Spiders: Social Evolution

Spiders are predatory and cannibalistic, and most of them are not social. Nevertheless, group living has arisen independently in several spider families. Group-living spiders are divided into colonial and cooperative-breeding species. Colonial spiders share a living space, but forage individually, compete for prey, and do not cooperate in raising young. Cooperative (social) spiders construct communal webs, and feed and raise young communally. Colonial species have originated from precursors that aggregated around resources, while social species have likely evolved from subsocial forms with extended maternal care. Colonial and social spiders can subdue large prey and are protected from predators through increased vigilance. Colonial species have juvenile dispersal and are assumed to outbreed. Juvenile dispersal is lost in the social species and they inbreed regularly. Cooperation and female-biased sex ratios enable colonies of social species to grow rapidly and proliferate.