Female insects in Brazilian caves initiate reproduction, and they do so with a penis.

Kazunori Yoshizawa at Hokkaido University in Sapporo, Japan, and his colleagues studied four Neotrogla species, one of which copulates for up to 70 hours. The authors found that the female uses an external organ (pictured) during sex to penetrate the male and to receive sperm for both reproduction and nutrition. All of the species have spines on the penis-like structure, which the females use to anchor themselves in the male genital chamber.

The competition between females for mates might have driven the evolution of this elaborate sexual structure, the authors say. However, this is the only known case of reversed sex organs in animals with reversed sexual roles, they add.

Credit: Yoshizawa et al./Current Biology

Curr. Biol. http://dx.doi.org/10.1016/j.cub.2014.03.022 (2014)

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