Bombardier beetles can be found on most continents around the world, but this species is found only in North America. Bombardier beetles of all types generally live in temperate zone woodlands or grasslands. It feeds mostly on smaller insects and hunts them during the day under logs, big rocks, or other dark, damp places.
Any place will do for a ground beetle to lay its eggs, so long as it's out of the way of most predators, but not too far away from a good food source. Small underground tunnels or cracks in rotting wood are viable places, as are the decomposing remains of other living things. When the egg hatches it goes into the larval stage where it begins alternately taking in nourishment from the food source and molting. After it molts for the last time it metamorphoses into a pupa. At the end of the pupal stage, the pupa sheds its skin and a new adult bombardier beetle emerges. Ground beetles tend to live for several weeks.
Bombardier beetles are incredible creatures, truly deserving the attention they have received. They earned their common name from their ability to defend themselves against predators by firing a mixture of boiling-hot toxic chemicals from special glands in their abdomen. These beetles have two small glands located near the end of its abdomen. One gland produces hydrogen peroxide and the other hydroquinone. When disturbed, the beetle releases these two chemicals into what is called the "explosion chamber" where the enzymes catalase and peroxidase are added. These enzymes speed up the reaction to a level where the beetle can make an audible "pop" as it ejects the now-boiling chemical stream toward whatever unlucky predator happened to disturb it. Added to this, the beetle can rotate the end of its abdomen 270 degrees in any direction, which allows for an impressive "firing range." In effect, the beetle can spray in whatever direction the predator comes from.
In this defense mechanism, secretory cells produce hydroquinones and hydrogen peroxide which collect in a reservoir. The reservoir opens through a muscle-controlled valve onto a thick-walled reaction chamber. This chamber is lined with cells that secrete catalases and peroxidases. When the contents of the reservoir are forced into the reaction chamber, the catalases and peroxidases rapidly break down the hydrogen peroxide and catalyze the oxidation of the hydroquinones into p-quinones. These reactions release free oxygen and generate enough heat to bring the mixture to the boiling point and vaporize about a fifth of it. Under pressure of the released gases, the valve is forced closed, and the chemicals are expelled explosively through openings at the tip of the abdomen.
The reason that the beetle has the name "false" comes from creative literature accounts that give a false description of the explosive reaction that the bombardier beetle produces. A poor translation of a 1961 article by Schildknecht and Holoubek claimed that hydrogen peroxide and hydroquinones would explode spontaneously if mixed without a chemical inhibitor, and that the beetle starts with a mix of all three and adds an anti-inhibitor when it creates the explosion. In fact, the two do not explode when mixed, as others have demonstrated. Schildknecht did propose a physical inhibitor which kept the mixture from degrading in undisected beetles. The degradation he saw was probably simply a result of exposure to the air. Gish still used the mistaken scenario after being corrected by Kofahl in 1978. The same mistake is also repeated in books by Hitching in 1981, Huse in 1983 and 1993, and twice in a creationist magazine in 1990.
Rick DuBose
Nate Bellamy
Insect Biology & Diversity - Fall 2002
