How bombardier beetles play defense with scalding spray?

In the animal kingdom, expelling a foul substance from one's rear end is a tried and true defensive mechanism. But each species makes the technique its own, and the bombardier beetle is not any different.
To thwart attackers, the ubiquitous black beetle launches a jet of scalding, irritating liquid. The technique is highly effective. But most impressive is that the beetle blasts out such a piping hot and corrosive spray without inflicting physical harm on itself. Until now, the process had scientists stumped.

New research out of MIT offers a detailed look at the the beetle's weaponry and its deployment against intruders and would-be aggressors.

The liquid spray used by bombardier beetles is called benzoquinone, but the spray isn't made until it's needed. Two chemical precursors are mixed in a protective well at the end of the abdomen. It's not until the two chemicals are mixed that benzoquinone and its irritating qualities form.

The synthesis process gives off a lot of energy, heating the benzoquinone close to its boiling point. The heat creates pressure that helps expel the liquid out the back end.

X-ray imaging allowed scientists to map this process in great detail.

"For decades, the complex mechanism of how the bombardier beetle achieves spray pulsation as a chemical defense has not been understood, because only external observations were used previously," study leader Christine Ortiz, a professor of science materials and engineering at MIT, said in a press release.

The process operates almost like an assembly line of chambers and valves -- chemicals mixed, pressure builds, chemical released in jet-like spray through valve, relax and repeat.

Researchers say the regimented and well-protected process could have implications in propulsion system design, as well as in designing blast-protection systems.

The study was published in the journal Science.