Birds do it, bees do it,
Even sentimental fleas do it!
Let's do it, let's fall in love
- Cole Porter

The birds and the bees have long been used as examples of natural sex, the assumption being that things proceed along the lines of 'boy bee meets girl bee, soon there are baby bees'. All those other things to do with sex such as Kama Sutra positions, gender ambiguity and top-shelf porn are for humans only, aren't they?

You may be surprised to find that animal sex is every bit as raunchy, exciting and, above all, amusing as anything that humans can come up with! Read on for the unexpurgated details.

Let's Start With Penises

We human males are very fond of our penises. We worry about how big they are and form a huge pharmaceutical industry just to make them bigger, from powdered rhino horn and Spanish fly to modern drugs promoted by spam. But human males are not particularly outstanding in that department compared to some other animals.

What a Whopper!

The biggest penis in the world belongs to the blue whale, coming in somewhere around ten feet long. The whale keeps it tucked inside when he's not using it so that it doesn't get in the way. Whale penises are muscular things which can bend and hunt around for an opening.

Other types of whale also have large penises. Whalers hunting sperm whales in the 18th and 19th Centuries would use the skin of the whale's penis as a one-piece wrap-around waterproof apron.

OK, so the blue whale is the biggest animal in the world, and you'd expect a large animal to be correspondingly well endowed. But even some tiny creatures have relatively large penises. The common barnacle, a tiny crustacean which lives in a shell stuck to rocks or the bottoms of ships, has the longest penis in relation to the size of its body of any creature, being up to ten times the height of the barnacle itself when extended. If a man were similarly endowed, his penis would be about 50 to 60 feet long. With this enormous reproductive tool, the male barnacle can seek out and fertilise suitable females without ever shifting from his rock: the ultimate couch potato!

Strange Construction

Not all penises are constructed in the same way. Badgers have a reinforcing bone in theirs. Cats have barbs on the end, which cut the female and encourage her to ovulate. Pigs have a penis shaped like a corkscrew. The corresponding cervix is similarly twisted.

Always Carry a Spare

As if one wasn't enough, some animals carry a spare in case the first is exhausted. Snakes and some lizards have two penises. Since female snakes are hard, dry creatures devoid of lubrication, the male snake has a different strategy to mammals when it comes to erections. Instead of the penis growing large and then him trying to fit it into the female, he keeps it inside-out then inflates so that it unrolls straight into the female opening, like blowing up a long narrow balloon.

They Were a Happy Couple Until She Broke it off

Cephalopods (that group of molluscs which includes squids, octopuses, cuttlefish and nautiluses) must win the prize for unusual penises.

The octopus has eight arms which it uses for walking and for grabbing things. In the males, one particular arm, usually the third one on the right, also serves as a penis, transferring sperm from the male to the female. Octopuses mate only once in their lifetime - after mating, the male octopus becomes lethargic, stops eating and soon dies. So he doesn't need the penis again. Many species have developed the ability to break off the third arm and leave it inside the female. This makes successful reproduction more likely.

The male paper nautilus goes one step further. When the male detects a receptive female, he avoids intimacy. It's sex at a distance. His spermatophore-bearing tentacle detaches itself from the body and swims - under its own power - to the female, being in effect a swimming penis. Just how this peculiar arrangement evolved is anyone's guess. Perhaps it has something to do with the fact that the female paper nautilus still retains a molluscan shell, while the male has lost his armour and looks more like an aspiring octopus. Without a shelly defense, the male may not want to get too close to the female!

Let's not Forget the Vagina

Female dogs and wolves have an unusual strategy for holding on to a mate. They have enormous muscles in their vagina which clamp onto the male's appendage during mating. These canines can stay locked together for up to 30 minutes after mating. This appears to be so that the sperm of the mate that the female has chosen have a chance to fertilise her eggs; if the female became available for mating with another male immediately, this latter's sperm might replace the sperm of the first mate. It also gives her a chance to wring every last drop out of the experience.

The female usually ignores the dog attached at the other end, going about the normal business of life such as sleeping or walking with him hanging precariously off her tail end.

Showing You're Interested

Of course before getting down to the business of sex, animals have to have some way of showing they're interested in each other. Many mammals rely on the female giving off perfumes called pheromones when she's ready for sex, and the males just come and get it. But in some species, much more elaborate mechanisms are necessary. Birds tend to do mating dances, with all sorts of neck twining, foot waving and calling.

Some types of monkey show they're interested by flashing their eyebrows at each other. Such monkeys have brightly coloured eyelids, so an eyebrow flash is an unmistakable sign.

Snails, on the other hand, make use of 'love daggers' - they produce these small sharp darts inside their body, and when they start to entwine with another snail, they thrust the love dagger into the other snail's body, signalling they are ready for sex. Since snails are hermaphrodite, each snail being both male and female, the happy couple often exchange daggers, each one stabbing the other one. The pain from the dagger makes the snail more receptive to sex when it happens.

Slugs, which are also hermaphrodites, will sometimes bite off their partner's penis, to force the partner to take the female role in the mating. This practice is known as 'apophallation'.

Who Does it With Whom

In most mammal species, humans included, the normal course of affairs involves sex between males and females, with regular changes of partner. Monogamy is rare in the mammal world. Birds, on the other hand are much more monogamous - many bird couples will stay together for life. If there is an imbalance between the number of males and females, there will be many of one sex left over, forcing these into homosexual relationships. Such relationships are common in the bird world. Black swans in Australia have been known to form male-male pairs, who will then steal eggs from females and raise them as their own. Penguins also form male-male couples, while among seagulls, lesbianism is common.

Homosexuality isn't confined to birds, though. The dolphin is one mammal that has a thriving gay community. Male dolphins practise anal intercourse, and even fellatio using their blowholes.

In species where it isn't necessary to have one-on-one mating, massive orgies may become common. One species that does this is the frog - frog orgies are huge affairs with hundreds of frogs participating in free-for-all sex.

Enjoying the Sensation

The main reason for sex is the reproduction of the species - those who do it survive through their offspring; those who don't are quickly forgotten about. But such high-minded ideals are not enough to lure animals into this self-exposing activity - so sex has to be fun. All animals seem to enjoy it. But some can get a kick in quite an unusual way. Stags' antlers, for example, when they are still covered in the fur known as 'velvet', are highly erogenous zones. Stags have been seen to acquire enormous erections after rubbing their antlers in long grass for just a few seconds.

Duck Rape

Most male birds do not have any equivalent of a penis. Sex between consenting birds involves lining up two holes, one in the male and one in the female, so they really do have to be consenting. It is for this reason that the world of birds has evolved such elaborate courtship rituals, much more so than any other type of animal; because the sexual act requires the co-operation of both parties.

Of course there's always an exception. Male ducks, known as drakes, have enormous sexual organs. These are known as phalluses rather than penises, and can be as long as the drake. This enables a drake to enjoy sex without the co-operation of the female. Rape is common in the duck world. Often a group of drakes will gang-rape a duck, sometimes even resulting in drowning the poor creature.

Female ducks have evolved to counter the threat of undesired insemination by having correspondingly long and complex genital passages, known in birds as the lower oviduct. The duck's oviduct is not just a straight tube but has side passages as well. The female duck can store the sperm in a side chamber, and later eject it if she isn't satisfied. So although as many as one in three of duck matings are rapes, in nine out of ten of these, the offending sperm is ejected, so 97% of all duck offspring are the result of the choice of the mother.

Ultimate Sex

The ultimate sex involves the fusing of two souls together to make one. This happens in the unlikely guise of the angler fish, one of the ugliest animals around (by our standards, anyway). These monsters live extremely deep in the ocean, where it is permanently dark. They have a glowing lure on the end of their nose, which they use to attract other fish that come to see what the dancing light is. The angler fish then gulps them down with its enormous jaws. Scientists studying the angler fish were puzzled that every one ever caught was female. Where were all the male angler fish?

It turns out that the male angler fish is very small. He has a great problem finding a female in the dark because, like many predators, these animals are few and far between. So when he finally finds a female, he literally holds on to her for life. He bites hard, and pierces her skin. He then attaches himself permanently to the female, linking his blood supply directly into hers, getting all his nourishment from her for the rest of his life. His contribution is that he provides sperm anytime there are any eggs that need to be fertilised. So the tiny leech-like parasite that the scientists found on the female angler fish was really a male, engaged in the ultimate act of sex.

Sex as a Life or Death Struggle

Sex is a serious business in the world of insects and spiders. The male may be literally taking his life into his hands to have a bit of sex. The female will frequently kill the male just after or even during mating. The female praying mantis regularly bites off the male's head during sex (which doesn't stop him finishing the act), and the black widow spider is notorious for eating the male after sex. In both cases, the male gets to propagate his genes while the female gets a nourishing meal to help her raise the babies. In the case of bees, the queen bee may pull the sperm-transferring member out of the male and store it inside her for safe-keeping, so that she doesn't need to mate again for a long time. The male dies from disembowelment.

Sex as a Means of Saying Hello

The complete opposite to this life-or-death struggle must be the casual sex practised by certain apes. We're not talking about the human species, but a close relative, the bonobo, a type of chimpanzee. Bonobos have perfected the art of casual sex. There's nothing like a little intercourse for breaking the ice. Bonobos do it on every possible opportunity, without any restrictions on gender, age or even family ties. It's the normal bonobo way of saying hello.

It's more interesting than a peck on the cheek, anyway.