Female insects have been discovered in Brazil with penis-like sex organs, that insert into a male to suck out sperm. The Neotrogla is said to be the first example of an animal with 'sex-reversed' genitalia.

Copulation between the cave-dwelling insects can last between 40-70 hours.

The female's complex reproductive structure - called a gynosome - is used to suck out sperm from the male's vagina-like opening.

Once inside a male, part of the gynosome inflates and projects spines which lock the two insects together.

The findings are published in the latest edition of 'Current Biology'.

"Females have a highly elaborate, penis-like structure, the gynosome, while males lack an intromittent organ" it says, adding that "Nothing similar is known among sex-role reversed animals".

The insects feed on bat droppings and possess what researchers have called an "evolutionary novelty".

Researchers from Hokkaido University in Japan say the females controlled the entire mating process.