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Sunday, July 25, 2021

Bizarre: Escape through the “back exit”

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The water beetle crawls through the intestines of a frog and exits from the back.

Unusual survival strategy: A small water beetle from Japan survives even being devoured by a frog. As this video documents, it emerges two hours later undamaged and alive – from the frog’s back. As tests have shown, the little one crawls through the entire digestive tract of the frog to the “back exit”. 

This is the first case of such an active escape from the intestines.

Normally, being eaten means death for a prey animal. Even if it survives the mouth and teeth of the predator, it becomes fatal in the digestive tract at the latest. Corrosive digestive juices, decomposing enzymes, and lack of oxygen make a longer survival almost impossible. The predator’s digestive system kills almost any prey after ingestion, explains Shinji Sugiura of Kobe University.

Back exit

But there are exceptions – and Sugiura has now observed a particularly bizarre one. For his study, he had fed the frog Pelophylax nigromaculatus, which is found in Japanese rice fields, with various insects. Among the prey animals was Regimbartia attenuata, a four to five-millimeter water beetle also living in the rice fields. The frog also devoured these beetles without any problems.

But then something surprising happened: the eaten water beetle suddenly reappeared – from the frog’s back.

“Around 90 percent of the swallowed water beetles leaked in this way and, surprisingly, were still alive,” reports Sugiura. Regimbartia attenuata succeeds in this trick not only with this one frog species but also with four others, as the researcher found out through feeding tests.

Crawled through the intestines

But how does the Beetle manage this feat? Additional tests showed: If the legs of the water beetles are glued, they will not survive the intestinal passage. Instead, they die and their remains are normally excreted in the faeces after a day or two. Sugiura concludes from this that the water beetles actively crawled through the digestive tract to the “back exit” in order to accelerate their escape.

“This is the first documented case of such an active escape of prey from the belly of a predator,” states the biologist. 

The water beetle seems not only to actively crawl through the intestines, but also to manipulate the stool of its “host”. Because normally the muscle ring on the frog’s back ensures that the anus remains tightly closed.

The beetle could not overcome this barrier on its own. In order to get outside, it, therefore, stimulates the frog – possibly through tactile stimuli – to give up faeces.

 As soon as the anal ring opens, the little beetle crawls outside.

Source: Kobe University | Image Credit: iStock

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