Girls will be boys and boys will be girls, but a little-known Brazilian insect takes role reversal to a whole new level, scientists have learned.
The cave-dwelling Neotrogla female sports an impressive penis, which she uses to "mate" with her male partner.
He, on the other hand, is blessed with what the researchers describe as a "much-reduced, vagina-like opening".
As if that does not make the insect's sex life interesting enough, copulation between the two sexes can last up to 70 hours.
"Although sex-role reversal has been identified in several different animals, Neotrogla is the only example in which the intromittent organ is also reversed," said lead scientist Dr Kazunori Yoshizawa, from Hokkaido University in Japan.
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A study of four species of the Neotrogla genus showed that the penis-like structure of the female, called a gynosome, is inserted into males and used to receive capsules of nutrient and sperm.
Once within a male, part of the gynosome inflates and projects spines which anchor the two insects together.
The scientists found it impossible to pull coupling males and females apart without causing injury.
Their description of Neotrogla's strange mating habits is published in the journal Current Biology.
