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Sperm + egg = baby. Simple eh? Well, not always. As Adam and Hannah discover in The Curious Cases of Rutherford and Fry, there are lots of creatures doing things differently...

1. Did you drop something? Only my penis...

A species of sea slug can perform a nifty trick. Found in the Pacific Ocean, the Chromodoris reticulata discards its penis every time it finishes mating. Luckily for the slug, this isn’t game over. The full organ is much longer and is coiled up inside the slug’s body. It uses this to replenish the missing part.

2. Dragons and virgins

Ganas the Komodo dragon lives in London Zoo and is a “parthenogen”. This means he’s the result of a virgin birth. His mother spontaneously fertilised her own eggs and so Ganas doesn’t have a father.

A few creatures are able to perform this spectacular feat, including snakes, insects and sharks. But in Komodo dragons this method of reproduction can only produce male offspring. So a female living alone could give birth to a son by parthenogenesis, have sex with him and repopulate the area with dragons.

3. Stab in the dark

Nudibranchs, otherwise known as sea slugs, are hermaphrodites, meaning they have both male and female parts. One type, called Siphopteron species 1, which lives off the coast of Australia, has a very unusual method of foreplay. During their romantic entwine, as their bodies wrap around each other, they try to stab each other in the head with their penises. The successful stabber delivers neurochemicals directly into its partner’s brain. These “appeasement substances” put their partner off having sex with anyone else.

4. Bite me!

Elsewhere in the animal kingdom, females are definitely on top. And if you’re a redback spider, sex is a treacherous sport because females like to indulge in a spot of post-coital cannibalism. The most a brave male can hope for is to have sex perhaps twice during its lifetime.

Amazingly, being eaten after sex is a successful evolutionary strategy because when the female spider has had a good meal, she’s less likely to look for another sexual partner for tea.

5. Spicy mushrooms

Fungi have the greatest number of sexes in the natural world. One group, the Basidiomycetes, which includes mushrooms and toadstools, has hundreds of different sexes, or “mating types” as they are known. Their polyamorous ways mean that they can maximise the number of potential sexual partners available for reproduction. Very useful when you’re a mushroom and you don’t get out much.

6. Curious clones

Some creatures have managed to do away with sex completely. Bdelloid rotifers – tiny worm-like creatures just half a millimetre long – are all female and reproduce by cloning themselves.

Most asexual creatures don’t survive for very long, because their lack of genetic diversity means they are easily wiped out by diseases and parasites. However, these rotifers have evolved a clever trick: they can dehydrate themselves, meaning they can outlive many parasites which need water to survive.

7. Sperm-stealing salamanders

All-female groups of blue-spotted salamander, found in the Great Lakes of North America, have managed to do away with men by stealing sperm from other species.

In the Spring, the passions of frisky salamanders begin to surge. Mole salamanders swim into the water to find a mate. The males perform a sexy dance to impress potential partners. Next they drop a spermatophore, a small jelly pyramid containing sperm, and female mole salamanders dive down to capture them with their vents. However, rival female blue-spotted salamanders swim in and steal these packets before the female mole salamanders have a chance to claim them.

The blue-spotted salamanders throw away the genetic material and just use the machinery of the sperm to stimulate their own eggs to fertilise, producing more daughters to carry on their sperm-stealing tradition, known as kleptogenesis.