The Great Escape: Beetle Exits Frog Unscathed After Being Swallowed Whole

Researchers in Japan say in new study the aquatic beetle regimbartia attenuata actively stimulates the gut of the frog pelophylax nigromaculatus after being eaten in order to facilitate its escape through excretion. (Credit: Kobe University)

(CN) — For most prey, being captured by a predator means their life in the wild has ended. But some animals can survive an otherwise fatal encounter with a predator — even after being eaten — though the eventual escape isn’t exactly a clean one.

Some beings in the animal kingdom can evade predators while others can avoid stalking and attacks in the wild all together.

But for animals who end up in the unfortunate position of having been swallowed by a predator, hope is not lost. Some escape by passively making their way through predators’ digestive systems. In other words, they’re pooped out alive.

For the first time, researchers in Japan have documented the active escape strategy used by insects who have been eaten, according to the study published Monday in the journal Current Biology.

Kobe University ecologist Sugiura Shinji found that a frog’s “vent” provides the escape route for the aquatic beetle regimbartia attenuataafter it has been swallowed. The frog, scientific name pelophylax nigromaculatus, is one of many frog species that lack teeth and is therefore unable to kill their prey before swallowing them. This makes the frog’s digestive tract a critical player in breaking down swallowed prey.

In laboratory tests, researchers provided frogs with various insect species in order to observe their escape processes. 

“All adults were easily swallowed by the frogs,” the researchers said in a statement accompanying the study. “However, 93.3% of the swallowed beetles were excreted within 6 [hours] after being swallowed. Surprisingly, all excreted beetles were alive and active.”

Researchers found that the beetle regimbartia attenuatanot only escaped but can also stimulate the frog’s gut to promote the excretion process and therefore facilitate its liberation. 

“Because the frog’s sphincter muscle pressure keeps the vent closed, the tiny beetles are unable to exit through the vent without inducing the frog to open it,” the media statement said.

Researchers observed the same behavior when the aquatic beetle was swallowed by four other frog species: pelophylax porosus, glandirana rugosa, fejervarya kawamurai, and hyla japonica, the study said. 

The frog alwaysexcreted undigested parts of the prey it swallowed in under 24 hours, the study found.

Both the aquatic beetle and frog investigated in the study are found in the same paddy fields in Japan, the study said, adding that the frog frequently preys on other terrestrial and aquatic insects in the field.

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