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Snake uses prey's poison for defense

February 03, 2007|Alan Zarembo | Times Staff Writer

What doesn't kill the Japanese grass snake makes it stronger.

The snake eats toxic toads and uses their poison to defend itself from predatory hawks, researchers reported Monday in the Proceedings of the National Academy of Sciences.

The 3-foot-long snake, also known as the tiger keelback, stores the toxin in specialized glands on its neck.

The snake doesn't inject the poison with its bite. Instead, it arches its neck toward a predator, typically a hawk, and the poison is released if the predator bites or scratches the snake's neck.

"There seem to be extremely few examples where vertebrates take toxins from other animals," said Harry Greene, a snake expert at Cornell University, who was not involved in the study.

The toads produce the poison, a steroid, as part of their skin secretions. It has no ill effect on the snakes.

The relatively common snake is found in Japan, southeast Russia and China, Taiwan and the Korean peninsula.

Deborah Hutchinson, an ecologist at Old Dominion University in Norfolk, Va., and a team of researchers collected snakes from two locations in Japan -- one with poisonous toads and one without.

The toxin was present only in snakes that shared habitat with the toads, the researchers found.

The scientists also raised snakes in a laboratory to support their results.

Only those fed a diet of toads came to possess the poison.

The findings help explain differences in behavior among snakes.

Those living alongside toads tend to stand up to hawks, arching and thrusting their neck glands toward the predator.

Snakes that are unable to prey on toads tend to flee their predators.

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