You could call the bombardier beetle the dinner date from hell.
When threatened, the beetle shoots a hot jet of boiling chemicals from its rear end, and that’s not all. If eaten by a frog or toad, the bombardier beetle can launch its chemical attack from inside the stomach to force its predator to vomit it back up.
Almost half the time, the beetle survives its brief sojourn through the amphibian digestive tract, Japanese researchers report Tuesday in the journal Biology Letters.
It’s the first time the beetle has been spotted using its rear assault to survive being swallowed. Other animals have escaped after being swallowed by predators, including one live blindsnake that emerged, alive and well, after passing through a toad’s entire digestive system. However, this is one of the first instances of an entire species using this strategy.
Shock and Awe
Bombardier beetles aren’t especially rare; more than 500 species live on every continent except Antarctica, and all of them create a toxic brew of chemicals in a special chamber at the bottom of their abdomen.
The molecules are mixed together at the last minute and react to form hydrogen peroxide and another class of compounds called benzoquinones, along with huge amounts of heat and pressure. Both chemicals are irritants and can damage skin and lungs.
Thanks to the shape of the chamber, this boiling foul mixture is ejected with a huge force.
“It makes this squeaky pop,” says Wendy Moore, an entomologist at the University of Arizona who was not involved in the study. “It’s shocking. It really gets your attention, and it’s definitely effective against collectors.”
While studying these chemical defenses, researchers and Takuya Sato of Kobe University in Japan fed a beetle to the Japanese common toad Bufo japonicus. Forty-four minutes after its meal, the toad vomited up its meal. Strikingly, the beetle was none the worse for wear.
Sugiura says that the beetles were known to force predators to spit them out before being swallowed, but he had never before seen a frog or toad vomit one up after eating it.
Intrigued, he and Sato decided to test the beetles’ ability to force toads to regurgitate. They compared two species of toad, B. japonicus and B. torrenticola, and fed them Pheropsophus jessoensis, a bombardier beetle found throughout Japan and Korea. In half the beetles, the researchers depleted the insects’ supply of toxic chemicals by gently prodding them with a stick, causing them to release their spray.
All of the beetles deprived of their chemical weapons were eaten and fully digested. But of the beetles that could spray, 43 percent were vomited up between 12 and 107 minutes after being consumed.
Larger beetles were more likely to cause vomiting, the team reports, and smaller toads were more likely to barf up the beetle). The regurgitated beetles were all alive and well after being ejected.
And how did some of these beetles survive nearly two hours inside a toad’s stomach? It turns out that bombardiers are also hardy. When the researchers compared them with other beetle species after 20 minutes in a stomach, the bombardiers were significantly less affected by the digestive juices.
“The strong acids in the gastric juices in the predators’ stomachs may kill the prey before vomiting them out. This suggests that bombardier beetle species may have evolved the ability to survive toads’ digestive system,” Sugiura said in an email.
The power of this strategy, Moore says, is that it not only increases the beetles’ odds of survival, but it also probably serves as a powerful deterrent for predators to contemplate snacking on a yummy beetle morsel ever again.