The Find So Big in the Animal Kingdom but Yet So Odd We Didn't Put It in the Headline

While role reversal is often a term tossed around to describe instances when males and females switch their traditional duties -- like men taking over childcare while women sit in the boardroom -- scientists recently announced one of the animal kingdom's most dramatic examples of a sexual role reversal.

Researchers studying Brazilian insects identified four species within the same genus where the sex organs were reversed -- females had penises.

"Although sex-role reversal has been identified in several different animals, Neotrogla is the only example in which the intromittent organ is also reversed," Kazunori Yoshizawa from Hokkaido University in Japan said.

This is what the sex organ in this genus of insects looks like. It has spines that anchor it to the male. (Image source: Current Biology, Yoshizawa et al.)

“It was a surprise for all of us,” Rodrigo Ferreira from the Federal University of Lavras in Brazil told National Geographic. “We were completely astonished when we first saw that structure.”

The observations of the cave-dwelling insects were published in the journal Current Biology. During the sexual act, which takes 40 to 70 hours, the researchers witnessed female insects with penises and males with vagina-like openings. The males still are the ones that contribute sperm during the act.

Neotrogla curvata copulating. (Image source: Current Biology, Yoshizawa et al.)

"It will be important to unveil why, among many sex-role-reversed animals, only Neotrogla evolved the elaborated female penis," Yoshitaka Kamimura from Keio University in Japan said.

Researchers think the cave environment could be what drove the physical role reversal over time. Ferreira, a co-author on the study, told NatGeo food sources -- bat feces and carcasses -- are scarce in the caves. This, he said, could have led to a female that has the ability to hang onto a male for a long period of time to get enough seminal fluid, which could be nutritious for developing offspring.