First, a frog snags the beetle and gulps it down whole. For a tense 115 minutes, nothing happens. Then, the great reveal: the same shiny insect wiggles its way out of the amphibian’s anus, leaving both frog and beetle alive and seemingly no worse for the wear.
Sugiura, a researcher with Kobe University, tells Wired’s Matt Simon that he had been planning to study the predator-prey relationship between R. attenuata and the frog because they share a habitat in Japan’s rice paddy fields.
“However, I did not predict that R. attenuata can escape from the frog vent,” Sugiura tells Wired. “I simply provided the beetle to the frogs, expecting that the frogs spat them out in response to the beetles’ behavior or something.”
According to a Kobe University statement, this study marks the first time that researchers have witnessed prey quickly and actively escape the body of its predator after being eaten. Sugiura published his findings Monday in the journal Current Biology.
Sugiura first tested R. attenuata’s escape techniques with the frog Pelophylax nigromaculatus and found that a whopping 93.3 percent of the beetles were able to escape via the frog’s “vent,” or anus. He found that the beetles had similarly high success rates with four other frog species.
As Katherine J. Wu reports for the New York Times, the small beetles—iridescent black insects no longer than four or five millimeters across—were able to make the trip in a minimum time of six minutes. (The longest journey took about four hours, per Wired.) The beetles emerged out the other end covered in feces, but otherwise active and seemingly healthy.
Sugiura hypothesizes that the beetle may evolved this capability as an anti-frog defense tactic. When swallowed, other similar water beetles were killed and digested by the frog, reports Kristen Rogers for CNN.
The beetle has to make its way through several inches of inner organs, including an esophagus, stomach, small intestine and large intestine, per CNN. The digestive juices make for a deadly environment, so speed is imperative.
Because some beetles were able to complete the harrowing trip in six minutes, Sugiura concluded that the beetle was actively moving through the frog’s insides, rather than being passively transported. He tested this theory by immobilizing some of the water beetles’ legs, which are used to swim, with a sticky wax. None of the immobilized beetles survived, but rather were digested and excreted the usual way, per the New York Times.
“That was smoking gun evidence that they are using their legs,” Nora Moskowitz, an ecologist at Stanford University who studies frog digestion and who was not involved in the study, tells the Times.
Sugiura suspects that the beetles also use their legs to stimulate the frog’s cloacal sphincter, causing it to defecate. However, he’ll need to run more tests to be sure, reports Wired.
Sugiura has seen some other gnarly beetle escapes in his time: In 2018, he recorded bombardier beetles spraying a toxic chemical cocktail while inside a toad, which forced the amphibian to vomit the beetle back out alive.
“Frogs are voracious predators, forming an irreplaceable role in food webs and most ecosystems,” biologist Jodi Rowley, who was not involved in the research, tells Wired. “It would be interesting to see if the frogs avoided eating these beetles in the wild, or if they continue to consume them, with the occasional beetle that fails to pull off their escape making it all worthwhile.”
The frog doesn’t seem to be bothered by the little beetle’s journey through its insides, Sugiura points out. “However, I do not want to eat this beetle if I’m a frog,” he tells the Times.