Moths mimic "don't eat me' sounds.

Some moths defend themselves from hungry bats by mimicking the sounds of other, bad-tasting moths, according to new tests. This trick represents the first confirmed acoustic example of classic defensive mimicry.

The study's unpalatable moths, members of the tiger moth family, pick up noxious chemicals from plants that they feed on as caterpillars. A bat unwise enough to catch one of these moths typically spits it out fast.

When a bat swoops near, tiger moths make bursts of "click-click-click" sounds. A young bat hearing clicks and then snagging a vile mouthful learns to avoid the moths, according to earlier work by William E. Conner at Wake Forest University in Winston-Salem, N.C.

To see whether other moths could protect themselves by mimicking those clicks, Jesse Barber, also at Wake Forest, raised bats from babyhood in large, netted enclosures where he could control when they first encountered various prey.

At some point, he included clicking, unpalatable tiger moths among the nightly flying snacks. After 5 nights, all the bats had learned to avoid that species. Then Barber substituted a different tiger moth species. A few bats sampled the newcomers before avoiding them, but the majority avoided them from the outset.

In another experiment, Barber offered milkweed tussock moths to 10 bats. These moths click, but they're palatable. Three bats discovered that the new moths were edible, but the other seven didn't catch on.

That means clicking works both as Mullerian mimicry (two unpalatable species benefiting by making similar sounds that predators can learn by catching either one) and Batesian mimicry (edible prey borrowing an "unpalatable" signal), says Barber. The work appears in the May 29 Proceedings of the National Academy of Sciences.