Friday, August 9, 2013

Meet the Wasp that Turns Spiders into Zombie Construction Workers


In another post, we were talking about what happens to spiders and their webs when scientists give them a little bit of marijuana and other drugs. While researching that post, I learned that its not just humans that alter spiders’ behavior with chemicals. There’s a wasp in Costa Rica that does the same thing, in a more gruesome and sinister way, as part of its journey to adulthood. 

The tropical wasp species Hymenoepimecis argyraphaga is a parasite, and it takes advantage of an unlikely host. The web of the orb weaver spider Plesiometa argyra is normally a place where bugs meet their untimely death and become spider snacks. Using an arsenal of toxins and mind-altering chemicals, though, H. argyraphaga is able to turn the spider into a slave and a meal and its web into a safe haven.  

When the female wasp is ready to lay her egg, she seeks out a spider to help raise her child. She stings the spider to paralyze it and then lays an egg on its abdomen. Soon, the egg hatches and the larva that emerges remains attached to the spider, living on its abdomen and sucking hemolymph (kind of the arthropod version of blood) from its body for nourishment. After a few weeks like this, during which the spider goes about its life as normal, the wasp larva is ready to move on to the next stage of its life cycle. To do this, it needs to make a cocoon. A spider’s web is a decent place to build one, but not perfect. It’s suspended above the ground and the sticky threads provide defense from predators that might eat the wasp, but it’s far too flimsy to support the heavy cocoon and the adult wasp that will come out of it. 

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