How These 'Exploding Beetles' Don't Blow Themselves up

When you think of beetles, you probably think of the many harmless bugs that wing around a garden looking for some tasty aphids to devour. They don't bother you, and you likely have no reason to bother them. This changes in the case of the bombardier beetle - a species infamous for its ability to spray a powerful jet of superheated chemicals that can even scald human skin.

Traditionally, the word bombardier is associated with (obviously) military personal assigned to artillery or the sighting and releasing of bombs. It then makes very little sense that insects of the Carabidae family, who spray their victims with hot fluids, would be called this.

However, past studies have revealed that for these fluids to approach the boiling point of water and expel from the beetles' abdomens in such violent streams, chemical explosions are actually occurring within the creatures. The result is a tiny percussive sound just before a victim get scalded.

The question then becomes, how the heck does an inch long beetle not blow up when detonating explosions within its own body?

"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," Christine Ortiz, a material science and engineering researcher at the Massachusetts Institute of Technology (MIT), explained in a recent statement.

That's now all changed, after the researcher and her colleagues used high-speed synchrotron X-ray imaging to peer inside the abdomens of living bombardiers. In a controlled setting at Argonne National Laboratory, the researchers poked and prodded the tiny beetles until they finally couldn't take it anymore, launching into a defensive posture and spraying an incredible pulse stream of hot fluid. The processes that prompted this reaction were recorded at a rate of 2,000 frames per second. (Scroll to read on...)

[Credit: Melanie Gonick/MIT]

So how do these little bombardiers not blow themselves up? According to the study's results, which were published in the journal Science, it's not actually one powerful explosion sending the hot fluid launching. Instead, fast and controlled pulses of explosions contained and released at just the right time were occoring within the bombardier's abdomen.

Specifically, the combination of two chemical precursors builds pressure within a specialized chamber, prompting a membrane found there to temporarily expand, this helps pressure build until the fluid pushes it's way past, collapsing the membrane and reliving that pressure. Then, just as quickly as it ended, a new explosion begins. This happens so fast that it's hard to detect an interruption in a bombardier's jet stream. However, you can definitely hear the repetitive explosions occurring within the beetle's body.

Jeffrey Dean, a professor of biology at Cleveland State University who studies the defense mechanisms of the bombardier beetle, said in a commentary that despite the fact that these findings weren't exactly unexpected, it's good to finally have the science settled.

Now researchers can even move on to using this new-found understanding of the beetle's structure as inspiration for future blast protection and combustion propulsion systems.

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