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Fastest Snake Mouth in the West

24 November 1999 6:00 pm
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Wolfing Down. Texas threadsnakes gulp larvae by raking their jaw like no other snake.

Vipers and cobras may conjure images of lightning-fast strikes, but once snakes have grabbed their prey they need a good long while to swallow and digest it. Now scientists have documented an exception to such leisurely dining. The Texas threadsnake eats unlike any other, cramming food into its mouth at a frenetic pace. There's no need to lock up your pooch, though; the tiny snakes, described in tomorrow's Nature, are barely thicker than a piece of spaghetti.

Armed with six rows of teeth, almost all snakes also have extremely mobile upper jaws. Once a frog or an antelope is caught, a snake will grip with one side of its jaw, while the other ratchets forward. This essentially walks the head over the prey, with the lower jaw serving as a platter.

But those table manners are well documented. Nate Kley, an evolutionary biologist at the University of Massachusetts, Amherst, was more intrigued by a rarely seen burrowing snake from northern Mexico and the southwestern United States. A bantam creature, tipping the scales at under 1.5 grams, Leptotyphlops dulcis and its kin eat mainly social insects and their larvae. It sneaks into anthills and gorges on these often ferocious insects.

What's really weird--at least for herpetologists--is the lower jaw. The looseness of its three joints, located at the chin and on either side, means that threadsnakes have an extremely mobile lower jaw. To figure out how the snakes exploit this jaw-dropping flexibility, Kley rigged up a Plexiglas trough with a high-speed video camera underneath. "What first struck us as being crazy is the speed at which they're eating," says Kley, who worked with his adviser Elizabeth Brainerd. The threadsnakes were raking their lower jaw in and out of their mouth up to four times a second. And rather than independently ratchet the sides of the jaw backward and forward like most snakes, Kley's videos revealed that both sides of the lower jaw moved in synchrony.

The new work provides details on biomechanics that could shed light on the evolution of such bizarre feeding, notes biologist David Cundall of Lehigh University in Bethlehem, Pennsylvania. "We may be able to ask more refined questions about the relationships of Leptotyphlops to other supposedly primitive snakes."

Whatever its evolutionary origin, the jaw structure makes perfect sense for these underground raiders. "For burrowing snakes, you can't spread your jaws wide apart in a narrow tunnel," notes evolutionary morphologist Kenneth Kardong of Washington State University in Pullman. "This group of little snakes seems to have solved the problem by raking with their jaws. It allows them to swallow prey and get out of there."

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