Bombardier beetles are known to expel hot liquid from their behinds as a defense mechanism, but biologists only now know how they do it. This powerful chemical attack can kill insects, drive away small animals, and even hurt humans.
Benzoquinone is superheated to the temperature of boiling water through a reaction with hydrogen peroxide. This heat assists in expelling the hot liquid, creating a pulsating jet of the noxious-smelling chemical. Much of the chemical released by the insect vaporizes on contact with the air, leaving behind a "popping" noise and a distinctive cloud of smoke.
The beetle utilizes a method of producing the jets that results in the liquid being much hotter than similar mechanisms from other insects. The stream also flies from the creature at speeds up to five times faster than usually seen in nature.
Bombardier beetles produce a chemical explosion in their abdomens which produce heat, and propels the irritating liquid toward the intended target. Biologists wanted to know how the insect - which measures just half an inch in length - could withstand such a process.
Massachusetts Institute of Technology (MIT) researchers examined the internal workings of bombardier beetles using high-speed synchrotron X-ray imaging, which recorded 2,000 frames per second of video, allowing researchers to watch the process inside the insect in extreme slow motion.
"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, material science and engineering professor at MIT, said.
A pair of chambers within the insects, separated by a valve and flexible membrane, produce the explosive reaction. One chamber holds on to the precursor chemical, while the second acts as an explosion chamber. After the introduction of the reactant to the second chamber, an explosion takes place, and the added pressure closes the valve. After release of the hot liquid, reduced pressure closes the valve, and the valve re-opens, repeating the process, resulting in a pulsating stream.
Researchers found the explosion chamber included a reinforcing structure that reduces heat absorption and minimizes stretching. Special parts of the defensive mechanism control the direction at which the jet is emitted, investigators found.
The insects exist on every continent on Earth except Antarctica, in part because no other animal eats them, due to their powerful chemical defense.
Researchers suggest this study may assist others designing blast-protection systems for humans, or could be utilized in the design of new propulsion systems for a wide range of vehicles, including rockets.
Analysis of the remarkable defensive capability of bombardier beetles was detailed in the journal Science.
Photo: David Hill | Flickr
