At first glance, colonies of thousands of social spiders all look the same and are busy with the same tasks. Not so, say researchers Carl Keiser and Devin Jones of the University of Pittsburgh, after carefully studying various gatherings of Stegodyphus dumicola social spiders of the Kalahari Desert in South Africa.
They found that a particular spider’s body size and condition indicate which task it generally performs within a colony. Spiders with smaller bodies were more likely to help with web building and maintenance. Those who were in better condition tended not to capture prey, while those with lower body condition were more likely to be busy with foraging.
“The results are intriguing because this trait variation and its resulting task differentiation gives rise to a cooperative breeding society composed of highly related, inbred individuals,” said Keiser. “The spiders are of nearly identical age and develop together in synchrony. Our findings differ from the once conventional reasoning among social spider researchers that social spider societies are homogenous and egalitarian.”
In addition, they found that neighboring colonies can have different “personalities.” A colony’s “personality” — or collective behavior — is best predicted by the variety of individual spiders living within it. Colonies with members with different body sizes or aggression levels contained spiders which were slower to emerge from their nest to attack prey. Variation in boldness within colonies is in turn linked with better chances that more individual spiders will take part in standard web building activities.
Stegodyphus dumicola spiders live in colonies of up to 2,000 members in thorn trees in the arid parts of southwestern Africa. The spiders build large webs consisting of dense communal living areas and a two-dimensional capture web. To study them, Keiser and his colleagues transported various colonies collected in the southern Kalahari Desert to their laboratory at the University of Pittsburgh. They then carefully watched to what extent individuals were involved in tasks such as attacks, web building, or web repairing.
Keiser and his colleagues believe that such studies are vital to understand how the traits and actions of individuals combine to form and develop the social organization and collective behavior of a particular species.
Their study is published in the journal Behavioral Ecology and Sociobiology.
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