"Serotinus" bats can have sex for up to 12 hours

The serotinus or Eptesicus serotinus bat is often found in forests, hedgerows, parks, fields, grasses, and even old buildings in Europe. Body length is 6-8 centimeters and weighs 15-35 grams. The feathers on the face, wings and ears are dark brown or black, but the underparts are yellow-brown.

This bat feeds on flies, moths, and beetles both while flying and picking them up on the ground and trees. They also forage near lamp lights as moths are attracted to light. This bat usually comes out in the early evening, earlier than other bat species. It mates in the fall and hibernates throughout the winter.

The size of the maleserotinus bat's penis is very large. A study conducted by biologists from the University of Lausanne, Switzerland, Nicolas Fasel and colleagues, found that these bats do have an unusually sized penis.

The serotinus bat's penis is already enlarged before it comes into contact with the female's vulva.

In fact, as written by Nature, November 20 2023, the length of his penis when erect can reach 22 percent, i.e. almost a quarter of his body length. The tip of this bat's penis is round and heart-shaped. "With a shape (penis) like that, it seems like it would be difficult for him to get in anywhere," he said.

The penis size of the male serotinus bat is disproportionate. Its length and width, when erect, reaches seven times the size of a female bat's vagina. Therefore, sexual intercourse by penetrating the penis into the vagina is impossible.

This condition makes the serotinus bat, as written by Livescience, 20 November 2023, the only mammal that has sex without penetration, also known as contact mating. This condition is different from other mammals which usually have sexual intercourse through penetration.

Evolution is different

Mammals are a group of animals that nurse their young. Species that fall under this group include bats and humans. The evolution of the penis in male mammals has allowed them to deliver their sperm close to the egg during mating. In this group, fertilization occurs inside the body and birth occurs externally.

However,serotinusbats evolved a different evolutionary strategy. Instead of inserting his penis into the female's vagina, the male bat actually uses his genitals to remove the sheath or membrane covering his partner's genitals. After that, the male will press the vulva, the outermost part of the female bat's genitals.

Also read: Humans Trigger Behavioral Changes in Some Mammals

"Initially, we thought the mating process for serotinus bats would be like that of dogs, namely that the penis would enlarge after penetration and the mating pair would lock together," said Fasel. Apparently, the serotinus bat's penis was already enlarged before it came into contact with the female's vulva.

Generally, bats use the membranes on their tails to fly and catch insects for food. In addition, female bats also use the membranes on their tails to cover their lower body and genitalia from male bats. However, with their large penis, male bats can unveil the membrane on the female bat's tail to touch her vulva.

Fasel and colleagues obtained evidence of mating without penetration from recordings of the mating process of 97 pairs ofserotinus bats in Dutch church attics and at a bat rehabilitation center in Ukraine. The study, published in the journal Current Biology, November 20 2023, did not find a single sexual act involving penetration.

Contact mating in serotinus bats is carried out by the male bat grabbing the female bat's back and biting the nape of the neck, as if they were hugging. Next, the male moves his pelvis so that his erect penis is pushed firmly against his partner's bat vulva. Although there is no penetration, this process is believed to transfer sperm from the male bat to the female.

After the vulva is found, the male then remains silent and continues to press his penis against the vulva. This mating process takes an average of 53 minutes. However, there are also pairs of serotinus bats that are capable of contact mating for 12.7 hours.

Also read: Penguin-style Sexual Monogamy

After the sexual intercourse, the fur around the female bat's stomach appeared wet, indicating the presence of sperm or semen from the male bat. However, since this study was based only on video recordings, researchers need direct samples to confirm that the male bat actually experienced ejaculation during the prolonged embrace.

However, an evolutionary biologist from the University of Vienna, Austria, Mihaela Pavličev, said the existing evidence shows that the researchers' interpretation of the mating behavior ofserotinusbats is correct.

This video recording becomes the first evidence documenting non-penetrative sexual contact or copulation in mammals. In the animal world, contact copulation is easily found among birds. During the copulation process, male and female birds will press their cloacas together.

Cloaca is a hole where the digestive waste, urinary tract, and reproductive tract are excreted. The process of cloacas rubbing against each other, also known as "cloacal kiss," is actually the process of transferring sperm from the male bird to the female bird.

Therefore, Pavličev considers the process of sexual intercourse without penetration in serotinus bats to be something special. “I don't know of any mammals that transfer sperm (during mating). "So, this study describes unique characteristics," he said.