Dec 10, 2010 14:49 GMT  ·  By
The walnut sphinx caterpillar, a type of moth larva, can whistle out holes in its side, noises that can fend off attacking birds.
   The walnut sphinx caterpillar, a type of moth larva, can whistle out holes in its side, noises that can fend off attacking birds.

Who would have thought that caterpillars can whistle, but according to a new research they do, and scientists explained that the squeaks they let out protect them from attacking birds.

The whistle of a caterpillar is slightly different than a human's, since caterpillars don't have lips, but they manage to make the noise by blowing out their sides.

The researchers behind this discovery are neuroethologist Jayne Yack and Veronica Bura, at Carleton University in Ottawa.

Yack was the first to prove that silk-moth caterpillars (Antheraea polyphemus) make clicking sounds by snapping their mandibles together.

Now, along with her colleagues, proved for the first time that walnut sphinx caterpillars (Amorpha juglandis) can toot from their sides.

To make this discovery, the researchers used high-speed video and got the images of the caterpillar pulling its head back, to compress its body cavity and whistle.

Insects do not use their mouth to breathe, unlike reptiles, birds and mammals, so the only way that a caterpillar can whistle is by forcing air out the holes (spiracles) in its sides.

To verify this theory, Bura applied latex over all eight pairs of the caterpillars' abdominal spiracles and then uncovered each pair systematically while pinching the larva.

She concluded that the whistles came from the eighth pair, and could last up to four seconds, passing through frequencies audible to birds and humans, and up to ultrasounds.

The silk-moth caterpillar clicks to warn predators about being a nasty meal but what's the reason behind the whistling of the walnut sphinx caterpillar?

To answer this question, the two researchers worked with scientists from the Queen's University in Kingston, Canada, who have been studying captive yellow warblers (Dendroica petechia) – birds that eat caterpillars and live in the same environment as the walnut sphinx caterpillar.

The experiment was not so hard to set up – they put the walnut sphinx caterpillars on twigs in cages with yellow warblers and filmed what was going on.

This is how they found out that when the birds attacked, the caterpillars whistled, startling the predators and even making them fly away.

After the researchers carried out tests with three warblers and two attacks each, the caterpillars got away, safe and sound.

Yack told LiveScience that “these birds are clearly startled by the unexpected sounds coming out of this caterpillar; they dove for cover.”

The only explanation is that the birds never expect to hear these sounds from the caterpillars, so they back off.

It has been over 100 years that scientists have known that many caterpillars can generate clicking or squeaking noises.

However, it is only recently that researchers have begun to experimentally investigate the way that these noises are made and what roles are they playing.

The findings of this last research appear online in the Journal of Experimental Biology.