For the first time, scientists have discovered animals whose genitalia seem to be swapped: The female has a penis-like structure while the male has an organ akin to a vagina, LiveScience reports. The animals in question are four species of flea-sized insects from the genus Neotrogla, found in Brazilian caves. Mating between the creatures is far from rushed: It lasts between 40 and 70 hours, and sees the female inserting her gynosome (what the penis-like organ is being called) into the male's vagina-like phallosome to retrieve a teardrop-shaped sperm capsule. The gynosome is a "completely novel structure in evolution," says Kazunori Yoshizawa, lead author of the study, published in Current Biology.
The gynosome features spiky spines that link males and females together during copulation—a link so strong that scientists trying to pull them apart ended up ripping out a male's abdomen. And that's something seemingly remarkable about Neotrogla. They've developed what Nature calls a "sex-role reversal," where the males are selective and the female is the aggressor, able to "coercively grasp and copulate with a reluctant male," says Yoshizawa. And while some animals (like seahorses and mites) have reversed sex roles, no females have those coercive "grappling hooks." This could be because the males' capsule offers more than just sperm. It may provide sustenance the female needs in the food-scarce cave environment—hard-won nutrients the male is reluctant to provide to just any mate. One other wild fact: The insects measure no more than 3.7 millimeters, with the gynosome measuring up to 0.5mm; that's equivalent to a 5-foot 9-inch human having a 9.8-inch penis. (Also fascinating: Why human penises no longer have spikes.)