Caterpillar whistles to ward off birds.

From Jen K. Item!

The walnut sphinx caterpillar has a trick up its sleeve -- er, side -- to keep birds from chomping on it. The clever bug can make an odd whistling sound, which startles birds enough that they usually just leave it alone. Researchers didn't know how it managed to make this sound, so they set up cameras and began experimenting. The results are rather strange.

Live Science reports that neuroethologist Jayne Yack at Carleton University in Ottawa has for the first time have revealed that walnut sphinx caterpillars (Amorpha juglandis) can make music from their sides.

The team used high-speed videos, latex to cover each pair of the caterpillar's eight sets of abdomina spiracles, or breathing holes, and a pair of pincers. They systematically tried out each set of holes and discovered it's the eighth set that makes the noise when the caterpillar contracts its body, forcing air through the holes to whistles when it senses a threat. The whistles can last up to four seconds each, and range in frequencies from what is audible to humans all the way up to ultrasound.

When they introduced a bird into the situation -- a yellow warbler that coexists in the same habitat as these bugs -- they found the sound definitely works to startle the birds into going away.