Bats, a species that inhabits most of Europe, including the Iberian Peninsula, have an unusual way of mating. Due to their disproportionately large penis, which is seven times longer than the female vagina and has a heart-shaped head that is seven times wider than the vaginal opening, penetration after erection is impossible. Instead, bats use their large penis as an extra arm to push against the female’s tail membrane.

In this non-penetrative way of mating, bats are able to mate by contact, a behavior that resembles the ‘cloacal kiss’ of birds. This is the first time that non-penetrative sex has been documented in a mammal. The discovery was made by an international team of researchers who observed bats in their natural habitat and analyzed videos from cameras placed behind a grate that the bats could climb onto. The team analyzed 97 mating acts: 93 from a church attic in the Netherlands and four from a rehabilitation center in Ukraine.

During mating, male bats grabbed their mates by the back of the neck and moved their pelvises (and fully erect penises) in a probing fashion until they made contact with the female’s vulva. Then they stayed still in a long embrace. On average, these interactions lasted less than 53 minutes, but the longest event lasted 12.7 hours. The researchers noted that females’ abdomens appeared moist after copulation, suggesting the presence of semen, but more research is needed to confirm that sperm was transferred during these supposed mating events.

The morphology of bats’ genitalia was also characterized by measuring erect penises of live specimens captured as part of other research studies and performing necropsies on specimens that died in rehabilitation centers. Their measurements showed that when erect, bats’ penises are about seven times longer and seven times wider than female vaginas, reaching about one-fifth of their head-to-body length (about 7 centimeters). Females also have unusually long cervixes, which could help them select and store sperm.

The team speculates that bats may have evolved their oversized penises to push away female tail webbing, which they can use to avoid sexual intercourse. “Bats use their tail membranes to fly and capture insects,” says Fasel