The Beetle That Aims a Tiny Pulsed Chemistry Cannon at Whatever Bites It

A bombardier beetle is a small ground-dwelling insect that, when threatened, performs what amounts to controlled pulsed-jet chemistry on the back of its abdomen. Inside its body it stores two chemicals — hydroquinone and hydrogen peroxide — in separate reservoirs. When it's grabbed, valves let the two trickle into a thick-walled reaction chamber where catalases and peroxidases trigger an exothermic reaction. The result is a spray of 1,4-benzoquinone hot enough to redden human skin: the mixture reaches close to 100 °C, and roughly a fifth of it flashes to vapor.

That vaporization is what makes the discharge work. The pressure spike forces the spray out of the nozzle in discrete pulses — about 70 of them per discharge, at a rate near 500 pulses per second. Cornell biologist Thomas Eisner filmed this with high-speed cameras in the 1990s and showed that some African species can rotate the nozzle through 270 degrees, threading the spray between their own legs to hit a predator on any side. A typical beetle carries enough reagent for around 20 shots before reloading.

There are more than 500 known bombardier-beetle species, and they live on every continent except Antarctica. Their party trick has been cited so often by intelligent-design proponents that the chemistry was eventually reverse-engineered in detail; the consensus from the entomology side is that each step has plausible, well-documented evolutionary precursors.