The bombardier beetle mixes hydroquinone and hydrogen peroxide with a catalyst that causes an explosion of hot gas that can be fatal to some predators.
There are over 500 different species of bombardier beetle within the tribes Brachinini, Paussini, Ozaenini, and Metriini. Note: A tribe is a grouping above genus, but below family. View the expanded taxonomic nomenclature chart to increase understanding, HERE.
Habitat
Bombardier beetles can be found pretty much everywhere except Antarctica. You'll typically find them in grassy or wooded areas where the temperatures aren't too hot or too cold (temperate zones).
Life Cycle
Bombardiers have a life cycle similar to other beetles. They seek out a location devoid of too many predators and lay their eggs near or on a food source.
Bombardiers are carnivorous and so are the larvae that will attack whatever unfortunate soft-bodied insect is nearby. This beetle larvae uses its butt as a hatch and a trap for the unwary.
Mechanism of Defense
The most amazing part about these beetles is their mode of defense. Within their bodies, they are able to produce two chemical compounds that when mixed with a catalytic enzyme, ejects an explosive spray of hot liquid (exothermic reaction). The liquid is almost boiling between 200 and 210 degrees Fahrenheit, with Brachinus being the hottest of the tribes. Bombardiers have the ability to rotate their abdomen and shoot the volatile substance in almost any direction. See image below!
Evolution
So how did this adaptation evolve? It was a mystery for many years how this system could have become so deadly. Some have argued that this system disproves evolution as it would have blown-up inside the beetle destroying it and stopping its gene flow. Now, thanks to biochemical and genetics research, the paths that led to this are better understood. The chemicals, like all traits, would have evolved slowly from a non-lethal function, to a more deadly function. This is usually driven by predation. Foul taste would have been a good defense (and it is nasty tasting), but as predators became resistant to the bad taste, those beetles which produced a more effective chemical reaction would have survived and passed that trait on to their offspring. This is exactly what you'd expect in an evolutionary model. More evidence of this is the fact that various tribes and species have different strengths of the mixture. This is evolution at work!
Watch bombardier beetle spray a few ants. Some, don't survive.
I hope you enjoyed reading about this amazing insect.
Bonus: The Tanker bug in the movie Starship Troopers was inspired by the Bombardier beetle. Watch it in action! Not Safe for Little Kids.
Additional Video:
Deep Look (Bombardier Beetle) - https://www.youtube.com/watch?v=BWwgLS5tK80