Gender-bending insect species discovered in Brazil

A close-up of a female in the species N. aurora
Current Biology, Yoshizawa et al.

Four new species of bugs discovered in Brazil defy the laws of gender: the females have penises, the males have vaginas.

And these are no typical penises; they feature spikes that anchor the female into the male. During their 70-hour marathon mating sessions, they work like vacuum cleaners, sucking sperm out of the male vaginas.

"There's nothing that [this] can be compared to," study co-author Rodrigo Ferreira told National Geographic. "This elaborate female penis is completely unique." His research was published April 17 in the journal Current Biology.

A cave specialist at the Federal University of Lavras in Brazil, Ferreira collected the bugs in the caves of eastern Brazil in 2010 and sent them on to a lab at the Museum of the City of Geneva in Switzerland, where Charles Lienhard quickly determined that these species belonged to a new genus of insect. They named it Neotrogla.

The first clue that these flea-sized species were unique came in the way they mate: the female is always on top, probing its penis-like organ into the male.

Closer observation determined that the organ, which the researchers dubbed a "gynosome," is prickly. On three of the species, it has spines; the gynosome of the fourth species has small bristles. The spines fit perfectly into small pockets in the walls of the male's vagina.

A third researcher, Kazunori Yoshizawa of Hokkaido University in Japan, attempted to pull a male and female pair apart as they were mating. The male ripped in two, while the female stayed put.

From this, he determined that the penis spikes and bristles are designed as an anchor to keep the male in place. New Scientist points to the spikes as a reason why the scientists have not seen the males resist mating: it would physically hurt them, possibly even rip them in two, if they tried to stop the female in the middle of the act.

In the study, Ferreira's research team explained that females of several mite and beetle species use long, tube-like protrusions to mate, but none of these feature anchoring spikes like those on the new species. Female seahorses use a protruding appendage to deposit eggs in the male pouch, "but this is not a penis," they wrote.

How these four species evolved to have female penises remains to be determined. Yoshizawa told New Scientist that they could be a by-product of living in caves with a low food supply.

The pockets where males store sperm also contained nutrients, Yoshizawa observed when he dissected the males. The females do not have these pockets, so they could have developed the penises as a way to also extract nutrients from the males.

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    Danielle Elliot is a freelance science editor and reporter for CBS News. She holds an M.A. in science and health journalism from Columbia University and a B.A. in broadcast journalism from the University of Maryland. Follow her on Twitter - @daniellelliot.