"A female wasp will target a spider and immobilize it with an unknown venom injected into its mouth--at which point the wasp lays its eggs on the spider's abdomen. When the spider revives, it seems to carry on unaffected as the wasp larvae develop.
Over the course of several days, as the larvae grow riding on the spider's body, they releases a chemical that changes the behavior of its host. Instead of its normally orderly web-pattern construction, the spider begins to build a special cocoon for the larvae--controlled by the mysterious substance they emit. According to researchers:
It may be a neurotransmitter or a potential neurotoxin that alters the behavior of the spider in building the web. This is because the spider is weaving a structure of three to four spokes and a central part of the cocoon where it will be."
Newly Discovered Wasp Species Enslaves Spiders : TreeHugger
