Scientists have discovered a new species in which the female is the individual who has the penis and the male has a vagina-like opening. According to Kazunori Yoshizawa—from Hokkaido University in Japan—these cave insects are the only documented beings in the planet with this surprising feature.

Although sex-role reversal has been identified in several different animals, Neotrogla is the only example in which the intromittent organ is also reversed.

The research—published in the April 17 issue of Current Biology—describes four related species in the genus Neotrogla about 4 millimeters long, discovered in 2010 by Rodrigo Ferreira in a Brazilian cave.

According to their observations, the female introduces her penis—called gynosome—deep into the male's opening in a copulation that lasts 40 to 70 hours. The female, as shown in this image, is always on top. In exchange for the female impregnating them, the males provide with "nutritious seminal gifts."


A close-up of the terminal abdomens in copula, as seen from the side.

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