from Eisner & Aneshansley 1999 (PNAS)
Bombardier beetles fart to escape predators.
Listen to find out how and why.
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Music in this show:
1. Goldfinger, “King for a day”
2. TriBeCaStan, “Bed bugs”
3. from Donald in Mathmagic Land
4. Vignatis, “Catnip swing”
5. Spanglish Fly, “Let my people bugalú” (Clay Holley and Jeff Dynamite remix)
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Transcript:
hugabug.
This here’s the first episode of hugabug, where we hug bugs instead of squishing them. Unless the bug is toxic or aggressive.
There’s this beetle that farts to escape predators. It’s called the bombardier beetle. It’s got wings, but the wings don’t work. It’s a ground beetle, so it lumbers around kind of slowly. This beetle can’t fly, and it can’t run, so when it’s threatened by death, it farts.
Wet farts would be more accurate, but explosive diarrhea actually sums up most precisely what goes on with this beetle.
Bombardier beetles have these glands on each side of their butt. I’ve heard them called “tailpipes”, but they’re glands. One gland holds nasty chemicals that smell foul and burn your eyeballs, and they’re gross. The chemicals are meant for defense against enemies; it’s like carrying mace in a creepy part of town. The other gland holds enzymes, which are like fuel for the fire–when the enzymes hit the nasty chemicals, there’s this immediate reaction that lets the beetle rip out a big, nasty, chemical fart.
You actually can hear it. People say it sounds like a pop.
What the beetle does is it squeezes the horrible chemicals into a reaction chamber of enzymes, this firing chamber, this explosion chamber. All this pressure builds up in the explosion chamber from the reaction and the release of oxygen that the whole chemical mess just spews out of the beetle’s butt and into the face of whatever’s attacking.
That’s if they’re attacking from behind; but even if the attack comes from the front, the bombardier beetle can swivel its glands and spray forward, 500 bursts of chemical reactions per second.
So imagine an ant looking for a vulnerable victim to eat. The ant finds this slow-moving beetle on the forest floor, just walking around on an old log, and the ant sinks in its mandibles.
The beetle sprays in the ant’s face, and the ant can’t even get angry and come back with rage because the spray evaporates really quickly, and a chemical cloud surrounding the beetle ensures that ants stay away, at least for a while.
Plus, there’s a chemical residue that lingers on the beetle’s butt and legs. The beetle wipes away the droplets, essentially rubbing itself with insect repellent. Which it created. In its own butt.
The toxic cocktail is bad news for other bugs and spiders and even larger animals. And if the toxic chemicals don’t hurt an attacker, the heat will get them.
Bombardier beetles shoot out scalding hot streams the temperature of boiling water. These are high-velocity scalding jets at 500 painful squirts per second. People say that it hurts.
Legend has it that Charles Darwin–Mr. Evolution himself–came across a bombardier beetle. He’s a naturalist, so he’s the kind of guy that hunts around for rocks and animals; he was looking for beetles on this particular day. I guess he didn’t bring containers, or maybe he couldn’t reach them in his pockets, because he had two valuable beetle species–one in each hand. He spotted another bug that must have been too beautiful to let go, and he had to act quick to get it, so he stuck one of the beetles in his mouth and reached for the third. The following is paraphrased from one of Darwin’s letters to a friend[1]: “…so that in despair I gently seized one of the [beetles] between my teeth, when to my unspeakable disgust & pain the little inconsiderate beast squirted his acid down my throat & I lost [all 3 bugs].” So you may not want to try and catch these guys with your bare hands, and especially not with your mouth.
All of this is true. We have been talking about the real world here, but in our own lives, these bombardier beetles actually show up, somehow, in ways you maybe wouldn’t expect.
The mechanism of the bombardier beetle’s wet fart is actually similar to a weapon from World War II. The German “buzz” bomb (the V-1, it’s called) uses pulse jet propulsion that’s similar to the beetle’s rapid butt-spray. Both the beetle and the bomb produce a pulsed jet through these “microexplosions”, which are intermittent chemical reactions.
Plus, some researchers built an experimental contraption that mimics the spray action of the bombardier beetle. Such technology can make your shaving cream warm as you spray it out of the can and is designed to “administer a lather that is pleasantly hot”[2].
And that is the story of the beetle that farts to defend itself.
I don’t know whether a beetle like this can get bamboozled by its enemy into being eaten. Maybe if it’s caught by such surprise, or maybe if it’s old and frail, or already dead or something. Nor do I know how this beetle survives the scalding hot toxic mess that must splash onto itself in these desperate situations. But it’s something to think about.
This is a snack–not a meal–of science, but it is all you will get on hugabug this week. You just remember–hug a bug.
from Dean et al. 1990 (Science)
(Click the picture to see it larger)
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Other related things around the internet:
Video of a bombardier beetle spraying an ant. Action starts at 0:50; includes a great fart noise at 1:58.
What the heck, NPR? An artist’s rendering of the bombardier beetle and its attacker, a beetle’s-eye view.
Tom Eisner, entomologist extraordinaire, invited Mira Sorvino to teach one of his classes at Cornell University. Eisner named a beetle chemical after her.
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just a couple References:
l i z w a s o n 
Great piece! You squeezed a lot that expounds on the science into 5 minutes: Darwin (science history), WWII (world history) and technological applications (every capitalist’s dream of what science is good for – in the past, present, and future).