The jewel wasp (Ampulex compressa) is a bright, iridescent creature; one with a particular way of making sure its larvae get food. A mixture of hunting, poison and mind control make up its impressive repertoire. It starts when a female wasp finds a cockroach.
Upon finding the cockroach the wasp descends and stings it twice. The first sting strikes the midsection of the cockroach, this sting immobilises the cockroach’s front legs. The second strike goes directly into the brain of the cockroach, the wasp pumps in a specialised venom that doesn’t kill, but instead changes how the cockroach acts entirely.
The new cockroach is not paralysed, but confused. It will not flee from danger. In its new state the wasp moves to the front of the cockroach and grabs an antenna. Then it leads the cockroach on a walk like a dog on a leash. Dumbly the cockroach continues on, the venom working its brain precisely, until they reach the wasp’s nest.
The wasp lays an egg on the cockroach’s belly then seals the cockroach inside its nest before leaving. Over the next day or so the cockroach remains stupefied, even when the eggs hatch and a larva emerges. Then the power of the brain venom is shown. The larva begins to burrow into the cockroach, eating its flesh, live; the cockroach does nothing to stop it, and so it dies. A fantastic, if gruesome event, but how did it work?
The question of what the venom did exactly had been bugging scientists for some time, until light was shed on it by Ram Gal and Frederic Libersat of the Ben-Gurion Institute. They did the science and found that, in short, it made the cockroaches very lazy. The science started with a zap of electricity.
Mild electric shock does the same things to cockroaches as it does to humans, namely causing twitching, mild annoyance and allowing balloons to stick to them. A small chamber was set up where about half of the floor could be electrified, when the shock put through it was enough to make a cockroach leg twitch, cockroaches normally scuttle to safety. Not so with the stung cockroaches.
4 hours after being stung, the cockroaches needed 10 times the normal shock to get them to move, even though their legs seemed to be just as responsive. Not only that but they needed about 4 of the strong shocks to make them move reliably. They felt the same shocks, but weren’t responding.
They could move just fine, when provoked they could fly perfectly normally, and when put on their backs they wiggled just as vigorously to get back onto their legs. Their motor control was fine, the only difference was in their brain, in the venom.
The venom is very precise, tailored so specifically to the cockroach brain that it only affects the specific neural circuits associated with walking. It made them not want to walk, enforcing such extreme laziness that they let themselves be eaten alive. A true feat of evolution and precision engineering. The venom only lasts for three days but that is no help to a cockroach, by then in the wild, they would be as dead as dinner.
Not Exactly Rocket Science Article