Bombardier Beetles explained: How their machine gun-like mechanism works

A lot of predators may have known by now to stay clear of the Bombardier beetle. The name itself connotes what kind of reception one will get when they threaten this tiny but war-ready insect.

Since it always feel threaten, its trigger happy. If any predator is unlucky enough and would try to make it food for breakfast or anytime for that matter, all they will get are those boiling hot chemicals as they shoot out in quick succession like a Gatling machine gun. And there’s nothing in the world that shoots faster than that.

According to the researchers from the University of Arizona these chemicals issue out from their abdomen and the fire power is so rapid that a ‘gun smoke’ can be seen coming out of the ‘barrel’. These chemical bullets don’t affect the beetle at all. They are immune to it.

“Understanding how these beetles produce – and survive – repetitive explosions could provide new design principles for technologies such as blast mitigation and propulsion,” said the lead authors of the study.

The research was led by doctoral student Eric Arndt and Christine Ortiz in the Department of Materials Science and Engineering at Massachusetts Institute of Technology in Cambridge.

The researchers used enzymes to clean the digestive chamber where the “ammunition” originates, and examined it with optical microscopy. They noticed some regions of the chamber wall were thicker than others, and the area near the mixing valve was particularly thin and weak.

By using enzymes, the researchers cleaned the abdominal gut of a beetle where the bullets are stacked and examined it using an optical microscopy. What they observed was that these parts are thicker than the others. The area where the mixing valves, however, were located was particularly thinner and more delicate compared to the ammo dump.

The researchers believed that the cuticula would be displaced during the firing sequence in a way that would pressure the valve and stop the flow of reactants. To find out what really happens during the salvos, the researchers took a look at the body anatomy of Brachinus elongatulus by using a hi speed X-ray machine.

“We could manipulate the beetles remotely using robots from a radiation-free control room, while the X-rays penetrated the beetle abdomen, allowing us to visualize the discharges inside,” said Wendy Moore, of the University of Arizona. “..

“For each experiment we had to cool the beetle down, carefully set it up in the observation chamber such that the X-ray beam was aimed precisely at the defensive glands, seal the doors, walk over to mission control, flip the switch to allow the X-ray beam to enter the room, and use robotic manipulators to remotely touch the beetle’s leg so it would blast. In some cases, just turning the radiation on caused them to blast.”

“The findings showed the beetles regulate ultrafast micro-pulses involved in the process in a passive way, rather than through muscle contractions. As the chemicals pass through the valve to the reactions chamber it explosively releases oxygen gas, water vapor and heat from the exit pore. Each of these explosions causes the elastic regions to expand and cut off the flow of reactants.”

“It turns out the expansion membrane of the reaction chamber acts as a passive closure mechanism, which is something that had not been described or even predicted before this study,” Moore said. “We also discovered that the chamber’s anatomy varies between female and male beetles.


The results can be read in the latest edition of the journal Science.




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