A Secret Weapon
by Kim Schuelke
A black water bug lies motionless under a rock. The bug is dead, but something moves inside him. When the first spring rains drizzle down, a shiny, black bombardier beetle crawls out of the bug’s belly.
The bombardier started out as an egg. First he lived in a mud ball on a twig. He crawled onto the water bug and ate it until it died. Then he crawled inside of it and kept eating. Now he is a bombardier beetle, a little smaller than the tip of a pencil eraser.
A beetle’s head is the first of his three body parts. His head has two antennae, which help him smell. Next comes his middle, or abdomen. Two pair of wings and three pair of legs are attached to his middle. His bottom, called a thorax, is the third part. The bombardier’s flat, oval thorax hides his secret weapon.
How can the bombardier hide his shiny, black body from the sharp eyes of a bird? He can’t fly, so he spends a lot of time hiding. When the sun goes down, he sneaks out. He darts around on his six legs, sniffing out small insects. When he finds one, he grabs it with his razor sharp mandibles. Mandibles are the jaws of a special kind of chewing mouth. They look like tiny curved chopsticks. The bombardier’s mandibles point straight out, to help him eat other insects.
Suddenly, the bombardier beetle senses a bird approaching. The bird swoops in. The bombardier stands on his back legs. He mixes chemicals in his thorax. The bird is ready to bite. The bombardier bends his thorax under his body. He shoots.
Pop! Out comes a nasty smelling acid. It blinds and burnds the bird’s skin. Poof! Out comes a puff of blue smoke. The bird becomes confused and frightened. Off it goes to find an easier meal. The secret weapon has worked again.
Scientists have studied the bombardier beetle for over one hundred years. They found out that the bombardier can shoot twenty times in a row before he needs to rest. He never misses his target. They also found out that even a the tiniest drop of bombardier’s acid burns!
To you or me, most bombardiers look alike. Entomologists-the scientists who study insects-know better. Bob Davidson manages the insect collection at Carnegie Museum of Natural History in Pittsburgh, PA. Like other entomologists, he tells the different kinds apart by studying the beetles’ reproductive parts. “The parts work like lock and key sets,” he explains. The male’s part is the key and the female’s is the lock. The two parts have to match exactly to work together.” Tiny differences in the parts identify several thousand different subspecies.
Almost anywhere you live, there may be bombardier beetles nearby. Put on some old clothes, grab a magnifying glass, and head for the nearest lake or stream. Search for a dead bug and watch it for awhile. You might get to see a baby bombardier crawl out. Then, be glad you’re not a bird looking for dinner!
Aneshansley, D.J. and Eisner, T. “Biochemistry at 100 degrees centigrade: Explosive Secretory Discharge of Bombardier Beetles (Brachinus)”, Science, 165, 4 July, 1969.
Berror, Donald J. and White, Richard E. National Audubon Society: A Field Guide to the Insects of American North of Mexico, Botston: Houghton-Mifflin, 1970.
Craighead, F.C., Insect Enemies of Eastern Forests, Washington: U.S.Dept. of Agriculture Bureau of Entomology and Pland Quarantine, (Miscellaneous Publications, #657): 1949
Davidson, Robert, Carnegie Museum of Natural History, Pittsburgh, PA. Interview, 13 May 2001.
Klots, Alexander and Elsie, Insects of North America, New York: Doubleday and Company. 1969.