Clitor-hiss: scientists find the snake clitoris for the first time

In a world first, Australian scientists have anatomically described the clitoris in female snakes.

A new study, published in Proceedings of the Royal Society B: Biological Sciences, fills in an important gap in our understanding of female genitalia across the animal kingdom – a part of the anatomy which is often overlooked in scientific research, despite the overwhelming focus on their male counterparts.

Scientists now know that the snake clitoris – called a hemiclitoris (Pl: hemiclitores) – does in fact exist, which opens up exciting new questions about the dynamics of sexual reproduction in snakes, such as whether snakes mate through coercion, as has been previously assumed, or whether it’s a matter of seduction, like in other animals such as humans.

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Snake clitorises have been overlooked for too long

Dr Jenna Crowe-Riddell, a Postdoctoral Researcher in Neuroecology at La Trobe University in Melbourne,  says that before herpetologists only knew the hemiclitoris is present during development.

“In embryology, it’s the same bundle of cells that turn into a hemipenis(Pl: hemipenes)  or it will regress, in response to sex hormones, and form the hemiclitoris.”

Diving deeper into the mentions of hemiclitores in research papers, the team found that scientists were misidentifying them – often confusing them with the prominent scent glands in the tail of the female.

On the other hand, papers have described a structure that looked like hemipenes, but in a snake with ovaries (and sometimes functional ovaries).

“So, they’re looking at intersex individuals, which is quite common in the animal kingdom.

“But once we knew what the clitoris actually looked like, we could say: ‘No, I think what you found is far more similar to a hemipenis.”

Delving a little deeper into the hemiclitoris

The discovery was driven by University of Adelaide PhD student Megan Folwell, who Crowe-Riddell says is fascinated with snakes – especially female reproductive anatomy – and was doing dissections for her thesis.

“She came across what she thought was a clitoris and she brought it to us and was like: ‘What do you think?’ And I was like: ‘I’ve never thought about that!’”

Folwell went on to dissect nine different species of snake and looked more closely at the tissues of the Australian common death adder (Acanthophis antarcticus). Using histological analysis she determined its cellular structure – identifying red blood cells, vascular spaces, and nerve bundles consistent with erectile tissues and are hallmarks of the clitoris. And their presence suggests it may swell and become stimulated during mating.

The team also looked at the hemiclitores using micro-CT scanning.

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“Then we could make a 3D model to really figure out where it’s sitting in the tail, how it’s different from hemipenes, how it is similar, and how it’s different from the scent glands which are butting up right against them,” explains Crowe-Riddell.

They found that, unlike hemipenes, the hemiclitoris structure doesn’t include sulcus spermaticus (which transports sperm), spines, or retractor muscles.

This means they’re non-reversible.

“In lizards and snakes, the hemipenes sit inside the tail and while in there it’s kind of like when you ball up your socks,” says Crowe-Riddell.

“Then, the male will inflate one of the hemipenes and it will evert out of the cloaca so that it can be inserted during mating. Once mating is done there are special muscles that retract that hemipenis back in to become that ‘backwards sock’ again.”

Hemiclitores cannot be everted, they’re internal structures. Crowe-Riddell says this may explain why they’ve been overlooked for so long: ”…hemipenes are much more in-your-face.”

“Herpetologists will often embalm and fix the animal with the hemipenes everted, because they can give you a lot of information.”

Illuminating the other side to serpent reproductive anatomy

Now that they know what the female genital anatomy looks like, Crowe-Riddell says herpetologists should be looking at hemiclitores across all species of snake to investigate whether its structural diversity mirrors hemipene diversity.

“Hemipenes have fascinated herpetologists for hundreds of years, they’re incredibly diverse structures – just like lots of genitals are, actually, because they evolve so quickly across animals,” she says.

“So, we’ll just apply the same questions to the hemiclitores: What do they look like? Are they variable? Does that correspond with the male genitalia?”

Illuminating this other side to serpent reproductive anatomy also raises questions about previous assumptions about mating behaviour.

“I think if all we had before was the hemipene, it’s very easy to generate hypotheses related to coercion in mating. So, the male pursuing females, pestering them into mating, and once they’re mating causing a lot of damage with the spines on their hemipene.

“But now we’ve got a whole other side of the story that we’ve been missing. And for me, I think that opens up questions around seduction. That’s how it’s used for mammals that have clitorises, so why not snakes?”