It’s something they didn’t tell you at school and you never see on TV wildlife shows. The story of homosexuality in animals is one of the best-kept secrets of the natural world.

If you have heard the occasional reports of gay penguins being discovered in a zoo – most famously Wendell and Cass in New York – you may have assumed these were rare cases.

But the experts now agree bisexual behavior exists in virtually all species (1,500 studied so far and counting) from the humble fruit fly to chimpanzees – our closest relatives.

Dogs, donkeys, crickets, cockroaches, rabbits, raccoons, mice, moths, hamsters, horses, octopuses and orangutans. They are all at it.

Many animals have an exclusively same-sex phase at some point in their lives – though they won’t always stay ‘gay’ forever. Others are completely bisexual.

And there are plenty of obvious reasons.

A lot of species have a harem system and junior males, filled with testosterone, turn to each other while the dominant male controls the females. And sometimes it’s the ruling female stopping her competitors from mating.

There are also times when it seems like it might be a mistake – frogs in the mating season often attempt to have sex with the first stranger they see.

Others just seem to enjoy it or use sex to make friends and reduce conflict.

The truth about animal sexuality is far more fascinating and complicated than you may have realized.

As GSN celebrates our Gay Pet Month, read our run down to hear amazing tales of group sex, penis fencing, animal prostitutes – and some committed same-sex couples raising young.

Dolphins

‘Dolphins are gay sharks’ goes the old joke but there’s actually something to it.

Male bottlenose dolphins pair off with other males during their youth but never do so with females. And the females use their beaks to stimulate another female’s genitals, while swimming.

Amazon dolphins get into groups of three to five – mostly of males but sometimes with one or two females and use their snouts and flippers for group sex as well as rubbing their genitals together.

Giraffes

Bruce Bagemihl highlighted mating giraffes in his 1999 book which really lifted the lid on the scientific secret of same-sex behavior in animals.

Surprisingly nine out of 10 matings are between males – but scientists were overlooking them.

Bagemihl says: ‘Every male that sniffed a female was reported as sex, while anal intercourse with orgasm between males was only “revolving around” dominance, competition or greetings.’

Deer

It’s not just about gay animals – even gender identity isn’t all it seems in the animal kingdom. Male red deer, in particular, often cross the gender divide by looking like females.

During the rutting season when the stags fight for access to the harem of does, some stags which look like does can sneakily impregnate the females without being challenged by other males.

Sheep

Around one in 10 male sheep engages in homosexual sex. Some perform anal sex and others achieve orgasm by rubbing their penis around another male’s tail.

And it appears to be ‘hard-wired’ ¬– in 2003 scientists produced research showing there is a difference in the brain anatomy between ‘gay’ and ‘straight’ rams.

Simon Levay, a neuroscientist famous for his work on sexuality, says that rams are rare as they can be exclusively homosexual whereas most animals are more bisexual or only have same-sex activity at some points in their lives.

Griffon vultures

Two male griffon vultures Dashik and Yehuda at Jerusalem Zoo came to public attention in the 90s when they built a nest together.

Kind keepers gave them an artificial egg to care for and later replaced it with a newly hatched chick. They became great parents, bringing their little one water from a pond, feeding him and stopping him falling from the nest.

It didn’t last forever though – like many animals who show same-sex behavior, a few years later they both ended up nesting with females.

Flatworms

Some species of flatworm are hermaphrodites – producing both eggs and sperm.

In these cases, they engage in penis fencing. They will ‘fence’ with their two-headed, pointed, dagger-like penises. It’s so fierce that sometimes, one of the fencers’ swords gets broken.

In the end, the winner gets to impregnate the other with the sperm being absorbed through the skin.

Watch it all happen in this NatGeo clip here:

Seahorses

The idea that seahorses mate for life is a myth – in fact they are flirty, flighty, fairly unfussy and pretty much bisexual. A 2007 study looked at three species and found only one, the British spiny seahorse, had ‘faithful’ members but they were in the minority.

The scientists also found that 37% of their sexual encounters were with the same sex. Big-bellied seahorses of both genders were found to be bisexual and not to prefer an opposite gender partner over a same-gender one.

Lizards

Some lizards are able to breed without sex – their embryos don’t need to be fertilized to develop. (Other reptiles like geckos, boa constrictors and the mighty Komodo dragon can do this too.)

But that doesn’t mean these cold-blooded animals don’t get hot under the collar.

Female whiptale lizards have sex with each other to stimulate egg production. The ones who are going to ovulate take the ‘female role’ – but when their hormone levels drop again, they swap over and take the ‘male role’ in sex. In this way, like a lesbian commune, they can almost do without men altogether.

Lions

Lionesses are often seen to have sex with each other in captivity but this behavior is not so well recorded in the wild – could it be an example of institutional homosexuality?

But the kings of the jungle do form pair-bonds with each other and will spend a few days regularly caressing, nuzzling and mounting each other. About 8% of male lion mountings are with other males.

Bed bugs

Even if you’re not getting much action in the bedroom, there’s a good chance any bed bugs you have are having a whale of a time.

The males will take a shine to any other bed bug which has just fed and, when they mount other males this can result in injury due to their needle-like penis being shoved into their abdomens. Because of this, it seems attraction is unwelcome by the males who are mounted though – they produce pheromones to put their randy comrades off.

Elephants

With male and female elephants tending to live apart, it’s not surprising that a large amount of the sex they have is homosexual.

But elephant society also means that while heterosexual encounters are relatively fleeting, the bonds between males, living in twos or threes away from the female herd, are long lasting.

And despite their enormous size, elephants appear to be sensitive lovers, enjoying kissing, trunk intertwining and placing their trunks in each others mouths before mounting each other.

Penguins

When scientists discovered homosexuality among polar penguins 100 years ago, it was so shocking the report was translated into Greek to avoid it becoming more widely known.

But since then the media has been friendlier and some zoo penguin gay couples have become global stars – like New Yorkers Wendell and Cass and later Silo and Roy.

While penguins form committed pairs, their sex lives are much more varied than you might have been told. Females are not beyond sleeping with strange males to get the pebbles they need for their nests – a rare example of animal prostitution (which is also seen in chimps who will have sex in return for food).

Bonobo chimpanzees

All the great apes (the family of animals which includes us) have homosexual sex. But the bonobo chimpanzee – our closest relative – is the most bisexual of all.

A massive 60% of bonobo sex is between two females. Scientists now believe these chimpanzees use sex to reduce conflict. Both male and females will rub each other sexually to reduce tension or to re-establish their bonds after a disagreement.

They literally make love, not war – maybe that’s something we could learn from.

The science bit

Some scientists point out that you can’t really describe animals as ‘gay’, ‘bisexual’, ‘homosexual’ etc.

Certainly same-sex or opposite-sex activity in animals doesn’t come with the baggage often associated with it in human society and animal sexuality is not fully understood.

But an alternative lexicon isn’t really available so we’ve used the words most humans will understand. After all, same-sex activity in the animal world has been a secret for far too long and disguising it in non-communicative language doesn’t advance science. So pedants, please consider this our disclaimer.

GSN’s Gay Pet Month (this October) is about celebrating all animals, great and small (though possibly not bisexual bed bugs) – particularly the ones we have in our homes. If you’ve got a cute or interesting pet, find out how it could be a prize-winner here. And the animal or owner’s sexuality doesn’t matter. Gay Pet Month is supported by Direct Line pet insurance to encourage more people to protect their cats and dogs.