What nocturnal beetle defends itself by spraying a boiling hot chemical mixture?

The nocturnal beetle that sprays a boiling-hot chemical mixture for defense is the bombardier beetle.

Bombardier beetles are ground beetles in the family Carabidae, with more than 500 species in the Brachininae and Paussinae subfamilies. Many hunt at night, but their most famous feature is their defensive spray rather than their nocturnal lifestyle.

When threatened, the beetle mixes hydrogen peroxide and hydroquinones in a reaction chamber at the tip of its abdomen. Enzymes trigger a rapid exothermic reaction that produces heat, pressure, and irritating quinones. The resulting spray approaches the boiling point of water and is expelled with a popping sound.

The beetle can aim the discharge toward predators, sometimes in several directions. The spray is not literally fire, and “boiling” describes its temperature and violent chemical release. Stag beetles, scarab beetles, and fireflies have different defenses and do not possess the bombardier beetle’s characteristic pulse-jet-like system.