Foraging behavior across paths that vary in risk cues and frequency of occurrence

Cooperatively foraging species often adjust their search strategies in complex environments to efficiently find and exploit food sources. These strategies become more complicated when food and risk can be simultaneously present and when they differ in predictability. For example, there may be multiple paths to reach a foraging site that vary in risk. This study examines how colonies of Argentine ants ( Linepithema humile ) respond to such a situation where identical-length paths differ in how they present risk. The risk cues are either a live competitor (velvety tree ants, Liometopum occidentale (LO)) or formic acid (FA), a defensive chemical commonly associated with formicine ant species. Across four paths to food, the presence of cues also varied from always to never present. Although the non-risky path was used more often, in no case did colonies completely avoid the paths with risk. Overall, more L. humile workers explored paths associated with LO than with FA. This had a significant impact on foraging ability where LO colonies were faster at finding food than FA colonies. Further, L. humile workers’ response to FA was similar over time while declined for LO, suggesting a ‘dear enemy’ habituation and reduction in aggression over time. Thus, it appears that L. humile foragers categorize risk cues and will vary their responses in potentially effective ways.