Ampulex compressa - The emerald cockroach wasp (the jewel wasp of Sabah)

The emerald cockroach wasp or jewel wasp (Ampulex compressa) is a parasitoid solitary wasp of the family Ampulicidae. It is known for its unusual reproductive behavior, which involves disabling a live cockroach and using it as a host for its larva.

Ampulex compressa thus belongs to the entomophagous parasite

This wasp stings a cockroach in the brain to take away its escape reflex and then steers it with its antennae into its burrow and lays its larva on it. With it's escape reflex disabled, the cockroach will just rest there while the wasp larva burrows into it's body, eats it internal organs and then pupates inside its body.

As early as the 1940s it was published that wasps of this species sting a roach twice, which modifies the behavior of the prey. A recent study using radioactive labeling proved that the wasp stings precisely into specific ganglia. Ampulex compressa delivers an initial sting to a thoracic ganglion of a cockroach to mildly paralyze the front legs of the insect. This facilitates the second sting at a carefully chosen spot in the cockroach's head ganglia (brain), in the section that controls the escape reflex. As a result of this sting, the cockroach will now fail to produce normal escape responses.

The wasp, which is too small to carry the cockroach, then drives the victim to the wasp's den, by pulling one of the cockroach's antennae in a manner similar to a leash. Once they reach the den, the wasp lays an egg on the cockroach's abdomen and proceeds to fill in the den's entrance with pebbles, more to keep other predators out than to keep the cockroach in.

The stung cockroach, its escape reflex disabled, will simply rest in the den as the wasp's egg hatches. A hatched larva chews its way into the abdomen of the cockroach and proceeds to live as an endoparasitoid. Over a period of eight days, the wasp larva consumes the cockroach's internal organs in an order which guarantees that the cockroach will stay alive, at least until the larva enters the pupal stage and forms a cocoon inside the cockroach's body. After about four weeks, the fully-grown wasp will emerge from the cockroach's body to begin its adult life.

The wasp then saws off the tips of the roach's antennae and drinks the hemolymph from them. It builds a nest - just a little funnel made of soil and pebbles and leads the roach, by pulling at its anteanna as if it was a dog-leash, into the funnel. It then lays an egg onto the leg of the roach, closes off the antrance to the funnel with a rock and leaves. The roach remains alive, but completely still in the nest for quite some time (around five weeks). The venom, apart from eliminating all defence behaviors of the roach, also slows the metabolism of the cockroach, allowing it to live longer without food and water. After a while, the wasp egg hatches, eats its way into the body of the roach, eats the internal organs of the roach, then pupates and hatches. What comes out of the (now dead) cockroach is not a larva (as usually happens with insect parasitoids) but an adult wasp, ready to mate and deposit eggs on new cockroaches.

the Emerald Cockroach Wasp is free-living as an adult, but chooses to give its young a head-start in life by parasitising a living cockroach. After mating, the female wasp seeks out a suitable host and paralyses it with a quick sting to the thorax. This, however, is only the beginning of a slow and (we must imagine) painful death as the cockroach is systematically zombified, digested, and killed.

The first sting serves only to buy A. compressa enough time to deliver a second, more precise sting, directly into the cockroach’s brain. Guided by sensors on the side of her sting, the wasp probes into the brain of the cockroach. Upon finding a particular spot, the wasp delivers a second venom, disabling the cockroach’s escape reflex.

As the paralysing venom wears off, the cockroach does not run away. Instead, passive and obedient, it allows the wasp to seize it by the antenna and lead it back to the wasp’s burrow, to meet its fate.

Once there, the wasp lays an egg on the underbelly of the zombie roach, and seals the sonambulant victim in by blocking the entrance with pebbles. In time, the egg hatches and a tiny larva chews a hole in the side of the roach, worming its way into the host. Once there, the larva begins to digest the still-living cockroach, eating it from the inside. Once sated, the larva spins a cocoon inside the roach and develops into an adult. As a grim finale, the adult wasp bursts out of the cockroach and the life cycle of A. compressa begins once more.