In a groundbreaking study published in Current Biology, researchers have documented for the first time that sex without penetration is possible in mammals. Specifically, they found this behavior to be prevalent in the serotine bat.
The penises of male bats are significantly larger than those of their female counterparts, with an average length of seven times the vaginal opening and a head that is seven times wider. This makes penetration impossible, and instead, male bats use their oversized penises to move the female’s tail sheath away during mating.
Nicolas Fasel from the University of Lausanne in Switzerland, lead author of the study, stated: “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. However, this type of copulation had not been described in mammals until now.”
Researchers observed genitalia during copulation using cameras placed behind a grate that they could climb onto and analyzed a total of 97 pairings from both Dutch church and Ukrainian centers. The female’s abdomen appeared moist after copulation, indicating the presence of semen. However, more studies are needed to confirm that sperm was transferred.
The researchers also characterized the morphology of serotine bat genitalia by measuring erect penises on live specimens and performing necropsies on those that died. When erect, their penises are about seven times longer and seven times wider than the vaginas of females. They plan to study mating behavior in more natural contexts and explore penis morphology and bonding behavior in other bat species in future research endeavors.