Sociality in a bark-dwelling huntsman spider from Australia, Delena cancerides Walckenaer (Araneae: Sparassidae)

Abstract

Social behavior is reported for the first time in a member of the family Sparassidae (Araneae), the Australian huntsman spider Delena cancerides Walckenaer. Unlike any previously known social spider, this is a bark dwelling species and, thus, its sociality cannot have its basis on an aerial web, the structure that has been considered central to the evolution of sociality in other spider species. Colonies of D. cancerides may comprise up to 300 individuals living in close physical contact under the exfoliating bark of dead Acacia, Callitris and Casuarina species. Specimens maintained in the laboratory feed communally and capture prey jointly. Although this intranest tolerance and communal feeding behavior is reminiscent of other highly social spiders, D. cancerides notably differs from these other species in the extreme aggression shown towards members of foreign colonies, its outbred population structure, and lack of sex ratio bias. We suggest that sociality in this species may have been facilitated by the presence of extended maternal care in the ancestral phylogenetic lineage, as suggested by the occurrence of such behavior in related nonsocial species, and that colonial living may have arisen as a consequence of the reduction and fragmentation of Delena's habitat associated with the rise to dominance of the eucalypts. The apparent colony recognition observed may have evolved because Delena's hunting habits may require mechanisms to locate one's own colony after foraging expeditions and to exclude wandering outsiders from entering one's nest, in contrast to web-bound species that do not need to leave their nest to forage. How the observed outbreeding is accomplished in the face of Delena's extreme intolerance to members of other nests, as well as how new colonies are formed, are issues that have yet to be investigated. © 1995 Birkhäuser Verlag.