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Do Not Fuck With This Beetle

New research finally explains the corrosive explosions of the bombardier beetle.
Image: Charles Hedgcock

There are more than 500 distinct species of bombardier beetle worldwide—40 in the United States alone—and they can be found on every continent in nearly every sort of climate, save for Antarctica. The prevalence shouldn't be surprising, however, as this expansive class of arthropod has developed one of the most unfuckwithable defense mechanisms in nature: boiling hot sprays of corrosive chemicals. As a result, the beetles have basically no natural predators, crawling the Earth with something like impunity—the human beings of the bug world.

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Last week, researchers from MIT, Brookhaven National Laboratory, and the University of Arizona published a study in Science explaining one of the lingering mysteries of the bombardiers—namely, their ability to produce these brutal chemical explosions without harming themselves in the process. Consisting of a bleach-like chemical called benzoquinone, the substance itself isn't such a rarity in the insect world, but the ability to generate such temperatures almost instantly is highly strange.

"Bombardier beetles are unique in using an internal explosive chemical reaction to simultaneously synthesize, heat, and propel their sprays," the study authors, led by MIT materials scientist Eric Arndt, explain. "The mechanism of brachinines' [bombardier beetles'] spray pulsation has not been understood because previous studies, relying on external observations, have not probed internal dynamics."

Arndt and his team sought to rectify this with electron microscopy, a technique that allowed them to actually see inside of the beetle and watch the process unfold at 2,000 frames per second. To do so, they utilized a specialized facility at Argonne National Laboratory capable of producing X-rays via a synchrotron particle accelerator at a very high rate.

The beetles are able to achieve their explosive defense by using pulses rather than a continuous spray. The bombardiers have a series of chambers and valves in their beetle butts, beginning with a reservoir of reactant chemicals (hydrogen peroxide, mostly) and ending in the explosion chamber. In between is a passageway that expands and contracts to allow droplets of reactant to mix with peroxidase and other enzymes (in the explosion chamber) that catalyze a chemical reaction producing both benzoquinone and extreme heat, which is released in an explosion that has the additional effect of closing the reactant valve (via pressure). This opening and closing is thought to allow for a short cooling off period between bursts, a protection mechanism.

After the explosion, the reaction chamber relaxes, allowing another droplet of reactant in and the process starts over. This happens at an average rate of 667 Hz, or 667 times per second, which is bafflingly fast. It's all very clever, and will probably only provide more ammo to creationists, who are fond of using the bombardier as an example of intelligent design: "Common sense tells us that the bombardier beetle's cannon which can fire four or five "bombs" in succession could not have evolved piece by piece," goes a post at answersingenesis.org, for example. (Motherboard: reading creationist barf so you don't have to.)

The point of the research isn't in disproving creationists, however. It might even have some very real-world applications, as Arndt and his team note: "An understanding of how brachinine pygidial glands produce (and survive) repetitive explosions could provide new design principles for technologies such as blast mitigation and propulsion."