The Ash Twins Blog

Yip, Powers, and Aviles (2008) find that web size in a colony of eusocial spiders reflects an optimal tradeoff between having to feed a larger population and consuming larger prey through cooperative hunting. The following excerpt summarizes the findings:

Here, we demonstrate the major role that cooperation plays in solving the problem of a declining surface area to volume ratio in this social spider. Anelosimus eximius is notable among cooperative spiders—also known as nonterritorial, permanent social, or simply social—for building the largest webs and colonies among species of this social system (18). Cooperative social spiders build and maintain communal webs in which members of a colony cooperate in the capture of prey, feeding, and brood care. Colony members are totipotent and mate with each other to produce new generations of spiders that continue to occupy and expand the natal nest. Colonies grow through this process of internal recruitment until, in species such as A. eximius, a single colony’s population may on occasion reach into the tens of thousands (18). Here, we show that cooperative foraging in A. eximius allows the capture of increasingly large insects as colony size increases and that this effect is sufficient to overcome the decline in the number of insects caught per capita that results from the scaling of prey capture area per spider with increasing colony size. As a result, prey biomass intake per capita is maximized in colonies of intermediate size, thus explaining both sociality and colony size range in this social spider. This is an intriguing solution to a universal scaling problem, made possible because the “organism” in this case is a collective of units capable of cooperation.