The Exploding Bombardier Beetles

Pop Goes the Beetle

Bombardier beetle illustration with cutaway abdomen.
Side view of model of black and yellow Bombardier Beetle with yellow legs, cross section showing venom glands and reservoir, explosion chamber filled with red liquid with one-way valve, side view. Getty Images/Dorling Kindersley/Geoff Brightling

If you're a small bug in a big, scary world, you need to use a little creativity to keep from being squashed or eaten. Bombardier beetles win the prize for the most unusual defensive strategy, hands down.

How Bombardier Beetles Use Chemical Defenses

When threatened, bombardier beetles spray the suspected attacker with a boiling hot mixture of caustic chemicals. The predator hears a loud pop, then finds itself bathed in a cloud of toxins reaching 212° F (100° C).

Even more impressive, the bombardier beetle can aim the poisonous eruption in the direction of the harasser.

The beetle itself is not harmed by the fiery chemical reaction. Using two special chambers inside the abdomen, the bombardier beetle mixes potent chemicals and uses an enzymatic trigger to heat and release them.

Though not strong enough to kill or seriously maim larger predators, the foul concoction does burn and stain the skin. Coupled with the sheer surprise of the counterattack, the bombardier beetle's defenses prove effective against everything from hungry spiders to curious humans.

Researchers Look Inside the Bombardier Beetle

New research, published in the journal Science in 2015, revealed how the bombardier beetle can survive while a boiling mix of chemicals is brewing inside its abdomen. The researchers used high-speed synchrotron X-ray imaging to watch what happened inside living bombardier beetles.

Using high-speed cameras that recorded the action at 2,000 frames per second, the research team was able to document exactly what happens inside a bombardier beetle's abdomen as it mixes and releases its defensive spray.

The X-ray images revealed a passageway between the two abdominal chambers, as well as two structures involved in the process, a valve and a membrane.

As pressure increases in the bombardier beetle's abdomen, the membrane expands and closes the valve. A burst of benzoquinone is released at the potential threat, relieving the pressure. The membrane relaxes, allowing the valve to open again and the next batch of chemicals to form.

Researchers suspect that this method of firing chemicals, with rapid pulses instead of a steady spray, allows just enough time for the walls of the abdominal chambers to cool between shots. This likely keeps the bombardier beetle from being burned by its own defensive chemicals.

What Are Bombardier Beetles?

Bombardier beetles belong to the family Carabidae, the ground beetles. They're surprisingly small, ranging in length from just 5 millimeters to about 13 millimeters. Bombardier beetles usually have dark elytra, but the head is often orange in contrast.

Bombardier beetle larvae parasitize the pupae of whirligig beetles, and pupate inside their hosts. You can find the nocturnal beetles living along muddy edges of lakes and rivers, often hiding in debris. About 48 species of bombardier beetles inhabit North America, mainly in the south.

Creationism and Bombardier Beetles

Creationists, who believe all organisms were made by the specific, intentional act of a divine creator, have long used the bombardier beetle as an example in their propaganda.

They assert that a creature with such a complex and potentially self-destructive chemical defense system could never have evolved through natural processes.

Creationist author Hazel Rue wrote a children's book promoting this myth called Bomby, the Bombardier Beetle. Many entomologists have skewered the book for its complete lack of scientific facts. In a 2001 issue of the Coleopterists Bulletin, Brett C. Ratcliffe of the University of Nebraska, reviewed Rue's book:

"…the Institute for Creation Research demonstrates that brainwashing is alive and well as it continues to wage its own cold war against reason in order to replace it with superstition. In this highly disjointed little book, the target is young children, which makes the authors’ sin of deliberate ignorance even more reprehensible."

 

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