The secret sex lives of bats: Study reveals how males have penises 7 times longer than their partners' vaginas - and use them as an 'arm' during romps that can last up to 12 HOURS

In humans, the erect penis has only one function – but elsewhere in the animal kingdom it serves a very inventive purpose. 

Scientists say the male serotine bat uses its massive phallus as an 'extra arm' to move part of the female's anatomy out of the way. 

This allows them to engage in contact mating for up to an incredible 12.7 hours before the male climaxes.

The bat penis is about seven times longer than their partner's vagina and has a 'heart-shaped' head seven times wider than the vaginal opening, so conventional penetrative sex could damage the female. 

Very little is known about how bats have sex, although previous research has shown certain bat species emit a peculiar 'perfume' to find a mate.

The new study was conducted by experts at the University of Lausanne's Department of Ecology and Evolution in Switzerland. 

It describes the first known example of non-penetrative sex in a mammal, they claim.

'By chance, we had observed that these bats have disproportionately long penises, and we were always wondering "how does that work?",' said Professor Nicolas Fasel, first author of the study. 

'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 researchers speculate that 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,' said Professor Fasel.

'But the males can then use these big penises to overcome the tail membrane and reach the vulva.' 

The serotine bat (Eptesicus serotinus) is found throughout Asian and Europe, including the southern half of the UK, according to the Woodland Trust. 

The species lives in open woodland, hedgerows, parkland, and pastures but when it hibernates in the winter it can be found taking shelter in old buildings, such as disused chimneys and inside walls. 

To learn more about the secret sex lives of the species, researchers set up cameras at two locations – a church attic in the Netherlands and a bat rehabilitation centre in Ukraine. 

The experts were able to get close-ups of the bat genitalia during sex by placing cameras behind a grid that the bats could climb on. 

Altogether, the team analysed video footage of 97 mating events, which all revealed that the little mammals do not engage in penetrative sex. 

The researchers did not observe penetration at any point during the recorded mating events, although what they did observe was illuminating. 

During mating, the male bat would grasp their female partner by biting her neck and moving their pelvis (and fully erect penis) in a 'probing' fashion.

Only once he had made contact with the female's vulva, the male remained still and held its partner in a long embrace. 

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

'During this time we noted several social calls, probably emitted by the female,' the study authors say. 

Following copulation, the female bats' abdomens appeared wet, suggesting the presence of semen, but further research is needed to confirm that sperm was transferred. 

Female bats seem to use this strategy to choose the suitable mate to parent their offspring, even after the deed has already been done.

'We still don't know the mechanism behind this,' Fasel says. Therefore, this post-mating selection is appropriately called 'cryptic female choice.' 

'In terms of evolution, this is also quite interesting because sexual selection has driven the evolution of incredible traits,' Fasel says. 'It's really crazy.'

The females have unusually long cervixes, which could help them select and store sperm, but more research may be needed. 

'This study reveals a novel copulatory pattern in mammals and introduces an interesting research model,' the team concluded. 

'Indeed, further investigation should focus on the role played by pre- and post-copulatory female choice as well as male competition in the evolution of this prolonged and particular mating behaviour.' 

The paper has been published in Current Biology.