The Japanese islands snake eats toxic toads then uses the toad's poison for it's own defense in a manner that warns off predators, but is useless if challenged -- similar to a criminal waving a unloaded gun.

    Where other snakes simply tolerate toxins secreted by their prey, "this is the only snake that's truly known to use dietary toxins in its own defense," said Deborah Hutchinson of Dominion University, lead author of the study.

    The finding came when Hutchinson's colleague Akira Mori realized R. tigrinus showed some strange differences in behavior: Snakes that lived on Japanese islands with a plentiful toad population would rear up and display their toxic neck glands when a predator loomed nearby, but those on toad-free islands usually fled.

    That led Mori to suspect the snakes took the toxin from the toads they ate for supper instead of producing the toxin themselves.

    Toads secrete the toxin from their skin as a thick, white, viscous fluid that Hutchinson described as bitter and painful to predators that come into contact with it. (Because it is a cardiotoxin, in large quantity it can even stop a predator¡¯s heart.)

    To test their theory, the researchers collected both the "fight" snakes and the "flight" snakes from the islands in Japan. Analysis of the snakes' neck gland fluids showed snakes from toad-free islands lacked the toxic compounds. The team also found the glands in all the snakes lacked the cell machinery needed for a toxin factory.

    As a means of defense, the snake's toxic glands are mostly all show -- it doesn't actually release the toxin. It only displays the glands. A predator could scratch the glands on the snake's neck, thereby releasing them, but the wound would probably kill the snake.

    Toxin-borrowing is common in invertebrates (Monarch butterflies takes up milkweed toxins, for example), but less so among vertebrates, Hutchinson said, though some frogs are known to take up toxins from ants and other insects they eat.

    The researchers also experimented with snake hatchlings; when mothers were fed toad-free diets, their hatchlings were not exposed to the toxins.

    "The hatchlings lacked these compounds -- they only accumulated these toxins when [the mothers were] fed toads," Hutchinson told LiveScience.

    Mother snakes that do eat the Japanese toads can pass the toxin along to their hatchlings through the egg yolk. In this way, mothers pass on a survival advantage to their young.

    "That's a way to arm their offspring right away," Hutchinson said.

    (Agencies)