A bombardier beetle’s defense works in pulses, like a tiny living spray machine.
When threatened, the beetle mixes stored chemical ingredients in a chamber in its abdomen. Their reaction heats an irritating liquid close to boiling and pushes it outward in a directed spray. For years, scientists could observe the bursts from outside but could not see exactly how the beetle controlled them.
High-speed X-ray images of living beetles revealed a flexible membrane and valve between chambers. Pressure from one burst closes the passage; as pressure falls, it opens again for the next pulse. That arrangement lets the insect release a rapid series of hot sprays while controlling the reaction inside its body. A half-inch beetle has a surprisingly intricate way to defend itself.