The bombardier beetle is a nasty little critter. Agitate it, and you’ll be met with a caustic, near-boiling spray of chemicals fired at incredible velocity from its rear end. The chemical weapon is effective enough to allow the beetles to thrive on every continent except Antarctica with virtually no natural predators, but how does it deploy such a noxious defense without getting hurt itself? Now, new research from MIT reveals the secret.
“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,” says MIT professor of materials science and engineering Christine Ortiz.
The chemical spewed by the beetle is called benzoquinone, and is actually common among insects. What makes the bombardier beetle unique is the way it’s synthesized within the beetle’s abdomen. Using high-speed synchrotron X-ray imaging, the researchers were able to see inside the beetles at the point of expulsion. What they found was that the beetle possesses the chemical precursors to benzoquinone separately within its body, only combining them in a protected chamber before it attacks. When the two compounds mix to produce the irritant, they also create the heat and pressure needed to propel the mixture at any would-be foe.
“Their defensive mechanism is highly effective,” says MIT graduate student Eric Arndt, which makes the beetles “invulnerable to most vertebrates, and invertebrates.”
The way the beetle’s body apparently passively synthesizes the chemical is also interesting. The two chambers are bridged by a membrane that acts as a valve. When the chemical begins to build steam, the resulting pressure causes the valve to close, preventing the beetle from cooking its own insides. When the blast is released, the relaxing pressure allows the next pulse to load. This all happens rapidly within the beetle – the X-ray technology had to capture the action at 2,000 fps for scientists to see it.
The researchers say their findings may one day be applied to blast protection technology for humans. Of course, it may also prove valuable for engineers designing propulsion systems. The way the beetle’s propulsion chamber remains rigid to retain pressure and temperature, for example, stands in stark contrast to the more flexible systems that allow for the jet’s release and modulation.
Perhaps it’s no surprise, then, that the research was funded in part by the Department of Defense through the U.S. Army Research Office. In the mean time, don’t mess with bombardier beetles.