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 – now effectively a zombie – stays alive until the adult wasps hatch.
"We don't know exactly what kills the caterpillars, but it is fascinating that the moment of death seems to be tuned to the duration of the wasp's pupal stage," says Arne Janssen of the University of Amsterdam.
and the zombie guards don't just sit there
"When they added a stinkbug, a voracious predator of wasp cocoons, the team found that 17 of the 19 parasitised caterpillars thrashed their heads around in the direction of the bug. More than half the time, this knocked the bug off the branch or made it retreat. Unparasitised caterpillars barely noticed the bug, even when it climbed on top of them."