What beetle defends itself by spraying a hot, noxious chemical mixture?

The beetle that defends itself by spraying a hot, noxious chemical mixture is the bombardier beetle. When threatened, it combines hydroquinone and hydrogen peroxide inside specialized abdominal glands. Enzymes trigger a rapid chemical reaction that produces heat, pressure, and irritating quinones, which the beetle expels through an outlet at the tip of its abdomen.

The spray can approach the boiling point of water and is released in rapid pulses, often with a popping sound. A valve system helps protect the beetle's internal tissues while directing the discharge toward an attacker. The main irritant, benzoquinone, can harm the eyes and respiratory system of predators.

“Bombardier beetle” is a common name for more than 500 species, especially members of the ground-beetle subfamilies Brachininae and Paussinae. They are found on every continent except Antarctica. Despite the dramatic defense, they are ordinary predators for much of their lives, commonly hunting other small insects at night.