Brain-punking Parasites, Pt. 2

February 13th, 2007

Continuing in my series on zombification, we turn our eye from Soviet Cold War efforts and suicide-inducing Gordian worms to the Ampulex compressa, a parasitoid wasp that strikes fear into the heart of cockroaches everywhere.

Similar to the Gordian Worm, 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.

Attempts by scientists to mimic the Emerald Wasp’s surgical skills have been met with limited success - the test subjects dehydrate and die well before those attacked in the wild. Quite how A. compressa manages to override the cockroach’s nervous system and metabolism is still an area of ongoing research, and a fascinating one at that.

Read Carl Zimmers’s superior retelling of this gruesome tale over at ScienceBlogs.

Entry Filed under: Awesome Science Videos

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