For the first time, a mammal has been documented to mate 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.”

The study 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. The researchers 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 also characterized the morphology of serotine bat genitalia by measuring erect penises of live specimens and performing necropsies on those that died. When erect, penises are about seven times longer and seven times wider than vaginas. The researchers plan to study mating behavior of these animals in more natural contexts and also study penis morphology and bonding behavior in other bat species in future research.

In conclusion, this study has shed new light on never-before-documented mating behavior in mammals by revealing serotine bats’ reproductive practices. This research raises new questions about other bat species’ mating behaviors and further investigation is needed to deepen our understanding of these fascinating creatures’ reproductive habits.