According to the New Scientist article, the parasitoid wasp Glyptapanteles lays its eggs, about 80 at a time, in young geometrid caterpillars. The eggs hatch and the larvae feed on the caterpillar's body fluids. When they are fully developed, they eat through the caterpillar's skin, attach themselves to a nearby branch or leaf and wrap themselves up in a cocoon.
At this point, something remarkable and slightly eerie happens: the caterpillar, still alive, behaves as though controlled by the cocooned larvae. Instead of going about its usual daily business, it stands arched over the cocoons without moving away or feeding. The caterpillar stays alive until the adult wasps hatch.
15 June 2008
The Poor Mouth: Zombie caterpillars controlled by voodoo wasps: