Ed Yong reports on a species of insect where the female has the penis and the male has a vagina.

Neotrogla mating.

Ed writes:

This picture of two mating insects comes with an unexpected twist. The one on top is a female, and she has a penis. The one on the bottom is a male, and he has the equivalent of a vagina. During sexual bouts that can last for 40 to 70 hours, she penetrates him and uses her genitals not to deliver sperm, but to collect it.

The 3-millimetre-long species is called Neotrogla curvata, and it lives in Brazilian caves. There are four Neotrogla species and the females all have penises. They belong to a group of insects called barkflies or barklice—closely related to lice and true bugs, and only distantly related to actual flies.

…

Neotrogla’s set-up is very different. The female has a penis-like protrusion called a gynosome, which is erectile and curved. The male has no such organ; he has an internal chamber instead. When she penetrates him during sex, he delivers sperm into a duct in her gynosome, which leads to a storage organ. He still ejaculates, but he does so inside his own body, not hers.