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Remarkable determination not to be digested. It's said to be an example of 'exaptation', whereby physical adaptions were evolved in response to one environmental factor but turned out to aid survival for another reason.
Eaten water beetles stay alive by escaping through the predator's anus
By Kristen Rogers, CNN
Updated 1500 GMT (2300 HKT) August 3, 2020
[...]
The pressure of being hunted is typically what leads to the evolution of different escape behaviors in prey animals. Surviving the extreme conditions of an animal's digestive system is a wild card that depends on the prey animal's ability to move quickly through to the, ahem, escape hatch.
Such a deadly environment could impose speedy and active escape behaviors on swallowed prey species — so Shinji Sugiura, the author of the study, tested this hypothesis with aquatic beetles and dark-spotted frogs.
After the frogs swallowed the beetles, 90% of the insects were excreted within six hours of being eaten "and, surprisingly, were still alive," said Sugiura, an associate professor in the department of agrobioscience at Kobe University in Japan, in the study.
[...]
The dark-spotted frog's digestive system is a long, tube-like structure that consists of an esophagus, stomach, small intestine and large intestine. It starts at the mouth and ends at the vent (anus), just like a human. Since killed water beetles (with their legs fixed) took more than a day to exit the frog and the surviving water beetles took a successful minimum of six minutes, Sugiura concluded that the latter's exit must have been an active escape rather than dependent on the frog's waste.
"R. attenuata cannot exit through the vent without inducing the frog to open it because sphincter muscle pressure keeps the vent closed," Sugiura said. "R. attenuata individuals were always excreted head first from the frog vent, suggesting that R. attenuata stimulates the hind gut, urging the frog to defecate."
Much more detail on the experiment:
https://edition.cnn.com/2020/08/03/world/water-beetle-escape-from-predator-scn/index.html
Eaten water beetles stay alive by escaping through the predator's anus
By Kristen Rogers, CNN
Updated 1500 GMT (2300 HKT) August 3, 2020
[...]
The pressure of being hunted is typically what leads to the evolution of different escape behaviors in prey animals. Surviving the extreme conditions of an animal's digestive system is a wild card that depends on the prey animal's ability to move quickly through to the, ahem, escape hatch.
Such a deadly environment could impose speedy and active escape behaviors on swallowed prey species — so Shinji Sugiura, the author of the study, tested this hypothesis with aquatic beetles and dark-spotted frogs.
After the frogs swallowed the beetles, 90% of the insects were excreted within six hours of being eaten "and, surprisingly, were still alive," said Sugiura, an associate professor in the department of agrobioscience at Kobe University in Japan, in the study.
[...]
The dark-spotted frog's digestive system is a long, tube-like structure that consists of an esophagus, stomach, small intestine and large intestine. It starts at the mouth and ends at the vent (anus), just like a human. Since killed water beetles (with their legs fixed) took more than a day to exit the frog and the surviving water beetles took a successful minimum of six minutes, Sugiura concluded that the latter's exit must have been an active escape rather than dependent on the frog's waste.
"R. attenuata cannot exit through the vent without inducing the frog to open it because sphincter muscle pressure keeps the vent closed," Sugiura said. "R. attenuata individuals were always excreted head first from the frog vent, suggesting that R. attenuata stimulates the hind gut, urging the frog to defecate."
Much more detail on the experiment:
https://edition.cnn.com/2020/08/03/world/water-beetle-escape-from-predator-scn/index.html
