According to new research, vampire bats form social bonds by sharing freshly drained blood with unfamiliar members of their roost.

A vampire bat, possibly regurgitating partially digested blood for his companion. Vampire bats often share their blood meals. Luis Lecuona / USDA International Services

In a new study published in the journal Current Biology, the behavior is described as “visually resembling a sort of French kiss.”

It might sound desperately gross at first, but what this behavior actually shows is that vampire bats are extremely social animals.

“Food sharing in vampire bats is like how a lot of birds regurgitate food for their offspring. But what’s special with vampire bats is they do this for other adults, eventually even with some previous strangers,” Gerald Carter, professor at Ohio State University and lead author of the new study said.

Vampire bats need to feast on blood every three days or they run the risk of starvation, so the food-exchanging could also be a life-saving activity.

A Common Vampire Bat, Desmodus rotundus, feeding on a pig. Showcase of taxidermied animals, Natural History Museum, Vienna. Image credit: Sandstein

The researchers closely studied a group of vampire bats (Desmodus rotundus) made up of two different roosts from geographically separate locations. This meant many of the bats were unfamiliar with each other, heightening the need for some blood-sharing bonding.

Over the course of 15 months, the team documented how unfamiliar pairs would start to groom one another, a common social behavior observed in other species like primates. Fur grooming helps to remove nasty parasites from the bats’ skin and slows the spread of disease, but the researchers believe this behavior has a much deeper purpose.

“Even if you remove all ectoparasites from their fur, they still groom each other more than necessary for just hygiene,” adds Carter. “We think of social grooming as a kind of currency – a way to gain tolerance and bond with another individual.”

After getting a little more comfortable with each other, the bats would eventually move onto exchanging blood meals via the mouth. In fact, almost 15 percent of the bats were seen indulging in this behavior with a previously unfamiliar partner.

Image credit: Oasalehm/Wikimedia Commons

A strategic behavior to test out a potential friend or mate before fully committing to a relationship could explain why vampire bats began their bonding through grooming before shifting to a more substantial ritual like blood meal sharing. There’s definitely a lot more research to be done in this area.

Learning about the social interactions of vampire bats could gain growing significance as new research indicates that vampire bats could soon be swarming the United States, as climate change intensifies.