These Beetles Use Butt-Mounted Chemical Weapons To Survive Toad Attacks

Sequential images of emetic (vomiting) behavior in a juvenile Bufo japonicus. The bombardier beetle Pheropsophus jessoensis escaped from the toad's mouth 88 min after being swallowed. Sugiura et al./Biology Letters, 2018

Aliyah Kovner 08 Feb 2018, 11:16

Many insects store bitter chemicals in their tissues to dissuade predators, but bombardier beetles see unpalatable taste and raise the self-defense game to a new level.

When threatened, special reservoirs in the beetle’s abdomen open up to mix the compounds produced within: Hydrogen peroxide in one and a mix of hydroquinones and water in another. When they meet, a potent exothermic reaction causes the resulting liquid mixture to boil before it pops violently out through a valve on the tip of the abdomen—and onto the unlucky predator trying to eat the beetle.

“You’ve got 100 degrees centigrade temperature, you’ve got a chemical burn, the steam comes off like a smoke, and then also the reaction kind of hisses,” said entomologist Terry Erwin of the Smithsonian Institute to WIRED.

All of the estimated 649 species within the bombardier family, called Carabidae and found on every continent except Antarctica, eject noxious toxins in one fashion or another, typically with impressive aim. Some even do so in rapid bursts of up to 20 excretions before running out of ammo, so to speak. Small attackers can be killed by the discharge, and larger ones are often dazed, injured, and convinced to hunt elsewhere.

The beetle’s unique adaptation has intrigued naturalists for some time, particularly after it was observed that the beetles could apply their butt rockets to escape the mouths of predatory toads. After all, the chance of survival after the jaws close is normally pretty low in the animal kingdom. 

Shinji Sugiura and Takuya Sato of Kobe University in Japan decided to test whether bombardiers could recover from the even more treacherous situation of actually being swallowed.

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