The orchard bat, also known as the Eptesicus serotine, has a disproportionately large penis in comparison to the female’s vagina. This makes penetration impossible, leading researchers to discover that bats use their large penis as an extra arm to push against the female’s tail membrane, allowing them to mate by contact.
The researchers analyzed 97 mating acts and did not observe penetration at any time. They noted that male bats grabbed their mates by the back of the neck and moved their pelvises in a probing fashion until they made contact with the female’s vulva. After copulation, the females’ abdomens appeared moist, suggesting the presence of semen, but more research is needed to confirm that sperm was transferred during these supposed mating events.
The team also studied the morphology of the bats’ genitalia and measured the erect penises of live specimens as well as performing necropsies on specimens that died in rehabilitation centers. They found that bats’ penises are about seven times longer and seven times wider than female vaginas, reaching about one-fifth the bats’ head-to-body length.
The discovery adds a new chapter to the curious sexual life of bats, which includes oral sex and ‘prostitution’ behavior. The researchers now plan to study bat mating behavior in more natural contexts and investigate penis morphology and mating behavior in other bat species. They aim to develop a “bat porn box” as a research tool.