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Bat uses huge heart-shaped penis to maneuver female in unusual mating act

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Bat uses huge heart-shaped penis to maneuver female in unusual mating act

In one of the strangest animal behavior discoveries this year, male serotine bats living in a church attic in the Netherlands have been captured on camera engaging in marathon sessions of non-penetrative sex – the first-ever instance of superficial-contact mating among mammals.

However, the devil is in the details. Researchers from the University of Lausanne soon discovered that this very unusual mammalian behavior was a far more complex strategy, because the male serotine bat (Eptesicus serotinus) also happens to sport a penis that, when erect, measures a fifth of the length of his 2.75-inch (7-cm) body and seven times longer than his partner’s vagina.

“By chance, we had observed that these bats have disproportionately long penises, and we were always wondering, ‘How does that work?’” said first author Nicolas Fasel. “We thought maybe it’s like in the dog, where the penis engorges after penetration so that they are locked together, or alternatively maybe they just couldn’t put it inside, but that type of copulation hasn’t been reported in mammals until now.”

(A) Ventral and (B) dorsal views of the erect penis. (C) Scaled digital microscopic photographs of E. serotinus female genital tract: (A) a formalin-fixed and (B) a HE-stained histology slide of a female genital tract. c = cervix, ov = ovary, r = rectum, ub = urinary bladder, ut = uterine horn, v = vagina. The female died on the 14th of May 2015 and was not pregnant. The scale in the lower right corner accounts for both images. [1] Length of the erect penis shaft (16.4 mm). [2] Width of the erect penis terminal swelling (7.5 mm). [3] Outer diameter of the cervix (0.7 mm) and [4] vagina (1.1 mm). (D) Copulation of an Eptesicus serotinus pair. The male, above on the drawing, uses its erect penis to pass by the uropatagium of the female, below on the drawing. The terminal swelling of the erect penis is firmly pressed against the vulva, without vaginal intromission. (E) Numbers of copulations merged by month. (F) Average number of bats captured at underground site per night. The numbers of capture events between 2001 and 2022 occurring during the respective months are indicated in brackets.

While in nature, species that are paired up for mating typically ‘fit’ together to ensure the best chance of reproductive success – of passing genes onto offspring, and therefore completing the key biological driver of most life. The fact that this tiny Eurasian bat was not only sporting a large phallus, but one that had a pronounced heart-shaped tip seven times wider than a female’s vaginal opening, was a giant puzzle for scientists.

However, this puzzle was solved 97 times over, when the animals were filmed mating. Yes, 97 times. As the researchers also happily report, one event lasted 12.7 hours, while the average copulation spanned 53 minutes.

“We are trying to develop a bat porn box, which will be like an aquarium with cameras everywhere,” joked Fasel.

While the researchers did not witness ejaculation, they report that “abundant seminal fluid was found around the vulva and lower abdomen” of the female bats.

However, because of the footage and handy position of the cameras in the church roof and also a Ukrainian wildlife center (which captured four of the 97 events), the researchers were able to witness something truly remarkable in the mammal world. Instead of penetrative sex, the male used his ill-fitting appendage like a third arm, pushing the female bat’s tail aside to engage in contact mating, resembling the ‘cloaca kissing’ common in the bird world.

NSFW: The bat's not-so-secret weapon at rest
NSFW: The bat’s not-so-secret weapon at rest

While a highly unusual scene in the animal kingdom, it’s unlikely this mating mechanism has come about by chance. In fact, scientists believe this penis ‘arm’ has evolved to overpower the female tail membranes, which the bats could use to avoid sex.

“Bats use their tail membranes for flying and to capture the insects, and female bats also use them to cover their lower parts and protect themselves from males, but the males can then use these big penises to overcome the tail membrane and reach the vulva,” said Fasel

This sort of copulation strategy ‘arms race’ is common in nature.

The researchers now hope to look at bat mating behavior on a broader scale, to see if this technique is unique among E. serotinus or it spans species. In what may come as a surprise in the wake of this comprehensive study, little is known about bat sexual behaviors.

The research was published in the journal Current Biology.

Source: University of Lausanne (French), Scimex (English)



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