The common serotine bat (Eptesicus serotinus) mates without penile penetration: the male uses his unusually shaped penis as a “copulatory arm,” moving past the female’s tail membrane to make contact with her vulva. A 2023 study documented this behavior in this species; it should not be treated as typical of bats generally.
How does a serotine bat mate without penetration?
In the behavior described by the study, the male mounts the female from behind. Rather than inserting his penis into her reproductive tract, he uses it to get around the female’s flight membrane and press it against her vulva. The researchers describe the penis as a “copulatory arm” rather than an intromittent organ.
The observations were made in a church attic and at a bat rehabilitation centre. The institute account reports live observations of nearly a hundred pairs, but does not clarify how many pairs contributed to the published analysis. It also says a pair may remain in position for several hours; that is a reported possibility, not an average or established duration for every mating.
Why is the penis described as heart-shaped?
Bat Conservation International reports that the male common serotine’s penis averages 16.4 mm long, with a heart-shaped terminal bulge averaging 7.5 mm wide. The female genital tract averages 2.3 mm long, according to the same source. These figures are reported by Bat Conservation International; the consulted page does not state a year, and they are not independently checked here against the original paper’s measurement table.
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The unusual shape and the female’s flight membrane help explain the mechanics: the male’s penis is used to reach the vulva rather than to penetrate the genital tract. The available accounts do not establish that the shape evolved for a particular purpose, so it is safer to describe the observed role than to claim a definitive evolutionary explanation.
What did the 2023 study establish?
The paper, “Mating without intromission in a bat,” was published in Current Biology, volume 33, issue 22, on 20 November 2023. Its abstract reports that in common serotine bats the penis functions as a “copulatory arm” rather than an intromittent organ. The authors present it as a novel copulatory behavior in mammals.
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That finding is specifically about Eptesicus serotinus. It does not show that all bats mate this way, nor does the report justify a sweeping claim that no other mammal has ever transferred sperm without intromission.
Independent reader supportYour contribution helps us test, update, and keep practical guides available for everyone.Do other bats mate the same way?
No single mating pattern applies to all bats. Published reports describe different behaviors in other species, including lek courtship in wrinkle-faced bats and oral-genital behavior in greater short-nosed fruit bats. These examples are distinct behaviors in distinct species, not variations that should be conflated with the serotine bat’s reported mating without intromission.
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