Beavers have no external genitalia

Everything comes out from one hole.

We know beavers for their mad engineering skills in building dams. But my mind was blown when I recently discovered that they have no external genitalia. How does everyone not know about this? It’s an awesome fact that I believe should be broadcasted to the whole world.

Beavers weirdly have no external genitalia. Photo by Amaya Alvis on Unsplash

So, what do they have instead? Well, they have one hole - a cloaca.

The cloaca serves as a all-in-one opening. It’s where they shit, reproduce, scent-mark and pee. But they do have internal reproductive organs - testes in males and ovaries in females.

So, with both males and females having one cloaca, how do you tell them apart?

It’s honestly not that simple. You can’t just tell by looking at their cloaca alone, as for both sexes, it looks exactly the same. You can’t even look at their physical characteristics since both males and females are about the same weight and size. In some cases, the females are larger than the males. The only time you can physically tell them apart, is when a female has teats from having a litter of kits.

It’s super hard to tell female and male beavers apart simply by looking at them. Photo by sempre dilunedi on Unsplash

But there’s one reliable method of sex determination that works. And it’s an interesting one.

Whether it’s to monitor a population or to research beaver colony dynamics, scientists will occasionally have to go out and trap beavers (and release them of course!). Once they have captured a beaver, the researcher will pop the beaver in a dark bag while leaving the beaver’s cloaca exposed. The dark bag helps calm the beaver while the researchers work their magic.

The researchers will palpate the beaver’s abdomen to look for a particular gland - the beaver’s anal gland. The anal gland is a small gland that produces liquid used for scent marking and communication.

Once they’ve found it, they’ll palpate the beaver’s abdomen, so that the anal gland actually pops out of the cloaca. Then they gently milk the gland until a liquid substance squirts out.

Beavers will squirt out a liquid substance if their anal glands are massaged properly. Photo by Eduardo Goody on Unsplash

If the liquid substance is brownish and smells like motor oil, it’s a male beaver. Whereas if it’s whiteish and smells like bad cheese, it’s a female.

There is another method researchers can use for sex determination. And that’s by feeling if the beaver has a penis bone, known as a baculum (fun fact, humans are one of the few mammals that don’t have a baculum). Females for obvious reasons, don’t have a baculum.

So, you essentially have to massage and sniff a beaver’s butt to determine its sex. Or try and feel for its penis bone. I guess that’s one way of doing a gender reveal.

What’s even weirder, is that their anal secretions can also be used as food flavourings. Something which I stumbled across while researching this topic. I think I’ll leave that topic for my next post.