Families hunt more successfully: effect of group composition on hunting and communal feeding

Group activities that require an initial investment are liable to be exploited. This situation can, for example, be found in group-hunting lions, but also in subsocial and social spiders, in which several individuals capture single large prey items. Individuals could save investment by contributing less to the hunt but also during feeding by saving their external digestive enzymes. Such dynamics have been partly explored in subsocial and social web-building spiders, but are likely to differ when groups hunt in the absence of a web. Subsocial crab spiders hunt without webs and forage communally. Their nests usually comprise related individuals, although groups accept immigrating spiderlings from foreign nests, which may affect competition among group members. We aimed to test whether hunting and communal feeding differ depending on spiderling group composition and formed experimental treatments consisting of either (1) family members, (2) family members including two foreigners or (3) assorted spiderlings. Group hunting was more frequently found among family members and was positively correlated with spiderling mass increase. Family groups fed in consistently larger numbers and grew better compared with the assorted groups, but also compared with family groups including only two foreigners. The latter finding suggests that even a few immigrants may negatively affect communal activities.