How Sharing Leads to Death

Oct 14, 2016

By Veronique Greenwood

The colonial spiders of Ecuador spin homes for themselves the size of houses, wrapping cobwebs around the jungle trees where they live in groups of tens of thousands. The diminutive creatures raise young together, eat together, and die together. An apparently thriving colony can disappear almost instantly, with few or no survivors, for reasons that are still mysterious.

Biologists who study these creatures and their cousins have spun many theories about what the risk factors for collapse are, and it seems that the larger the colonies are, the greater the danger of collapse. A recent paper from researchers at University of British Columbia investigates whether a particular behavior common in large colonies—sharing prey among many colony members—might contribute to their downfall.

Ruth Sharpe, a UBC graduate student, finds her subjects by cruising along roads in Ecuador looking for clouds of bridal-veil webbing in the trees. Sharpe knew that large, spread-out colonies tend to catch larger prey than smaller ones. With a large catch, like a big wasp, it would be more difficult for a few spiders to monopolize it the way they might a small fly. A more likely scenario would be divvying it up amongst all comers. But that creates the possibility of there not being enough food to keep any of the spiders fit enough to reproduce. With small prey that can be kept amongst a few spiders, those individuals would get enough to keep the colony going, even if others eventually starve. Bad news, though, if one big wasp means only a mouthful for each member.

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