The secret to the Jewel Wasp's 'captivating' abilities lies in a neurotransmitter called octopamine in the cockroach's brain that contols its movements.

The wasp's venom blocks the octopamine, literally converting the cockroach into a zombie.

This 'zombie' cockroach is completely unable to fight back as it is pulled by the wasp into its underground lair. If you're wondering why the wasp would go through all this trouble to just eat a cockroach, here's the really weird part -- the cockroach is meant to unwillingly play the part of surrogate mother. The wasp lays an egg into the cockroach's abdomen, and the larva later hatches and eats the live cockroach from inside out. It takes 3 or 4 days for the larva to hatch, after which it slowly feeds on the roach's internal organs, keeping it alive the whole time. This process takes about 7-8 days, during which the meat needs to be fresh for the larva. And because a dead cockroach rots within a day, the wasp prefers the 'stun' method. Once the roach is eaten up completely and it dies, the larva forms a cocoon inside it. A fully-grown wasp emerges from the cockroach carcass a month later.

The Jewel wasp is quite clean and precise in its injection of the venom. It starts by stinging the cockroach around its midsection. By doing this, the front legs are paralyzed. Then, the wasp proceeds to make a more precise sting, injecting the venom directly into the brain to block the octopamine. At this point, the cockroach is still able to move around and can flee if it wants to. But that's the trouble, the venom works on the roach's free will causing it to lose all motivation to run away from potential danger and pain. So now the wasp is pretty much free to coerce the cockroach into the direction of its choice by tugging and guiding its prey. And you know what happens next.

Jewel wasps are normally found in the tropical regions of Africa, India and the Pacific islands. In a single mating session, a female wasp is able to produce enough fertilized eggs to place on several dozens of cockroaches. The phenomenon is so fascinating that scientists have conducted several experiments in an attempt to understand it better. Over the course of several investigations, they've figured out that octopamine is quite similar to noradrenaline in humans, which is involved in the fight-or-flight reaction in the vertebrate brain. They found out that the wasp injects the venom into a very specific area of the roach's brain. So when researchers reversed the process by injecting an octopamine-like substance into the same part of a 'zombie' roach's brain, it resulted in significant recovery and restoration of its free will. Scientists have also observed that the Jewel wasp will sting a cockroach continuously for up to 3 minutes in order to determine the right spot, the sub-esophageal ganglia.

The Jewel wasp is one-of-a-kind, the only known parasite that injects its venom directly into its host's brain. But there are other parasites that control their prey's behavior in several ways. Makes you wonder at how amazing-yet-scary nature is, doesn't it?

For decades, scientists have tried to understand the complex and gruesome relationship between the parasitic emerald wasp Ampulex compressa and its much larger victim, the common household cockroach Periplaneta americana.

At first glance, this parasite-prey relationship seems much like any other: the female wasp stings the cockroach, lays an egg on its abdomen, and once hatched, the hungry larva feeds on the cockroach. However, while most parasitic insects tend to paralyse their victims with a venomous sting, the emerald wasp instead manipulates the cockroach’s behaviour, essentially transforming it into a zombie slave.

With two stings the cockroach is left with the ability to walk, but is entirely robbed of the power to initiate its own movement. The wasp, now tired after administering two stings, regains its energy by cutting off the ends of the cockroach’s antennae, and drinking its blood. Revitalised, it then latches on to the stung cockroach’s antennae and, much like an obedient toddler being lead to his first day of school, the submissive insect follows the wasp’s orders.

In the meantime the wasp also lays an egg on the cockroach, which hatches after three or four days. The hatched larva chews its way into the cockroach’s abdomen, where it proceeds to eat the internal organs in a precise order. This ensures that the docile victim stays alive for the next four days, until the larva eventually forms a cocoon inside it.

With time, the fully-grown wasp emerges from the host’s body and continues this vicious cycle. Through it all, the stupefied roach, although able to move, shows no desire to struggle, flee, or fight, even as it is being eaten alive from the inside.

How to control a roach

This wasp-cockroach relationship has been documented as early as the 1940s, but it wasn’t until recently that scientists have been able to understand how exactly the wasp pulls off this precise behavioural manipulation.

The first sting, administered to a mass of nerve tissue in the cockroach’s thorax, contains large quantities of gamma amino butyric acid (GABA), and complementary chemicals called taurine and beta alanine. GABA is a neurotransmitter that blocks the transmission of motor signals between nerves, and, together with the other two chemicals, it temporarily paralyses the cockroach’s front legs. This prevents the cockroach from escaping while the wasp inflicts the second, more toxic sting directly into the roach’s brain.

It is the second sting that turns the cockroach into a zombie, and contains what Frederic Libersat and his colleagues at Ben Gurion University refer to as a “neurotoxic cocktail”. The venom of the second sting blocks the receptors for another neurotransmitter called octopamine, which is involved in the initiation of spontaneous and complex movements such as walking.

Libersat has shown that unstung cockroaches injected with an octopamine-like compound show an increase in walking behaviour. Those injected with a chemical that blocks octopamine, however, show a reduction in spontaneous walking, much like the victims of the wasp sting. Zombie cockroaches were also able to recover from their stupor and walk after they were injected with a chemical that reactivates octopamine receptors.

There is a fine distinction between the ability to walk, and the ability to initiate such a movement. The stung cockroaches in this instance are devoid of the latter, while their skills for the former seem intact, demonstrated by the fact that these poor creatures are entirely capable of walking to the wasp’s nest, but only when being led by the wasp.

Libersat and colleagues investigated this interesting phenomenon by placing stung cockroaches in potentially harmful situations and testing their escape reflexes. They found that cockroaches stung by the emerald wasps were soon deprived of any will to escape to safety even when electrocuted or drowned. However, their motor skills, measured by the contractions of their muscles when subjected to these dangers, were the same as unstung cockroaches, suggesting that the venom affects the decision rather than the ability to walk.

However haunting this behavioural manipulation is, one can’t help but appreciate the ingenuity of this tiny parasite, enabling it to incapacitate a much bigger victim. If the wasp were to paralyse the cockroach, it probably would not be able to carry it back to its lair. If it were to kill the cockroach, it would lose its source of fresh food. It has evolved to develop the most complex and precise weapon to overcome these two obstacles: venom that only targets the specific neural circuits which guarantee that its victim will walk obediently to its tomb, and stay alive while it is being devoured. And with no will to escape, these poor roaches help another generation of terrifying emerald wasps to be spawned.

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 defense 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.