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WHY SUCH A LONG PENIS?
30/11/2023

Yes – I thought that would catch your attention … but I am writing about bats, the serotine to be exact, Eptesicus serotinus (Schreber, 1774). This is one of the earliest bats to emerge in the evening (sero means late in the day in Latin) and larger than many of our bat species: it has a wingspan of about 37cm. Favouring woodland, serotines hunt around the edges of vegetation and can be observed circling individual trees/treetops as well as catching insect prey around street lights. In England, they have a mainly southerly distribution, mostly south/south-east of a line from Norfolk to the Severn Estuary. For those with bat detectors, the echolocation calls are described as “up to 23ms-long frequency-modulated calls with an almost constant-frequency end part at 23-27kHz”.
The extraordinary feature of this bat’s anatomy is that the male’s penis is as much as 22% of its whole body length when erect – that is seven times longer than the female’s vagina! Understandably, scientists obviously wondered why and decided to find out. Work by Professor Nicolas Fasel of the University of Lausanne in Switzerland has shed light on it. After nearly a hundred video recordings of mating, they observed that these bats do not have penetrative sex, something which is very unusual indeed in mammals. It seems the females have a membrane covering their vulva and the males use their penis rather like an arm to move this out of the way and, the researchers believe, deposit sperm just at the vaginal entrance, the coupled pair remaining in an embrace sometimes for over twelve hours.
Further research is needed on exactly what happens in detail in fertilization in this reproductive process and how this has evolved, but it makes a fascinating discovery to report. For more, please see this reference: Current Biology DOI: 10.1016/j.cub.2023.09.054.
Betts Ecology carry out a lot of work surveying bats and their habitats, and providing/protecting roosts and foraging territory. We think we know much about them but this is something new and there is certainly a lot more to discover!
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