The mystery of one of the most abnormally large penises in the animal kingdom seems to have been solved thanks to a Dutch retiree, who filmed bats in the act of sex in the attic of a church.
The serotine bat does not use its huge, strange penis for penetration, but rather as a “copulatory arm” during mating, a team of European researchers said.
It is the first time that a mammal has been documented reproducing without sexual penetration, the researchers added.
The serotine bat has a wingspan of more than 35 centimeters and is common in forests in Europe and Asia.
Nicolas Fasel, a researcher at the University of Lausanne in Switzerland, told AFP that his team had been observing the species for years and discovered that its “penis is super long when erect.”
Penis seven times longer than vaginas
Their penises are about seven times longer than the vaginas of female serotine bats, according to scientists’ measurements.
Even stranger, the head of the penis expands into a heart shape, making it seven times wider than its partners’ vaginas.
The scientists were baffled.
“There’s no way it can penetrate with this structure,” said Fasel, the first author of a new study in the journal Current Biology.
Bat Mating Mystery
Relatively little is known about how bats mate because the act is difficult to observe, and scientists didn’t see a way to solve this mystery. Until one day Fasel received a strange email.
“Penis” was the first word in the subject line of the email, followed by something in Dutch and the word “Eptesicus.” “So I thought, well, that looks like spam,” Fasel said.
However, Eptesicus serotinus is the scientific name of the serotine bat, so Fasel took the risk of opening the email and watching the videos it contained.
“Then I was really amazed because we had our answer,” he said.
The email was from Jan Jeucken, a retiree with no scientific training who lives in the village of Castenray, in the south of the Netherlands. Jeucken was interested in a population of serotine bats living in the attic of a local church, where he installed cameras.
Fasel said Jeucken’s “passion made him the best observer for understanding bats,” so the retiree was named a co-author of the study.
The researchers analyzed 93 matings in the church loft, as well as four recordings at a bat rehabilitation center in Ukraine.
By filming through a grate that the bats climbed, the researchers were able to observe them mating.
Female serotine bats have a large membrane between their tail and ankles that they can use to protect their genitals.
An additional “arm”
During mating, males grab females by the nape of the neck and use their large penises as an extra arm to encircle and remove this membrane, the researchers said.
This is followed by a long, silent embrace called “contact mating,” during which sperm is transferred, with scientists not being sure how it is produced. The only thing they could confirm is that the female’s abdomen contains remains of semen.
Although this form of reproduction, also called “cloacal kissing,” is common in birds, it has never before been observed in a mammal.
For serotine bats, the process takes time. The average session was 53 minutes, but the longest lasted almost 13 hours.
Retain sperm from multiple males
Fasel speculated that female bats might use their unusually long cervix to hold sperm from multiple males for months before choosing which male to breed with.
It’s possible that other bat species mate without penetration, Fasel said, adding that more research is needed. “We could see that there are many, many species with quite strange penises,” she said.
FEW (AFP, Cell Press, Current Biology)