Bats with penises that measure over 20% of their body length don't make babies like any other mammals, according to a new study

• By chance, researchers noticed that one bat species had a very large penis.
• This led the scientists to question how the species mate, which led to a shocking discovery.

For one species of bats, bumping uglies has just taken on a whole new meaning.

A group of scientists observed a population of serotine bats in Europe and found that these animals are the only mammals that don't mate via penetration, according to a press release from the American Association for the Advancement of Science.

Instead of putting his penis inside the vagina, the male bat just sticks his part near the female's opening and holds it there until the job is done.

This behavior is well known in birds, but it's the first time ever that it's been observed in a mammal, the researchers said in their study, published in the peer-reviewed journal Current Biology.

How, you might ask, did scientists get here?

Bats with shockingly giant penises

Well, when the scientists put the bats under anesthesia to learn more about their reproductive biology, they noticed that the males were incredibly well-endowed, Nicolas Fasel, lead author of the paper from the University of Lausanne, told Business Insider.

Fasel explained that the sheer size and shape of the organ were shocking to them. "When we just had to anesthetize the bats, we could see their erection. And then we were just like, 'Wow. What is that?'"

When erect, the bats' penises were on average 0.65 inches long. That might sound small, but for an animal that's only 2.44 to 3.15 inches long, it's actually 22% of their body length, the researchers reported in the study.

(It would be the equivalent of a six-foot-tall human male having a penis that, when erect, grew to be slightly over 15 inches long.)

In fact, the researchers explained in the paper, the male bat's penis is seven times longer and wider than the female bat's vagina.

So how does a species reproduce when they have a square peg and round hole situation? That's what the scientists simply had to find out, Fasel said.

A scientific peep show and future bat porn box

Serotine bats are found all over Europe, according to Animal Diversity Web. This study focused on a population of bats living in the attic of a Dutch church and in a bat rehabilitation center in Ukraine.

People at the church and rehab center were observing the bats using cameras set up under a grid that the animals could climb on. Fasel and his team obtained the footage and scanned through it specifically for mating examples, and they weren't disappointed.

The researchers observed 97 mating rituals. Each time, instead of putting its penis inside a partner's vagina, the male bats used it as a sort of arm, to move the female bat's tail membrane out of the way for easy access to the vaginal opening.

Then, the male bat held the female in an "extended embrace". In one particularly impressive case, it went on for 12.7 hours.

Moving forward, Fasel told BI that the researchers want to make an even more comprehensive viewing theater to observe the bats. By doing so, they can observe all sides of the bat's environment to try and understand how they reproduce in nature.

"We are trying to develop a bat porn box, which will be like an aquarium with cameras everywhere," Fasel said in the press release.