Spiders as babysitters in social groups

Written by Thomas Hesselberg

Tuesday, 14 August 2007

Social spiders (Stegodyphus dumicola) cooperating in killing a locust. Photo: Trine Bilde.

Spiders are usually thought of as lone creatures eating everything in their vicinity up to and including members of their own species. Some spiders even show cannibalistic tendencies towards their own offspring, their mother or towards males after or even during copulation. However, not all spiders fit this stereotypic view. The social spider Stegodyphus dumicola lives in southern Africa in colonies of up to a few hundred individuals with many more female than male spiders. Male and females mate within the colony thus leading to a high degree of inbreeding and genetic relatedness. More than half of the females do not get any offspring of their own. Mor Salomon and Yael Lubin from the Ben-Gurion University in Israel found that these non-breeding females act as helpers in the colony.

They collected colonies in Namibia and transferred them into the laboratory, where they could manipulate the number of females in the colony and the number of eggs that hatched. Salomon and Lubin found that brood raised in colonies with the mother and other non-reproducing females and males were significantly larger and had greater chance of survival than broods raised in colonies with only their mother and males. This show that non-reproducing females contribute to maternal care by regurgitating food to the brood. Helping females were, furthermore, observed to sacrifice themselves at the end of their lives and allowed the young to eat them.

Source: Salomon, M. and Lubin, Y. (2007). Cooperative breeding increases reproductive success in the social spider Stegodyphus dumicola (Araneae, Eresidae). Behavioural Ecology and Sociobiology 61: 1743-1750.

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