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Some females have penises. Scientists discovered Brazilian cave insects are actually sex-revered- meaning that females mate by inserting their "penis-like organs" into males' "vagina-like" openings.

Researchers said the latest discovery on the Brazilian bugs, which represent four distinct but related species in the genus Neotrogla, is the first to find animals with sex-reversed genitalia.

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

Researchers explain that these insects mate for an impressive 40 to 70 hours, with the female pushing their "elaborate, penis-like organ into males' much-reduced, vagina-like opening," researchers wrote in a news release.

Researchers believe that this sex-role reversal may have evolved to cope with the resource-poor cave environment in which the insects live. Researchers explain that males in this genus give their female mates nutritious seminal gifts and sperm, which means that it is advantageous for females to mate at a higher rate.

Rodrigo Ferreira of the Federal University of Lavras in Brazil first discovered these insects. Ferreira then sent some specimens to Charles Lienhard, an insect-specialist in Geneva. The Swiss scientists then discovered that the specimens were actually a new genus, with females possessing very penis-like organs.

Afterwards, Yoshizawa and his team looked at the mating behavior of all four species. They find that the penis-like structure, termed the gynosome, is inserted into males and used to collect generous capsules of nourishment and sperm. They found that the membranous part of the female gynosome of "penis" inflates and numerous spines internally anchor the two insects together.

Disaster happened when researchers tried to pull a male and female apart. They found that the male's abdomen was ripped from the thorax. However, the genital coupling was still in place, meaning that females hold on to males very tightly.

Researchers said the next step is to study sexual selection, conflict between the sexes, and the evolution of novelty of these insects.

"It will be important to unveil why, among many sex-role-reversed animals, only Neotrogla evolved the elaborated female penis," concluded Yoshitaka.

The findings are published in the journal Current Biology.