A wasp from Thailand stings cockroaches and leads it home as an insect slave. Welcome to the world of parasitoids

The Harry Potter fans among you will remember Dementors, ghostlike creatures that suck the life out of people in a creepy Dementor’s Kiss. Turns out, Dementors exist for real — but you don’t have to lose sleep over it. A bright black and red wasp from Thailand, which looks nothing like a hooded featureless Dementor, was recently given the name.

Zombie cockroaches



Female wasps of this species ( Ampulex dementor) land on cockroaches and use their sting to inject poison directly into the cockroach’s head. No amount of chocolate, not even the most effective Patronus charm, can help the cockroach. The nervous system of the cockroach loses control of the insect, though its muscles can still function. It literally becomes an empty shell, an obedient zombie, and follows the wasp back to her burrow.

The wasp’s intentions are even more sinister than having an insect slave do her bidding. She has a foolproof plan for her children: a relatively safe place for eggs, and fresh, living meat for her newborns. She lays her egg on the cockroach. The cockroach, still alive but having lost its mind, becomes a live nest. When the wasp’s eggs hatch, the larvae feed on the live cockroach till they mature.

Not for the queasy!

Watch a video of an emerald cockroach wasp which engages in a very similar behaviour here: www.thne.ws/wasp-roach

A living breathing nest



This species is not the only one to plan a live nest. A lot of wasps, called “parasitoids”, do the same. A parasitoid is an organism that spends a lot of its life attached to another organism called the host. The host does not benefit from the parasitoid at all; in fact, it usually loses its life because of the association. Parasitoids are different from parasites, where the host is affected but does not die. The mosquito that bites you is an example of a parasite.

It’s not just the common cockroach that falls prey to ghoulish female wasps. Tarantulas are huge hairy spiders that can eat up small birds and have lizards and mice for tea, but they’re no match for the female wasp. The tarantula hawk moth uses them as live incubators. Male tarantula hawks are very docile, but the female is the exact opposite. When she finds a good sized, well fed female tarantula, she stings it, paralysing it. The wasp then lays an egg inside the tarantula’s abdomen, where it will be safe and warm. When the larva hatches out, it feeds on the still-living spiders’ juices, carefully avoiding the vital organs so that its canteen — the tarantula — continues to live.

Caterpillar control



The fate of a moth caterpillar ( Thyrinteina leucocerae) goes beyond being a live incubator. Once under the sway of a parasitoid wasp that can lay as many as 80 eggs, there’s no looking back for the poor caterpillar. Two weeks after the egg laying, the wasp larvae tear through the caterpillar’s skin. Despite multiple holes on its body, the caterpillar stays alive; not just that, it watches over the wasp larvae as they spin silk cocoons within which they mature into adults. When the caterpillar senses movement nearby, it swings its head from side to side like a head banging rock star. As soon as the adult wasps emerge from the cocoons, the caterpillar dies. Its last act was to defend the very wasp larvae that killed it.

What makes this more amazing is, the wasp larvae and cocoons do not secrete any chemicals to make the caterpillar act as guardians. Two or three larvae remain in the caterpillar and control its behaviour, ultimately sacrificing themselves for their brothers and sisters.

Parasitoids and agriculture



The relationship between an insect and its parasitoid is one that has come about over thousands of years, in the process of evolution. We have been able to exploit the evolution of parasitoids and their host insects to benefit agriculture.

Many insects are pests that destroy important crops like grains and fruits. Parasitoid wasps are very specific about the insects they attack because the relationship has evolved in a specific manner.

They make for excellent controllers of insect pests.

(Sandhya is a science journalist who writes about weird and wonderful creatures. You can write to her at sandysek@gmail.com or read more on her website ‘The Melting Pot’ at www.sandhyasekar.com. )