Bombardier beetles: nature's 'buzz bombs.'

Bombardier beetles: Nature's 'buzz bombs'

When escape seems unlikely, harassed "bombardier" beetles resort to a remarkable natural example of chemical warfare, a defense known to science for many decades. "These beetles on being siezed . . . immediately . . . play off their artillery . . . burning . . . the flesh to such a degree that only a few specimens can be captured with the naked hand," naturalist John O. Westwood wrote in 1839.

Now chemical ecologist Thomas Eisner of Cornell University and his colleagues have discovered that some species of bombardier beetles deliver their defensive spray in trains of millisecond-length pulses, rather than in continuous streams. What's more, "the ejection system of the beetle shows basic similarity to the pulse jet propulsion mechanism of the German V-1 'buzz' bomb of World War II," they report in the June 8 SCIENCE.

When another creature yanks on one of its legs or antennae, a bombardier beetle contracts muscles in glands that store chemical reactants in separate compartments. This forces the previously segregated reactants through a one-way value in each gland into an underlying reaction chamber, where enzymes convert the chemicals into the spray's active ingredient (benzoquinones), while liberating lots of heat. The accompanying surge in pressure spits the hot chemicals from the chamber through a "gun-turret" in the beetle's abdomen.

"You see a little puff of smoke" and hear a little popping sound, Eisner told SCIENCE NEWS. The seemingly singular puffs and pops actually are composed of short pulses, each lasting about two-thousandths of a second. Acoustic recordings and readings from force sensors placed in the path of the spray yielded the first evidence for the pulses. Using high speed cinematography technology developed by the late Harold Edgerton of MIT, the researchers also filmed the individual pulses.

The scientists postulate that the initial pressure on the gland side of a valve drives reactants into the chamber. As the chamber pressure quickly builds during the ensuing reaction, the passive valve closes and the chamber's contents explosively eject through the opening. The now lowered chamber pressure once again allows reactants from the gland to push through the valve. Each spray consists of two to 12 such pulses.

The German V-1 "buzz" bomb worked according to a strikingly similar principle. "Both the beetle and the V-1 engender a pulsed jet through an intermittent chemical reaction, and both have passively oscillating valves controlling access to their reaction chambers," the scientists write.