As the only mammals that can fly, bats are the oddballs of the mammalian world. But serotine bats stand out for another, glaringly obvious reason — when erect, a male’s penis can swell to almost a quarter of its body length. How these bats use their humongous genitals to mate — without penetration — is a method never seen in a mammal before, researchers report in the Nov. 20 Current Biology.
At more than 16 millimeters when erect, the penis of male serotine bats (Eptesicus serotinus) has no chance of fitting inside the female’s approximately 2-millimeter-long vagina, a discrepancy that prompted biologist Nicolas Fasel to wonder how these bats go about getting it on. Videos collected at the Ukrainian Bat Rehabilitation Center in Kharkiv from 2018 to 2021 and the attic of St. Matthias Church in Castenray, Netherlands, from 2016 to 2022 revealed the answer. With footage, taken from underneath the bats, “we could see actually what was happening,” says Fasel of the University of Lausanne in Switzerland.
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