A Great Escape

How the bombardier beetle frees itself from predator toads

YOU’RE JUST A TOAD STROLLING THROUGH A JAPANESE

forest on the hunt for a snack. No one could blame you for grabbing that beetle with your sticky tongue and swallowing it whole.

Well, the beetle could blame you. And this particular species, which you have somehow neglected to kill, will make you regret your choice of food. The bombardier beetle, you see, comes equipped with chemicals that will cause you to vomit up your now mucus-coated snack. And with that, the beetle is on its merry way.

That’s the story told in a new paper, published February 7 in the journal Biology Letters. Different species of bombardier beetles exist around the globe, but researchers at Kobe University in Japan wanted to take a closer look at the bombardiers found near their campus. The subsequent report details the vomit-inducing mixture of boiling water and noxious quinones—a group of aromatic chemicals—that these beetles inject into the stomach of a hungry amphibian predator.

The study was as straightforward as science can be. The researchers gathered beetles and toads, paired some up and watched what happened. All the toads caught beetles, but following an audible burst from inside the amphibians’ stomachs, one out of every two or three beetles freed itself.

The beetles were held captive for 15 to 20 minutes. After that, the toads gagged up their stomachs and emptied them out— with a look of disgust reminiscent of a toddler tasting a first Brussel sprout. The unharmed beetles were thus liberated. Two weeks later, nearly all the regurgitated insects were still alive.

To confirm that the steamy spray was responsible for these Jonah moments, the researchers took a second batch of beetles and forced them to use up their ammunition. They poked the bugs with a pair of tweezers, triggering an instinctive release of their chemical stockpile. Later, when these defenseless beetles met their warty foes, almost none escaped.

The researchers acknowledge that their work wasn’t very fun for the toads. To reduce the damage to their subjects, the researchers were sparing with their meals. “We provided each toad with only one beetle to minimize the negative impacts,” co-author Shinji Sugiura, an entomologist at Kobe University, tells Newsweek. Sugiura adds that the toads continued to eat nontoxic prey after vomiting the bugs, indicating that no long-lasting harm was caused. The toads, by the way, were set free after their meals at the lab.