Scientists are bugging out over this gender-bending insect!

Japanese researchers discovered a penis on the tiny female Neotrogla bug, which uses her appendage to penetrate her male partners during sex, according to a study that won the eggheads a coveted prize this week.

The bug, a Brazilian cave-dweller, could change the definition of “penis” entirely — at least among entomologists, Asahi.com reported Friday.

The insects which were registered as a new species in 2010, measure a tiny 3 millimeters.

But the role-reversing lady bugs are long on lust: One mating session can last for up to 40 to 70 hours, scientists say.

Hokkaido University scientists, who made the discovery, were awarded the Ig Nobel biology prize for the genitalia discovery Thursday, according to the Japanese media site.

Ig Nobel Prizes are awarded for research that “makes people laugh and think,” according to their Web site.

The prize-winning scientists include Kazunori Yoshizawa of Hokkaido University and Yoshitaka Kamimura, associate professor at Keio University.