Nature documentaries often show the animal kingdom to be a weird and wonderful place, but animal genitalia don’t usually get the attention they rightfully deserve. To right this wrong here’s a list of five of the most bizarre bits on offer out there.

Let’s start our titillating exploration of the icky world of animal sex in the exotic Down Under, with nothing less than Oz’s national animal: the Kangaroo. Females have three vaginas. The left and right vaginas carry sperm to the two uteri at the top, whilst the middle vagina delivers the jellybean-sized joey from one of the uteri to the mother’s pouch. This arrangement also allows the female kangaroo to be perpetually pregnant: whilst one joey is developing inside her pouch, another embryo can be held in stasis, waiting for its sibling to grow up and move out.

Vaginas, naturally, require penises to perform their reproductive function. And although some might reassuringly claim that size doesn’t matter, it’s clear that some species have missed the memo. If you’re smiling, though thinking of the sperm whale when envisioning the biggest penis out there, wipe that smile off your face. It is in fact the banal beach barnacle that has the biggest willy (relative to body size) of the animal kingdom. Somewhere between eight and 40 times the length of their body.

Of course you don’t strictly have to be male to sport a penis; take hyenas for example. Being aggressive is useful within the hyena community and the feistier the mother is, the more androgen, a male sex hormone linked to aggression, she passes to her young. Female hyenas with a lot of androgen develop clitorises that can be up to 7 inches long, so lengthy it’s often mistaken for a penis. During birth the clitoris becomes the birth canal for a cub to squeeze its way through. Yikes.

Speaking of willies, male ducks have one that’s long and anticlockwise spiralling. When it’s flaccid it’s tightly coiled, but as soon as it enters a vagina it becomes erect within a third of a second with ejaculation happening just as quickly. Males often force themselves upon females and reports of duck gang rape are quite common so female ducks have evolved vaginas that trick the males. Their vaginas are filled with trick openings so if she doesn’t want to have sex she can direct the male to ejaculate in a dead-end but when she does, she can relax internal muscles to make sex easier.

But most likely, the prize for weirdest penis goes to the Echidna, known also as the spiny anteater. This strange looking member of the monotremi, has an even stranger looking member consisting of one shaft with four heads. Each time it has sex, two of these heads shut down and release sperm into the female’s two-branched vagina and alternates heads the next time it copulates.

If you enjoyed these facts come and hang out with I, Science at the Science Museum Lates on Wednesday 24th February for more of the same and a game of Whose Penis is it Anyway?