In a groundbreaking study published in Current Biology, researchers have documented for the first time that sex without penetration is possible in mammals – specifically in serotine bats. The penises of male bats are about seven times longer than their female partners’ vaginas, making penetration impossible. Instead of functioning as a penetration organ, male bats use their oversized penises to move the female’s tail sheath away and maintain contact mating.

Nicolas Fasel, lead author of the study from the University of Lausanne, Switzerland, explained that this type of copulation had not been described in mammals before. “We think that perhaps it is like in the dog, where the penis becomes engorged so that it becomes stuck or perhaps they simply could not insert it,” said Fasel.

Researchers observed genitalia during copulation using images from cameras placed behind a grate that they could climb onto. They analyzed a total of 97 pairings from the Dutch church and Ukrainian center. Additionally, they studied the morphology of serotine bat genitalia by measuring erect penises of live specimens and performing necropsies on those that died. When erect, male serotine bats’ penises are about seven times longer and seven times wider than females’ vaginas.

This research raises new questions about other bat species’ reproductive practices and highlights the need for further research and observation methods to deepen our understanding of mating behavior in bats.