless flights, has been shown to directly affect the proportion of individuals that avoided orb webs (Endo \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e1989\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eThe visual modelling approach using multispectral digital photography has many advantages; the foremost one is that it allows us to visualize an entire scene, in this case the spider web under different light conditions, from the perspective of the hoverfly. A more traditional method, such as a spectrometer to measure the reflectance spectra of the webs, would not work here because these measurements are done independent of ambient light and focus on selected points. However, there are important caveats of the efficacy of this method. Firstly, there is a lack of data on the visual acuity of most species of interest, and we often have to use the taxonomically closest option, which may not be sufficient, especially given the immense variation in insect eyes, sometimes even within the same spaces (Straw et al. \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e2006\u003c/span\u003e). Secondly, these measurements are made of a static image taken perpendicularly to the plane of the web. As noted above, insects are constantly in motion and may approach webs at any angle, which would change the view of the web (Eberhard \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e2020\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eHoverflies rely on their visual ability in several contexts, ranging from interspecific contests such as chasing behavior (Collett and Land \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e1978\u003c/span\u003e), mating behavior (Collett and Land \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1975\u003c/span\u003e), detecting the approach of flying predators such as wasps (Thyselius et al. \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e2018\u003c/span\u003e) and identifying suitable flowers to forage on (An et al. \u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e2018\u003c/span\u003e). Motion cues in particular are more relevant to detection and perception, and insects can augment their detection of obstacles or predators by the sidewise movement of the entire body (saccades, e.g., hoverflies that detect a crab spider on a flower (Yokoi and Fujisaki \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e2008\u003c/span\u003e), or through head stabilization (Collett and Land \u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e1975\u003c/span\u003e; Egelhaaf \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e2012\u003c/span\u003e). Furthermore, a recent study in \u003cem\u003eDrosophila\u003c/em\u003e showed that there are ultrafast photomechanical movements at the level of photoreceptors which significantly enhance the insect\u0026rsquo;s ability to process spatial information (Juusola et al. \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e2025\u003c/span\u003e).\u003c/p\u003e \u003cp\u003eGiven that insects can detect and avoid spider webs, the question of how spiders trap insects becomes more relevant. Spider webs have long been considered as passive sieves, but that view is changing. Spiders can deform the plane of the web such that insects do not get a complete view as they approach (Craig \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e2003\u003c/span\u003e). Furthermore, spiders are generalist predators and do not depend on any one species of insect for sustenance (Nentwig \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e1985\u003c/span\u003e). They can survive easily up to a week without prey and are accustomed to hunger (Nakamura \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e1987\u003c/span\u003e). From the spider\u0026rsquo;s perspective, all it needs is a few individuals that fail to detect the web. This can be achieved when considering that individual insects alter their flight speed and mode almost constantly. A bee flying faster on its way back to the hive should have a harder time detecting a web than one that is foraging slowly among the vegetation (Rao et al. \u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e2008\u003c/span\u003e). Further research on quantifying and comparing the flight trajectories of insects that avoid the web versus those that are caught will lead to a more complete understanding of this interaction.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgments\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe thank Derian Jaime Duran and Carlos Villa del Carmen for help in tracking the insect flights.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe project was funded by SECIHTI (formerly CONACyT), Mexico through a Ciencia Basica grant (CB-2016-01/285529) to DR and a postdoctoral fellowship to DRM.\u003c/p\u003e\n"},{"header":"References","content":"\u003col\u003e\u003cli\u003e\u003cspan\u003eAn L, Neimann A, Eberling E, Algrist H, Strube-Bloss M 3rd, Trenber S, Bennink S, Schwabe K, Alburnus C, Lunau K (2018) The yellow specialist: dronefly \u003cem\u003eEristalis tenax\u003c/em\u003e prefers different yellow colours for landing and proboscis extension. 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Naturwissenschaften 96:195\u0026ndash;200. \u003cspan class=\"ExternalRef\"\u003e\u003cspan class=\"RefSource\"\u003ehttps://doi.org/10.1007/s00114-008-0459-8\u003c/span\u003e\u003cspan address=\"10.1007/s00114-008-0459-8\" targettype=\"DOI\" class=\"RefTarget\"\u003e\u003c/span\u003e\u003c/span\u003e\u003c/span\u003e\u003c/li\u003e\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"evolutionary-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"evec","sideBox":"Learn more about [Evolutionary Ecology](https://www.springer.com/journal/10682)","snPcode":"10682","submissionUrl":"https://submission.nature.com/new-submission/10682/3","title":"Evolutionary Ecology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"insect vision, flight dynamics, predator-prey interactions, spider webs","lastPublishedDoi":"10.21203/rs.3.rs-9216396/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-9216396/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eSit and wait predators, such as orb web spiders, rely on their prey\u0026rsquo;s inability to detect them in order to make a successful catch. The spider web is a thin translucent structure that is coated with sticky glue droplets and helps in retaining flying insects once they collide with the web. Nevertheless, an approaching insect may still see and avoid the web under certain ambient conditions such as illumination. A web is more visible if the light from the sun is behind the web due to diffraction effects. Here we tested the effect of changing web appearance due to different light environments on the response of flying insects, using the orb web spider \u003cem\u003eAllocyclosa bifurca\u003c/em\u003e as the predator and the hoverfly \u003cem\u003eSphaerophoria sp.\u003c/em\u003e as the prey. We photographed the webs under different light conditions using a multispectral camera and simulated their appearance from the perspective of hoverflies. We filmed the flights of approaching hoverflies and digitised their trajectories. Our results show that hoverflies can avoid spider webs irrespective of the light environment. Hoverflies approached as close as 5 cm before deviating away from the web suggesting that their flight control allows them to avoid predators successfully.\u003c/p\u003e","manuscriptTitle":"Hoverfly response to spider webs in different light environments","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2026-04-29 13:01:29","doi":"10.21203/rs.3.rs-9216396/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"editorInvitedReview","content":"","date":"2026-04-26T14:30:28+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"107628285171158223230456465943688552101","date":"2026-04-20T16:35:07+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2026-04-20T15:11:09+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2026-03-31T10:29:16+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2026-03-31T10:28:29+00:00","index":"","fulltext":""},{"type":"submitted","content":"Evolutionary Ecology","date":"2026-03-24T22:46:33+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"evolutionary-ecology","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"evec","sideBox":"Learn more about [Evolutionary Ecology](https://www.springer.com/journal/10682)","snPcode":"10682","submissionUrl":"https://submission.nature.com/new-submission/10682/3","title":"Evolutionary Ecology","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"2f344623-7743-4757-a41c-b68e95182e75","owner":[],"postedDate":"April 29th, 2026","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"under-review","subjectAreas":[],"tags":[],"updatedAt":"2026-04-29T13:01:29+00:00","versionOfRecord":[],"versionCreatedAt":"2026-04-29 13:01:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-9216396","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-9216396","identity":"rs-9216396","version":["v1"]},"buildId":"XKTyCvWXoU3ODBz1xrDgd","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}