Cooperation and conflicts during prey capture in colonies of the colonial spider Parawixia bistriata (Araneae: Araneidae)

Abstract

Intraspecific aggregations and colonial structures in orb-weaver spiders can reduce the per capita amount of silk to be spun, allow the use of habitats which are unavailable for solitary species, and increase protection and foraging efficiency. However, conflicts between colony members can occur during web construction, repair, and prey capture, contributing to group dissociation under conditions of low prey availability and/or in specific stages of spider maturation. While small juveniles are benefited by the joint action of many spiders during prey immobilization, older and large individuals are able to capture all available prey by themselves. For those large individuals, interactions with neighbours may compromise the amount of available resources. In this context, we evaluated the frequency of foraging events involving cooperative hunting and conflicts between residents and intruders in very young and older juveniles of Parawixia bistriata, a colonial orb-weaver spider. We recorded foraging behaviour in natural conditions and identified the main groups of insects intercepted at the webs and captured by the spiders. We then used two prey types (Lepidoptera and Orthoptera), with distinct behaviours when intercepted, in an experiment to test the influence of prey type and mass on cooperative and aggressive interactions. Most captures occurred without the participation of other individuals, and the main prey types were small Diptera and Coleoptera. Cooperative behaviour seems to occur especially between young spiderlings, but depending on prey type and size, it also occurs in late instars. The frequency of conflicts was similar in both periods of observation (November and December), with young and older individuals in colonies. Our results indicate that prey type is an important factor determining the frequency of interactions during foraging events in colonies of P. bistriata and that large spiders usually obtain success in conflicts. We suggest that these conflicts over large items may constitute a relevant variable involved in colony dissociation before spiders’ maturation.