Bat sex can be a little kinky. When the winged mammals aren't going at it on football fields packed with thousands of spectators, they're engaging in lengthy bouts of oral sex in front of research cameras. And don't even get us started on the penis spines.

Scientists are still learning the ins and outs of bat mating – a task that can be tricky as the action usually happens under the cover of darkness in an inaccessible roost hidden from prying eyes. But sometimes, if you're really lucky, bat sex just falls right out of the sky.

While enjoying the view of Cayuga Lake in New York from a landing, Atlas Obscura staff writer Sarah Laskow heard a thud and noticed a ball of fur and wings lying on the concrete just a few feet away.

The twitching bat-ball appeared to be headless, and Laskow initially suspected that she may be witnessing one bat trying to eat another. When the video was shown to experts, however, they all agreed: these bats were caught in the act.

The copulating couple were Eastern red bats, and their sex life goes something like this ... It starts when the rusty-coloured male clasps onto the smaller, grey female by hooking his claws over her wings. As far as we know, this happens during flight –and reports suggest the bats are sometimes so focused on the deed that they forget to flap and simply fall out of the sky (which offers some explanation for the pair that thumped down in front of Laskow).

But wait, it gets even more interesting. The males in many bat species come equipped with spiked penises. Typically, these penis spines match the size of the bat: the bigger the bat, the bigger the penis, the bigger the spines. However, in the case of some tree-roosting species like the hoary bat (or the eastern red bat featured above), the spikes are outrageously large.

In a study examining the penis spines of bats (some researchers have all the fun), Teri Orr of the University of Massachusetts Amherst discovered that hoary bats win the size battle by some margin. Each of those penis spines is a rather alarming one centimere (0.4 inches) long. To put that into perspective, these relatively small bats have a nose-to-tail length of only about 15 centimetres (6 inches). That means their penis barbs are equivalent to about 6,6 percent of their entire bodies. If the average American man sported similar wedding tackle, his penis spines would be about 11.6 centimetres (4.5 inches) long (but it's not the size that counts, right?). Eastern red bats have similarly outsized man spikes.

The penis spines of an eastern red bat (Lasiurus borealis). Image: Teri Orr

So what do the bats do with these mace-like appendages? Scientists suspect the backwards-facing penis spines work like fish hooks to ensure the couple stays fused together during ambitious bouts of aerial coitus. It's called the "in-flight locking hypothesis", and although it's not yet proven, there are enough anecdotal records of entwined bats plummeting to the ground to suggest it's very plausible.

Unfortunately, the high-flying sex habits of tree-roosting bats could pose a treat to their survival. When Paul Cryan of the United States Geological Survey in Colorado noticed that tree-roosting bats were among the most common species to turn up dead near wind turbines, he set out to study what could be causing the fatalities.

It's possible, according to Cryan, that wind turbines resemble the perfect lofty launchpad as the bats seek out tall trees and high roosts come breeding season. Sadly, the flying mammals often end up colliding with the spinning blades, or develop bleeding lungs from the rapid decrease in air pressure around the turbines. Conservationists are still pushing for changes in industry practices to reduce bat deaths.

Of course, not all bats mate in mid-air. In the small number of bat species we've actually witnessed mating in the wild, most of the sex happens on ground level. But that doesn't make it any less freaky. Take the oral sex-loving short-nosed fruit bats from Southeast Asia for instance. A study published in 2009 describes how females of the species will often lick their partners’ … er … bat bits during mating. According to the research, the behaviour prolongs the action and scores the lady bats an extra 100 seconds of sex.

The roles seem to be reversed for Indian flying foxes, where males perform the extracopulatory favours. Although researchers are not yet sure what purpose oral sex serves for the bats, possible explanations range from "disinfection" to picking up chemical cues to gauge whether a partner is a good choice. Or perhaps they just enjoy it. We'll leave it to scientists to figure that one out.

So there you have it … bats perform oral sex, they have barbed penises, they do it on the ground, in the air, on football fields. And sometimes when bats have sex, they don't really look like bats, and the sex doesn't really look like sex.


Header image: Matthew O'Donnell; Homepage image: OZinOH