The following is an excerpt, used with permission, from an article by Carl Zimmer that appears in the November 2014 issue of National Geographic.
A predator protected from other predators, the ladybug would seem to have the perfect insect life—were it not for wasps that lay their eggs inside its living body.
One of these wasps, Dinocampus coccinellae, is about the size of an ice-cream sprinkle. When a female wasp is ready to lay an egg, she alights near a ladybug and swiftly injects an egg into her victim along with a blend of chemicals. When the egg hatches, the larva feeds on the fluids that fill its host’s body cavity.
Though the ladybug is gradually being devoured, on the outside it seems unchanged. It goes on attacking aphids with abandon. But after it has digested its prey, its parasite feeds and grows on the resulting nutrients. Some three weeks later, the wasp larva has grown so much that it is ready to leave its host and develop into an adult. It squirms out through a chink in the ladybug’s exoskeleton.
Even though the ladybug’s body now is free of the parasite, its mind remains enthralled. As the wasp larva wraps itself in a silk cocoon beneath it, the ladybug remains immobile.
From the wasp’s point of view, this is a very positive development. A growing D. coccinellae wasp nestled in its cocoon is intensely vulnerable. Lacewing larvae and other insects will happily devour it. But if one of these predators approaches, the ladybug will thrash its limbs, scaring off the attacker. In effect it has become the parasite’s bodyguard. And it will continue to loyally play this role for a week, until an adult wasp cuts a hole through the cocoon with its mandibles, crawls out, and flies away.
Only then do most of the ladybug zombies die, their service to their parasite overlord complete.