Insect Ears

Humans detect the direction a sound comes from by comparing the difference in time of arrival or loudness of the sound reaching our two ears.

We can do this is because our ears are separated by the width of our head. A sound wave traveling from the left reaches the left ear sooner, and is louder than at the right ear. But if our ears were right next to each other we would lose this stereoscopic hearing.

Ormia ochracea (a tiny parasitic fly) females deposit their larvae inside a live cricket. The larvae develop inside the cricket before they emerge, eventually killing the host.

The females locate crickets by ear, using only the sound of cricket chirps to guide them. But with ears separated by less than half of a millimeter, the time and intensity difference between a fly’s ears should be much too small to detect. So how do Ormia do it?

It turns out that the Ormia ear is quite unusual. The fly’s two ear drums are connected in the middle by a small jointed bridge. The connection between the two ears is a form of mechanical coupling. It acts as an amplifier of the minute differences between the two ears. This unique anatomy allows Ormia flies to accurately detect the direction of cricket chirps!