Spiders are generally solitary, aggressive, and even cannibalistic, but a few species have learned to get along. Among a species of comb-footed spider (Anelosimus studiosus), for example, some females live in multi-female colonies, sharing duties like web upkeep and raising offspring. These social moms are more docile than other spiders—they are less responsive to prey in their webs and more fearful in simulated predator attacks—but this mellow attitude comes with a cost. In a study published this month in Ecological Entomology, biologists picked out brooding females from solitary and social nests, transferred them into new webs, and forced them to go it alone. More than twice the number of juveniles of antisocial mothers made it to adulthood than those of gentle spiders, possibly because the more belligerent mothers are better at providing food. That may explain why friendly spiders are so rare: Of nearly 40,000 spider species, fewer than 50 are social.
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