Centipedes: a life story.

The state of the universe.
July 18 2011 10:23 AM

Cranky Little Bastards

Taking stock of the centipede.

More revolting creatures: the eel, the skunk, the snapping turtle, the vulture, the tick, the jellyfish, the hyena, the slug, and the mosquito.

Centipede. Click image to expand.
The centipede

The man who walked a cable between the two towers of the World Trade Center said he was calm and unafraid 1,638 feet above the ground, without a net.

What is Philippe Petit afraid of?

"Things with too many legs, and not enough legs." (As he told NPR's Peter Sagel.)

M. Petit was probably thinking first of spiders and snakes, but it's centipedes that go to extremes in the leg department. Eight works for spiders, two seems fine to us, so centipedes, with between 20 and 300 legs, seem to be overreaching. But their limb version came first. They're the Earth's oldest terrestrial animals, zipping around on all-hundreds for the past 450 million years.

Centipedes went the multilegged route for speed in catching prey. The showy statistic is for the house centipede—Scutigera coleoptrata—timed running at 42 centimeters per second. With a body size of just 2 centimeters, this little creature is the cheetah of arthropods. Unlike their relatively benign myriapod cousins, the millipedes, they're meat-eaters.

When they start galloping after some tasty morsel, how do they decide which leg to move first? Did some Ordovician proto-centipede obsess over the matter, and trip over its very many ankles? Like good tap dancers, the ones that survived seem to have gotten the message: Don't overthink it.

A centipede's body hangs from the legs, giving it stability. That speedy house centipede, the little one we're likely to see in the bathtub, shows this form most obviously with its 15 pairs of outrigger legs resembling false eyelashes. All centipedes' multisegmented bodies are extremely flexible, adapted for pursuing things like silverfish and termites in crevices. They're the top predator in their environment of leaf litter, earth, rotting logs, and, in the case of the house centipede, damp basements and drains.

With limbs to spare, centipedes could modify their first pair of legs into fangs. (Most poisonous creatures form their fangs from mouthparts.) These inject a paralyzing venom that contains, among its 30-some components, a kind of meat tenderizer that speeds the paralyzing effect and softens up the prey. As Greg Edgecombe, resident centipede maven at the Natural History Museum in London, put it so vividly, "They homogenize the contents and slurp it out like soup."

Slide Show: Revolting Creatures. Click image to launch.

Centipedes eat various insects, plus worms, spiders, and, sorry, other centipedes. But New Yorkers take note: They also eat cockroaches and bedbugs. Though the fangs of the house centipede, and most of the other small ones, can't pierce human skin, it would take a very tough city dweller to welcome a centipede into bed. (Related cultural note: Rebbie Jackson, elder sister of Michael, made a music video of the song "Centipede," co-starring a tiger, a cobra, and a chorus of young men in black tie. Informed sources say the title refers not to the myriapod but to an orgy involving 100 people. A less cheery, truly gross pop culture phenomenon—the movies Human Centipede and Human Centipede 2—demonstrates that evolution is a lot better than a mad scientist when it comes to creating viable, many-legged creatures.)

Tropical centipedes, up to a foot long, consume bigger quarry than bedbugs. They'll bite and tenderize and slurp amphibians, reptiles, birds, and rodents. Southern Arizona has an 11-inch lizard-eating centipede with a sting like a scorpion's. There's new evidence of the big guys' nimbleness and ambition. Even veteran centipede researchers like Edgecombe were astonished by a recent video of centipedes hanging from the roof of a cave and catching bats. The bite of one can cause swelling, chills, fever, and tissue death in adult humans. They don't kill very many of us, but even a smallish centipede can be dangerous to children and those allergic to bee stings. As with the venomous cone snail and poisonous reptiles, pharmaceutical companies are looking at how centipede neurotoxins could work as useful anesthetic in small doses.

Animals with large numbers of a body part, like centipedes, turn out to be very useful to those who study the evolution of developmental processes—a field now given the bouncy name Evo/Devo. The Evo/Devo-ers are trying to understand how complex organisms develop from a single fertilized egg, and the production of repeating pairs of legs offers some important clues. Since various orders, families, and species of centipedes have different numbers of legs, scientists can compare their patterns of gene expression to better understand how animal bodies are segmented and differentiated. An understanding of the relevant genes—called homeoboxescould tell us a lot about the cause of human malformations.

That's why some of the thousands of scientists who've been studying the development of fruit flies have lately shifted to centipedes. They're not the ideal lab animals, however. They may be easy to find—Arctic to tropics, rain forest to desert, just turn over a rock—but if you put two in a bottle at night, there will be one in the morning. And they reproduce very slowly, compared with flies. Lab fruit flies can go from egg to reproducing in two weeks; centipedes take at least a year to go from egg to adult and then live for up to another half-decade after that. (Geneticists prefer a quick turnover.)

Besides being prone to cannibalism, how do centipedes behave? "It would be unfair to call them cranky little bastards," said Edgecombe, of the Natural History Museum, strongly implying that they are cranky little bastards. They're not heavy on brain matter, and it looks as though there's not much leisure or pleasure in their lives. Since they don't copulate, there's no opportunity for ecstatic sexual release, though centipedes do know how to slow-dance. The male reaches out his antennae and taps the last segment of a female. He performs some gyrations to signal that he's making a sperm packet. There's a special organ for spinning the packet, which Edgecombe referred to as "a sad ass little willy."

Few have closely observed centipede reproduction. No one knows how the male persuades his intended that his sperm packet is superior to anyone else's, or if he even tries. The female picks up the packet, in most species moving it with a special pair of legs into her genital opening.

Those who study centipedes rush to say that the creatures are good mothers. They may sit for as long as three months without eating, watching their eggs and then seeing the young through their first few molts. The desert centipede coils around the eggs and grooms them, to prevent fungus from growing.

Exterminators exploit our fears about the many-legged beasts, but in fact the smaller and more common centipedes do more good than harm. If your home is clean and dry and, most important, free of the things that are centipede chow, you shouldn't be bothered by them. Though the small ones can't bite through our skin, it's best to tell children not to pick them up. What to do if you find one? If it's a foot long, run. If it's an inch or two long, sweep it into a jar and chuck it out in the garden. If it's very little, pick it up with tissue paper, look at it, and think back on our last common ancestor—a marine worm that lived about 560 million years ago. We've taken a different path since then, of course, but we're all creatures made of segments.

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