KOBE -- After being swallowed alive by a frog, an aquatic beetle that inhabits paddy fields can escape from its captor's anus, a study by a researcher at Kobe University in western Japan has confirmed.
Shinji Sugiura, associate professor in ecology at the university's Graduate School of Agricultural Science, studies the escape behavior of insects so as not to be eaten by other animals. While some bugs escape from the mouths of predators, others come out from the anus of the animal that consumed them. In the latter case, the insects need to endure being inside the digestive tract for a long time, and it is apparently not known how they survive.
Sugiura experimented giving various insects to a frog that does not have teeth, and swallows its prey whole. The Regimbartia attenuata is a beetle that measures about 5 millimeters in length. He gave 15 of the beetles to a species of frog called Pelophylax nigromaculatus, and saw 14 of them come out of the frog's anus alive.
It takes about 50 hours on average for food to come out as feces after being eaten by the frog, but the beetles managed to escape in about 1.6 hours on average. The associate professor says the bugs could be stimulating bowel movements from the inside to encourage defecation.
According to Sugiura, he has tried the same experiment with about 50 other species of aquatic and terrestrial insects, but only the Regimbartia attenuata successfully escaped. He also experimented using four other different species of frogs, and recorded a success rate of over 60%.
Sugiura analyzed, "The beetles could be closing their hard forewings to protect themselves from digestive juices, and storing up oxygen inside their closed wings to endure a long period in an environment without oxygen."
Sugiura's findings were published in the international academic journal Current Biology on Aug. 4, which can be read at https://doi.org/10.1016/j.cub.2020.06.026.
(Japanese original by Kimi Sorihashi, Kobe Bureau)