Top 10 Strangest Genitals in the Animal Kingdom

This post is probably not work or school (or mind) friendly.

It comes in all shapes and sizes, and a nearly unimaginable array of colours and accoutrements. But I’m not talking about Nicki Minaj’s hair, I’m talking about something far more interesting – the private parts of animals. In honour of Valentine’s Day, here are 10 of the strangest genitals in the animal kingdom:

1. Ducks

Most birds don’t have penises, so the ones that do need to compensate for the rest. The Argentine Blue-bill pulls more than its fair share of the weight. The small duck species has the longest penis, proportionate to body size, of any vertebrate (check #7 for the overall winner for animals). The Blue-bill’s penis has clocked in at up to 42.5cm – about the same length of its body. In its relaxed state, it lies coiled up inside the body – like a snake (more on them later), ready to strike. When erect, it explodes from the body in a cork-screw. In a beautiful piece of symmetry, the vagina of a female duck is also cork-screw shaped, but in the opposite direction.

He seems surprised.

He seems surprised.

Ah, Nature.

2. Snails

Detachable penises are not uncommon in the animal kingdom (see #8), but nobody does it quite like snails. Snails are hermaphrodites (each individual having both lady-parts and man-parts), and when two snails come together, they complete a lengthy and complicated ritual prior to mating (think of it as snail-flirting). Part of this ritual includes trying to stab each-other with calcified darts stored in an internal sac (okay, think of it as the 50 Shades of Grey version of snail-flirting).

Love darts come in a variety of shapes and sizes. Credit: Nat Geo

Love darts come in a variety of shapes and sizes. Credit: Nat Geo

For a long time, scientists thought the darting served a ‘stimulating’ function (for more weird stimulation, see #6). But it turns out to be more important than that. The female part of snails collects and stores the sperm of multiple suitors in internal sacs,  which it then uses when it decides to reproduce. But in order for sperm to make it safely into the storage sacs, it must negotiate the internal anatomy of the snail, including a part of the body called the bursa copulatrix, which digests sperm. More than 99.98% of sperm is digested before reaching the relative safety of the storage sacs. The darts mitigate this digestion.

Each dart is covered in mucus which triggers a hormonal shut-down of the bursa copulatrix, allowing more of the male’s sperm to be stored in the female, and increasing his reproductive success relative to any other individuals the snail has mated with. Like Cupid’s arrows, hitting a snail with a love dart increases the odds that she’ll have your babies – if Cupid’s arrows were mucus-covered harpoons.

They don't have very good aim. 1/3 love darts miss the mark. In this case, one excited individual stabbed his amour in the head. Oops.

They don’t have very good aim. 1/3 love darts miss the mark. In this case, one excited individual stabbed his amour in the head. Oops.

3. Spider monkeys

A trip to the Calgary Zoo is never complete without visiting the spider monkeys (where I usually plead with them to explain their behaviour to me, so I can finish my thesis). My favourite part is when parents, trying to be helpful, point to the monkeys with dangly appendages and say, “Look, that one’s a boy!”

No, it’s not.

"It's a bird! It's plane! It's...kind of strange"

“It’s a bird! It’s plane! It’s…kind of strange”

Spider monkey females have enlarged clitorises, to the point where, to the untrained observer, they appear to be flaccid penises.   Nobody is entirely sure why. It may be to help females and males identify each other at distance in the forest (it definitely helps primatologists), or it may give off hormonal clues to specify when females are ready to mate. Or it may be an evolutionary prank to confuse zoo visitors.

4. Snakes

You know what they say, two heads are better than one. Snakes (and many lizards) have a hemipene – essentially a two-headed penis. This is held inside the body for most of the year, but can be squeezed out in an erect state when needed for mating. Imagine squeezing toothpaste out of the tube – but instead of toothpaste, you get a two-headed spiny snake penis. Now go brush your teeth.

The stuff of nightmares.

The stuff of nightmares.

5. Whales

Attenborough explains it better than me:

6. Cats

Cats are kinky. When cats mate (usually after a prolonged argument), the end of the process is signalled by the female yowling loudly as the male withdraws. She isn’t mad because he’s refusing to cuddle, she’s in pain – because the penis of a male cat is tipped with backwards facing spikes. As the male exits the female, this spikes rake the inside of her vaginal canal.


But, the thing is, they’re kind of into it – that raking is needed to trigger ovulation. Without the penis spikes, the female wouldn’t release an egg, and cats wouldn’t reproduce. It also has the handy effect of scraping out any other sperm lodged in the female cat from previous mating. Gross.

7. Barnacles

When it comes to finding love, barnacles have it rough. Cemented to the rocks, they’re like a home-owner stuck in a long mortgage: they can’t choose their neighbours, and they can’t change them. But (and I don’t recommend you try this with your neighbours), barnacles can mate with them from a long, long way away. Barnacles have probably the longest penis in the animal kingdom, proportionate to their body size. The penis of a barnacle can be up to 40 times the length of its own body, making it able to reach over and touch its neighbours, without needing to leave the comfort of home.

barnacle penis

8. Argonauts

An argonaut.

An argonaut.

Argonauts are a genus of octopus, also called the ‘paper nautilus’, known for the thin shell the females secrete which helps them control buoyancy. The males have their own special adaptation too, but it’s a little more disturbing. Male octopi and squid develop a sperm-transmission organ called a hectocotylus. They’re sort of like the arm equivalent of testicles – male squid and octopi store sperm packets on the tips of these arms. When they find an enticing female, they present the hectocotylus, and hope the female will accept their gooey present.

The hectocotylus of a normal octopus.

The hectocotyli of a normal octopus.

But the argonaut has developed a more direct route. The argonauts hectocotylus develops as a pouch underneath its eye. When the argonaut reaches sexual maturity, and a female is in the area, the pouch explodes, and the hectocotylus emerges: a free-swimming, mobile, sperm-filled missile. It swims until it finds a female, and then attaches to her skin, where it remains until she decides to use it to fertilize eggs.

Detachable argonaut junk

The male, by the way, dies immediately – understandable, given the traumatic experience of having a detachable, free-swimming penis explode out of your cheek.

9. Bats

You know when a man does something incredibly stupid in pursuit of a woman, and everyone assumes he’s just “thinking with the wrong head”? That’s the case all day, every day, for bats. The bigger the bat testicles, the smaller the bat brain, and vice versa. Brains and balls are both energetically expensive to develop and maintain, so bats really do have to make a choice as to which one they will think with. The one they choose depends on the mating system of the species. More promiscuous species have larger testicles. Large testicles produce more sperm, which increases the chances that your sperm, rather than a competitors, will fertilize a female. But that comes at the cost of a smaller brain.

A confederacy of dunces (judging by the testicle size).

A confederacy of dunces (judging by the testicle size).

The biggest bat balls account for up to 10% of the bats bodyweight. For a 180 lb man, this would be the equivalent of lugging two 9 lb bowling balls around in your pants every day – and then being dumb to boot.

10. Insects, of all shapes and sizes

Insects have terrifying penises. They look like medieval weapons. Pictures are better than words.

A weevil.

A weevil.

A beetle.

A beetle.

Honourable Mentions:

The echidna’s four-headed penis.

The female hyena’s enlarged clitoris

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