A beetle fires a boiling spray
The bombardier beetle mixes reactants in a reaction chamber and ejects a pulsed spray of hot quinones, near the boiling point of water.
Two reservoirs hold hydrogen peroxide and hydroquinones. When the beetle is threatened they are forced into a chamber with enzymes, catalase and peroxidase. The reaction is violent, the mixture heats to about 100 °C, and pressure throws it out in rapid pulses, hundreds per second, aimed by a rotating turret at the abdomen.
Thomas Eisner and colleagues measured the temperature and the pulsing. The beetle does not melt because the chamber is lined and the discharge is brief. It is chemical defense, fully explained by chemistry. It is not an argument against gradual evolution, which was the use some popular writers tried to make of it. Intermediate glands and sprays exist all over the beetle family.
Caveats
- 'Boiling' describes the chamber temperature, about 100 °C. It is not a flame.
- The spray is a deterrent, painful and staining. It is not a weapon against large animals in the sense of a serious injury.
Sources
- 1Aneshansley D. J. et al.. Biochemistry at 100°C: explosive secretory discharge of bombardier beetles. Science 165, 1969.