The serotine bat has some frankly astounding sexual behaviour (Picture: PA)

Here’s a story you weren’t expecting on a Monday afternoon – a British bat uses its penis as an extra arm during sex. For up to 12 hours.

The serotine bat, or Eptesicus serotinus, appears to mate without penetration because its penis is around seven times longer and wider than the females’ vagina, making ‘traditional’ methods of reproduction physically impossible.

Instead, scientists believe the bats, which are found across Europe, use their large apparatus to push the female’s tail sheath out the way so they can engage in ‘contact mating’, a behaviour that more closely resembles how birds reproduce but never seen before in mammals.

Little is known about the sex lives of bats given their elusive and nocturnal lifestyles, but after getting a sneak peek, researchers at the University of Lausanne were surprised by what they witnessed.

‘By chance, we had observed that these bats have disproportionately long penises, and we were always wondering, “How does that work?”,’ said first author Nicolas Fasel, of the Swiss university.

‘We thought maybe it’s like in the dog where the penis engorges after penetration so that they are locked together, or alternatively maybe they just couldn’t put it inside, but that type of copulation hasn’t been reported in mammals until now.’

The serotine bat is found across Europe, including in Britain (Picture: Alona Shulenko)

Experts say most previous observations of bats mating have only perceived the backs of mating pairs.

In the new study, researchers were able to observe the bats’ mating process in more detail by using footage from cameras placed behind a grid the animals could climb on.

The researchers did not observe penetration at any point during the recorded mating events.

According to the findings, during mating the male bats grasped their partners by the nape and moved their pelvises – and fully erect penises – in a probing fashion until they made contact with the female.

At this point they remained still and held the females in a long embrace.

On average, these interactions lasted less than 53 minutes, but the longest event extended to 12.7 hours.

Following the bat lovemaking, researchers observed that the female bats’ abdomens appeared wet, suggesting the presence of semen, but further research is needed to confirm exactly what went on.

The bat behaviour is similar to when birds mate (Picture: Getty)

The team suggests the bats may have evolved their oversized penises in order to push aside the female bats’ tail membranes, which females may use to avoid sex.

‘Bats use their tail membranes for flying and to capture the insects, and female bats also use them to cover their lower parts and protect themselves from males, but the males can then use these big penises to overcome the tail membrane and reach the vulva,’ said Professor Fasel.

The researchers collaborated with a bat rehabilitation centre in Ukraine, which opportunistically filmed mating pairs, and with a bat enthusiast and citizen scientist, Jan Jeucker, who filmed hours of footage of serotine bats in a church attic in the Netherlands.

Altogether, the team analysed 97 mating events – 93 from the Dutch church and four from the Ukrainian bat rehabilitation centre.

The study is published in the Current Biology journal.

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Just when you thought nature couldn’t get any more bizarre.