Spiders: hunting together makes everyone full

Giant colonies secure their nutritional needs through larger prey

Anelosimus spiders work together to kill larger prey © University of British Columbia
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Eating and chasing together makes you sweat - not only for us humans but also for some spiders living in colonies. Scientists in the journal "Proceedings of the National Academy of Sciences" (PNAS) report why a tropical spider species can sustain particularly large colonies. Through cooperation, the animals catch larger prey and thus ensure the nutrition of all members of the colony.

The colony size of most social animals is limited by their ability to provide enough food for so many animals. In the case of spiders living in colonies, the surface of the three-dimensional nets used by prey animals no longer grows in proportion to the number of individuals in the colony at a certain size. As a result, the amount of prey per spider decreases and this, in turn, acts as a natural brake on colony size.

Eight meter high nets

But there is one exception: the South American spider Anelosimus eximius lives in colonies that comprise up to 20, 000 individual animals. The fishing nets of the community reach up to eight meters high in the crowns of the trees, the nest still rises after all three meters high. Somehow, this spider species must have overcome the limiting factors - but how?

That's exactly what scientists from the University of British Columbia led by zoologist Leticia Avilés have now discovered. Investigations into the Amazon region of Equador have found that spiders ensure their food supply by cooperating with each other, weaving common nets and making larger and larger prey as their colonies grow larger.

The nets of the spider colonies can grow to several meters © University of British Columbia

Bigger prey ensures food needs

"The average size of the prey made by the colony grows 20-fold as the colony size increases from less than a hundred to 10, 000 spiders, " explains Avilés. "Even if the amount of prey falls sharply relative to colony size, it increases the biomass that every single spider has as food." Researchers' observations revealed that large prey accounts for only eight percent of the total prey Spotted the colony's prey, but covered more than 75 percent of its food needs. display

"But that only works to a certain point, " says Avil s. The prey biomass reaches its peak when the colony contains 500 to 1, 000 individuals, then decreases. The new observations also provide an explanation for the spread of spiders, predominantly in tropical areas: In temperate latitudes, larger insects simply lack this type of prey-catching behavior to allow.

(University of British Columbia, 07.08.2008 - NPO)