For the first time, a mammal has been documented engaging in sex without penetration – specifically, the serotine bat, as revealed in a study published in Current Biology. The penises of bats are about seven times longer than the vaginas of their partners and have a head-heart shaped seven times wider than the vaginal opening, 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, from the University of Lausanne, Switzerland, and lead author of the study stated, “We think that perhaps it is like in the dog, in which the penis becomes engorged so that it becomes stuck, or perhaps they simply could not insert it, but that type of copulation had not been described in mammals until now.”

This study sheds light on very little known about how bats mate. Researchers observed genitals 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. They also observed that the female’s abdomen appeared moist after copulation, suggesting the presence of semen but more studies are needed to confirm sperm transfer.

The researchers characterized morphology by measuring erect penises of live specimens and performing necropsies on those who died. When erect, male serotine bat penises are about seven times longer and seven times wider than female vaginas of same species. This research will lead to further studies on mating behavior in natural contexts and studying penis morphology and bonding behavior in other bat species in future.

In summary this study has revealed never-before-documented mating behavior in mammals which raises new questions about other bat species and deepening our understanding about reproductive practices of serotine bats through further research and new observation methods is needed.