Carl Zimmer in his excellent blog, The Loom:
In November, National Geographic put a ladybug and a wasp on its cover. They made for a sinister pair. The wasp, a species called Dinocampus coccinellae, lays an egg inside the ladybug Coleomegilla maculata. After the egg hatches, the wasp larva develops inside the ladybug, feeding on its internal juices. When the wasp ready to develop into an adult, it crawls out of its still-living host and weaves a cocoon around itself.
As I wrote in the article that accompanied that photograph, the ladybug then does something remarkable: it becomes a bodyguard. It hunches over the wasp and defends it against predators and other species of parasitic wasps that would try to lay their eggs inside the cocoon. Only after the adult wasp emerges from its cocoon does the bodyguard ladybug move again. It either recovers, or dies from the damage of growing another creature inside of it.
How parasites turn their hosts into zombie slaves is a tough question for scientists to answer. In some cases, researchers have found evidence suggesting that the parasites release brain-controlling chemicals. But the wasp uses another strategy: there’s a parasite within this parasite.