Autotomy in Spiders: An Overlooked Natural History Adaptation with Ecological Costs

Autotomy, or voluntary limb loss, is a widespread defense strategy among arthropods, yet its ecological costs and benefits in spiders remain poorly documented. Here, we report natural history observations of leg autotomy in 32 species across eight families from four coastal wetlands in Kerala, India. Patterns of autotomy varied widely, with many species, including members of the orb-weaving Araneidae, and others shedding legs at the coxa–trochanter joint to minimize hemolymph loss, while agile hunters such as members of the family Salticidae and Oxyopidae frequently autotomized multiple legs with potentially severe locomotor consequences. Notably, repeated cases in the jumping spider Carrhotus viduus highlight the trade-offs faced by active hunters that depend heavily on agility. These findings underscore the adaptive value of autotomy as an escape strategy while emphasizing its hidden ecological costs. We argue that autotomy warrants greater attention within ecological and evolutionary frameworks, as it illustrates how survival strategies are balanced against long-term performance in natural communities.

Autotomy, or voluntary limb loss, is a widespread defense strategy among arthropods, yet its ecological costs and benefits in spiders remain poorly documented. Here, we report natural history observations of leg autotomy in 32 species across eight families from four coastal wetlands in Kerala, India. Patterns of autotomy varied widely, with many species, including members of the orb-weaving Araneidae, and others shedding legs at the coxa–trochanter joint to minimize hemolymph loss, while agile hunters such as members of the family Salticidae and Oxyopidae frequently autotomized multiple legs with potentially severe locomotor consequences. Notably, repeated cases in the jumping spider Carrhotus viduus highlight the trade-offs faced by active hunters that depend heavily on agility. These findings underscore the adaptive value of autotomy as an escape strategy while emphasizing its hidden ecological costs. We argue that autotomy warrants greater attention within ecological and evolutionary frameworks, as it illustrates how survival strategies are balanced against long-term performance in natural communities. Keywords: Autotomy, anti-predator strategies, spider ecology, behavioral adaptation, survival trade-offs

Escape from predation is one of the strongest selective forces shaping animal adaptations, often driving the evolution of specialized defensive behaviors (Edmunds,1974, Cooper and Blumstein 2015). Among these, autotomy - the voluntary shedding of a body appendage, is a dramatic yet widespread survival tactic observed in a variety of animal groups. The strategy represents a trade-off: while it provides immediate benefits by 1 Posted on 27 Aug 2025 — The copyright holder is the author/funder. All rights reserved. No reuse without permission. — https://doi.org/10.22541/au.175628391.13893649/v1 — This is a preprint and has not been peer-reviewed. Data may be preliminary. facilitating escape from predators, it imposes potential long-term costs on locomotion, reproduction, and overall fitness (Maginnis 2006). While autotomy has been well-studied in many invertebrate groups such as crabs (Juanes and Smith 1995) marine invertebrates (Jobson et al. 2024), scorpions (Mao and Zhang 2024), and insects (Emberts et al. 2017, Starr and Sarmiento 2021, Jubb 2024; O’Neil et al. 2024)), spiders have received comparatively less attention in autotomy research, even though they represent a hyperdiverse lineage with remarkable ecological and behavioral diversity. Previous studies have noted that spiders can shed legs at predetermined breakage planes, typically at the coxa–trochanter joint, minimizing hemolymph loss (Foelix 2011, Tahir et al. 2015). Yet, most existing literature focuses on laboratory experiments, and field-based natural history observations remain scarce. Here, we report observations of leg autotomy in 32 spider species from coastal wetlands of Kerala, India. We document its taxonomic distribution, variation in patterns across families, and potential ecological costs. These findings suggest that spider autotomy deserves renewed attention as a survival strategy, contributing to broader discussions on the balance between immediate survival and long-term ecological performance.

Field surveys were carried out between 2019 and 2022 in four coastal wetlands of central Kerala, India: Changaram (9°47’50’ ’N, 76deg17’20’ ’E), Kadamakkudy (10.06519degN, 76.2451386degE), Kandakkadavu (9deg51’29”N, 76deg16’1”E), and Puthuvype (9.977degN, 76.226degE. These wetlands are characterized by a mosaic of mangroves, open water bodies, and riparian vegetation, supporting diverse arthropod communi- ties. Spiders were collected opportunistically and through hand-sampling during field surveys. Instances of autotomy were noted during capture, handling, or post-capture observations. Each specimen was identified to species or morphospecies level using standard identification keys (Sebastian and Peter, 2009; World Spider Catalog, 2025). For each individual, the following details were recorded: species and family, sex, leg(s) shed and laterality, and point of detachment. Photographic documentation was made for representative specimens.

A total of 32 spider species representing eight families were observed to exhibit autotomy (Table 1 and Figs. 1-32). Family Oxyopidae (lynx spiders) had the highest representation, with nine species recorded, followed by jumping spider family Salticidae (seven species), Clubionidae (five species), Sparassidae (three species), and smaller numbers from other families. Patterns of autotomy varied among families. Many species, including orb-weaving araneids such as Argiope catenulata andCyrtophora moluccensis , as well as representatives of other families, exhibited leg detachment at the coxa–trochanter joint, a mechanism that minimizes hemolymph loss and reduces the risk of fatal injury. In family Clubionidae, both males and females displayed autotomy, with some individuals shedding multiple legs, reflecting behavioral flexibility in their defensive responses. Spiders of the lynx spider family Oxyopidae displayed the most diverse cases, with as many as nine species shedding variable legs (e.g., R2, L3, L4), indicating reliance on rapid escape and agility. Within Salticidae, repeated cases were recorded in Carrhotus viduus , suggesting significant costs for species dependent on precise locomotion. In Sparassidae, large species such as Heteropoda venatoria autotomized as a last-resort survival strategy, while in Thomisidae, females of Thomisus projectus shed legs after failed ambush attempts.

Autotomy was observed across a taxonomically diverse assemblage of spiders, reflecting its evolutionary importance as an anti-predator defense. While autotomy enhances immediate survival, limb loss imposes 2 Posted on 27 Aug 2025 — The copyright holder is the author/funder. All rights reserved. No reuse without permission. — https://doi.org/10.22541/au.175628391.13893649/v1 — This is a preprint and has not been peer-reviewed. Data may be preliminary. functional trade-offs, particularly in hunters such as salticids and oxyopids. The repeated observations of autotomy in Carrhotus viduus indicate high ecological costs for active hunters that rely on precision and agility. These observations illustrate how autotomy is differentially expressed across lifestyles. Sit-and-wait predators such as araneids and thomisids may tolerate limb loss without severe impairment, while active hunters such as salticids and oxyopids incur significant performance costs. Such family-level differences reflect the interaction between microhabitat, predation pressure, and locomotor strategy. From an evolutionary perspective, autotomy exemplifies a trade-off between immediate survival and long-term fitness. Surviving predation is paramount, but impaired locomotion may reduce prey capture, reproductive success, or increase vulnerability to future threats. Our observations highlight autotomy as an overlooked yet ecologically sig- nificant adaptation in spiders. The phenomenon raises several unresolved questions: (a) How frequently do autotomized individuals regenerate lost limbs, and at what cost? (b) What are the population-level consequences of frequent autotomy? (c) Do predators adjust their hunting strategies knowing spiders can autotomize? We suggest that spider autotomy deserves systematic study alongside other survival strategies such as web modification, cryptic coloration, and venom use. By integrating natural history observations with experimental approaches, autotomy can serve as a model for understanding how organisms balance instantaneous survival with long-term ecological performance.

Cooper, Jr., W.E. and Blumstein, D.T. 2015. Escaping from predators: an integrative view of es- cape decisions. Cambridge University Press. https://doi.org/10.1017/CBO9781107447189 Edmunds, M. 1974. Defence in animals: A survey of anti-predator defences. Longman. Emberts, Z., Miller, C.W., Kiehl, D. and St. Mary, C.M. 2017. Cut your losses: self-amputation of injured limbs increases sur- vival, Behav.Ecol. 28 (4): 1047–1054. https://doi.org/10.1093/beheco/arx063 Foelix, R.F. 2011. Biol- ogy of Spiders. 3 rd Edition, Oxford University Press, Oxford. Jobson, S., Hamel, J. and Mercier, A. 2024. Shake it off: exploring drivers and outcomes of autotomy in marine invertebrates. Biol. Lett. 2020240015. https://doi.org/10.1098/rsbl.2024.0015 Juanes, F. and Smith, L.D. 1995. The ecological consequences of limb damage and loss in decapod crustaceans: a review and prospectus. J. Exp. Mar. Biol. Ecol . 93: 197–223. http://hdl.handle.net/10088/18451 Jubb, L. 2024. Staggering stink bugs: autotomy affects stability and locomotor performance in Halymorpha halys . Longwood Senior Theses. 41. https://digitalcommons.longwood.edu/senior theses/41 Maginnis, T.L. 2006. The costs of autotomy and regeneration in animals: a review and framework for future research. Behav. Ecol. 17: 857–872. https://doi.org/10.1093/beheco/arl010 Mao, A. and Zhang, S. 2024. Autotomy does not affect the locomo- tor performance of a scorpion. Integr. Zool. 19(2):336-338. https://doi.org/10.1111/1749-4877.12767 O’Neil, J.N., Yung, K.L., Difini, G., Rohilla, P. and Bhamla, S. 2024. Limb loss and specialized leg dynamics in tiny water-walking insects. Integr. Comp. Biol. 64 (3): 1034–1043. https://doi.org/10.1093/icb/icae077 Sebastian, P.A. and Peter, K.V. 2009. Spiders of India. Universities Press, Hyderabad. Starr, C.K. and Sarmiento, C.E. 2021. Sting Autotomy. In: Starr, C.K. (ed) Encyclopedia of Social Insects. Springer, Cham. https://doi.org/10.1007/978-3-030-28102-1 Tahir, H.M, Naseem, S., Zahra, K., Akhatar, U., Mumtaz, R., Khalid, R. and Nouman, M. 2015. Autotomy: an important tool in spiders to avoid life threatening situa- tions. Biologia (Pakistan). 61 (2): 329-333. World Spider Catalog. 2025. World Spider Catalog. Version 26. Natural History Museum Bern, online at http://wsc.nmbe.ch, accessed on 22 August 2025. doi: 10.24436/2 Hosted file oik-11961-File003.docx available at https://authorea.com/users/960243/articles/1329043- autotomy-in-spiders-an-overlooked-natural-history-adaptation-with-ecological-costs Hosted file oik-11961-File004.docx available at https://authorea.com/users/960243/articles/1329043- autotomy-in-spiders-an-overlooked-natural-history-adaptation-with-ecological-costs 3