There Are Two Ways Out of a Frog. This Beetle Chose the Back Door.

“That was smoking gun evidence that they are using their legs,” said Nora Moskowitz, who studies frog digestion at Stanford University but wasn’t involved in the study.

Dr. Sugiura thinks Regimbartia beetles may use their legs to brace themselves and crawl through the gut, which can stretch several inches — an arduous journey for a four- or five-millimeter-long beetle. When they reach the end of that tunnel, the insects may be able to tickle open the cloacal sphincter, the ring of muscle that drawstrings the frog’s rear end shut, expelling themselves in a flood of feces.

A trek through this passage probably isn’t trivial, said Aurora Alvarez-Buylla, a frog researcher at Stanford University who wasn’t involved in the study. Because frogs swallow their prey whole, their digestive juices have to be potent. “You’re dealing with a chemical and acidic environment that is built to pull things apart and break them down,” she said.

But as far as Dr. Sugiura could tell, the insects were entirely unfazed by their tortuous trip through the tract. Once liberated, they simply extracted themselves from the dung and swam happily onward. Months later, some of the bugs were still kicking about as if the traumatic encounter had never even happened.

The insects’ resilient outer casing, or exoskeleton, might help. But a few repeat trips down a frog’s gullet could eventually take a toll, Dr. Sugiura said. More experiments are needed, he said, to understand how it all comes out in the end.

The frogs, too, seemed to depart the encounter unscathed. According to Dr. Sugiura, amphibian waste is often studded with the hard body parts of prey.

“However,” he said, “I do not want to eat this beetle if I’m a frog.”

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