Tom Turpin
Professor of
Purdue University







Peppered Moth Isn't A Condiment

Insects are a favorite food resource for many animals, including bats. There are over 1,000 species of bats throughout the world. Food for these flying mammals includes fruit, nectar, pollen, fish and night-flying insects.

Worldwide, bats are major predators of night-flying insects. Bats in the United States feed almost exclusively upon insects and are considered beneficial animals, especially by people who don't like mosquitoes and the other insects that fly at night.

It has been shown that the mouse-eared bat can catch up to 600 mosquitoes in an hour. Other insects that become meals to bats include katydids, crickets and many moths.

Merlin Tuttle, in his book on bats, calculated that the 20 million free-tailed bats from Bracken Cave in Central Texas eat a quarter of a million pounds or more of insects in a single night. That's a lot of bugs!

Insectivorous bats are able to find their meals while flying in the nighttime by emitting a series of ultrasonic cries. These sounds are reflected by objects, and the echo is used by the bat to key in on a potential meal or to avoid flying into things. The system is a highly sophisticated sonar, so sensitive the bat can detect and catch insects even smaller than mosquitoes.

Some moths, however, also have developed a system of sonar detection. They have ears that can hear the ultrasonic sounds emitted by bats. The ears are located right behind the wings and, when the insect is in flight, it can pick up the ultrasound from all directions. In fact, the moth can detect the bat from farther away than the bat can detect it.

When a moth detects the sonar of the bat, it takes defensive action. It changes its normal flight pattern and goes into a series of loops, turns and dives. Much as would a fighter plane pilot being pursued by an enemy aircraft.

This evasive behavior by moths is sometimes demonstrated by hummingbird moths feeding at a flower bed. When disturbed, these moths drop from sight. Such was the result when an entomologist dropped his car keys and noticed that hummingbird moths, feeding nearby, disappeared. He repeated the experiment, dropping the keys again — same result with the moths! The keys clinking together apparently produced enough high-pitched sounds that the moths responded with bat-avoiding behavior.

On almost any summer evening you can witness aerial battles between insects and bats that, for sheer intensity, rival those of Snoopy and the Red Baron. An especially erratic flight pattern of a bat might mean it has detected and lost contact with a big, fat juicy moth that has just done a fancy barrel roll and dropped from the sonar screen. To the moth, such a maneuver is a matter of life or death; to the bat, it is just another tasty morsel that got away.


Writer: Tom Turpin
Editor: Andrea McCann