The females have a penis and the males have a vagina in several species of insects that scientists discovered in Brazil.
The insects, called Neotrogia, were discovered in a cave in the Peruacu River Valley in Brazil, reports The Verge. A study of the insects was published in the journal Current Biology.
"The female penis is a completely novel structure," said study co-author and entomologist at Hokkaido University Yoshizawa Kazunori. The female Neotrogia evolved to become "very masculine."
The reason the females are considered females at all despite sporting a penis, is because biologists focus on the size of the animal's gametes and not their sex chromosome. In Neotrogia, the females have the larger gametes, oocytes, compared to the male's, sperm. Plus she takes sperm from the male to fertilize her eggs.
Copulation between the male and female Neotrogia, much like the female's penis (1/7th their size), is quite long, reports NBC News. The process can last between 40 and 70 hours, during which spines within the female's penis keep her attached to the male.
Yoshizawa said, "It is very likely that female Neotrogia can coercively grasp and copulate with a reluctant male." He added, "In animals, coercive mating is generally an exclusive feature of males."
The discovery of the four species of Neotrogia is exciting, Yoshizawa explained, as "usually, a new structure evolves as a modification of a previously existing structure," but as far as they know, this doesn't have one.