These butterflies boost their hearing with an unusual strategy

Think of it as a biological antenna. Researchers have discovered a species of butterfly that enlarges its wing veins to pick up sounds it wouldn’t otherwise hear—a strategy that may be critical to its survival.

Many butterflies possess tiny ears, often in the form of membrane-covered cavities at the base of their forewings. But scientists didn’t know the insects could boost their hearing with other parts of their bodies.

To make the new discovery, researchers collected 30 common wood nymphs (Cercyonis pegala)—which have unusually swollen forewing veins—and played them low-frequency sounds (relative to the spectrum of insect hearing), like a high-C note on a piano. The team then examined how the insects’ ear membranes vibrated in response, first with the veins intact and then again after making small incisions in them.

When the forewing vein was damaged, the wood nymphs’ ears were less sensitive overall, particularly to low frequencies between 750 and 5000 hertz, the team reports today in Biology Letters . The audio boost may help wood nymphs pick up a broader range of frequencies in their forest environment, which could be critical for detecting potential predators.

Although the scientists aren’t yet sure how the vein helps tune the wood nymphs’ ears, they suspect the extra air contained in the vessel could pump up the pocket beneath the ear’s membrane and allow it to distinguish between smaller changes in pitch.