A wasp larva injects a spider with a web-altering drug, driving the spider to spin a shelter just right for a wasp cocoon.

It's "probably the most finely directed alteration of behavior ever attributed to an insect parasitoid," notes William G. Eberhard of Smithsonian Tropical Research Institute and University of Costa Rica in San Jose. In the July 20 Nature, he describes the wasps' elaborate attacks.

A female of one species of Hymenoepimecis strikes a Plesiometa argyra spider hanging in its web. She temporarily paralyzes the spider with her sting and lays an egg on its abdomen.

The spider soon perks up and spends the next week or two spinning webs as usual. Meanwhile, the egg hatches, and the larva sucks the spider's body fluid. When Eberhard removed the larva, the spider kept spinning normal webs.

Otherwise, just before the larva constructs its cocoon, it induces the spider to spin a twisted tent instead of its regular web. In the wild, the wasp then kills and eats its host and suspends its own cocoon under the shelter. However, when Eberhard removed the maturing wasp before it retires into its cocoon, the spider continued to create tents for several days, slowly regaining some of its former web style.

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