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Previous entry: what I saw ...

Monday, 27 February 2006
Perspiration

drops

I had another go at the droplets on the roof of my car the other morning, and this photo is the result. The light is not as interesting, but the drops give better coverage.

Having thoroughly enjoyed the last Karl Pilkington podcast, I am looking forward to the next instalment. I see that his pimp, Ricky Gervais, wants to charge for it this time so I will probably miss it. Or else I just won’t pay. Whatever.  One of Karl’s stories (or was it Ricky’s) concerned the parasite/host relationship. Well, via Boring Boring (what the hell I’m in an insult one, insult all mood tonight), comes a link to The Wisdom of Parasites on Corante, with the gruesomly glorious story of the wasp named Ampulex compressa.

As an adult, Ampulex compressa seems like your normal wasp, buzzing about and mating. But things get weird when it’s time for a female to lay an egg. She finds a cockroach to make her egg’s host, and proceeds to deliver two precise stings. The first she delivers to the roach’s mid-section, causing its front legs buckle. The brief paralysis caused by the first sting gives the wasp the luxury of time to deliver a more precise sting to the head.

The wasp slips her stinger through the roach’s exoskeleton and directly into its brain. She apparently uses sensors along the sides of the stinger to guide it through the brain, a bit like a surgeon snaking his way to an appendix with a laparoscope. She continues to probe the roach’s brain until she reaches one particular spot that appears to control the escape reflex. She injects a second venom that influences these neurons in such a way that the escape reflex disappears.

From the outside, the effect is surreal. The wasp does not paralyze the cockroach. In fact, the roach is able to lift up its front legs again and walk. But now it cannot move of its own accord. The wasp takes hold of one of the roach’s antennae and leads it—in the words of Israeli scientists who study Ampulex—like a dog on a leash.

The zombie roach crawls where its master leads, which turns out to be the wasp’s burrow. The roach creeps obediently into the burrow and sits there quietly, while the wasp plugs up the burrow with pebbles. Now the wasp turns to the roach once more and lays an egg on its underside. The roach does not resist. The egg hatches, and the larva chews a hole in the side of the roach. In it goes.

The larva grows inside the roach, devouring the organs of its host, for about eight days. It is then ready to weave itself a cocoon—which it makes within the roach as well. After four more weeks, the wasp grows to an adult. It breaks out of its cocoon, and out of the roach as well. Seeing a full-grown wasp crawl out of a roach suddenly makes those Alien movies look pretty derivative.

Carl Zimmer of Corante also advises that the wasp is not technically a parasite but a exoparasitoid. I have a phobia of cockroaches and spiders, but this story appeals to me. Perhaps because the roach gets it.

Posted by bigblue on 27/02/2006 at 11:22 PM
Filed under: EuropeUnited KingdomEngland • (0) CommentsPermalinkBookmark or Share

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