Sex can be painful because the males and females have different aims

Banana slugs can mate with themselves and porcupines wee to woo

Creature was voted to have the strangest sex in a Society of Biology poll

Humans may have their quirks and kinks, but sex in the animal kingdom can be truly strange and excruciatingly painful.

From banana slugs that can mate with themselves, to fish that turn their ‘boyfriends’ into a clingy parasite until only his testes are left, experts have rounded up the most bizarre and disgusting mating rituals.

And after much deliberation, scientists and members of the public have crowned the Argonaut octopus' taste in sex, whose detachable penis ‘swims’ off to mate, the weirdest in the natural world.

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Humans may have their quirks and kinks, but sex in the animal kingdom can be truly strange and excruciatingly painful. The Argonaut octopus' (pictured) mating ritual has been voted the strangest. Its detachable penis ‘swims’ off to mate with a female

A MIND OF ITS OWN

The eight-armed marine creature has a long, detachable penis in order to mate with females that are five times bigger than itself.

When a female swims by, the male Argonaut sends his penis off to swim to the female and mate with her.

In fact, the penis is a ball of sperm in a tentacle called a hectocotylus and females can be fertilised by more than one, by storing them in the mantle cavity.

The male dies soon after his unique ordeal, whereas the female can mate several times and even store multiple hectocotyli in a special cavity until they’re needed.

The bodies of male Angler fish actually fuses to the female's, turning it into a parasite. A female is shown

In the past, scientists that caught female specimens confused the attached penises for parasitic worms.

The male mollusc won almost a third of votes in a survey set up by the Society of Biology to identify the strangest animal sex.

People who participated in the survey on Facebook and at the Green Man Festival, among other events, voted the Angler fish the second kinkiest creature.

GONE FISHING

Female Angler fish have the unique advantage of a built-in fishing rod and males use their teeth to hitch a permanent ride on a female in a bid to get an easy meal.

But in some species, the male's body actually fuses to the female's, turning it into a parasite - and the ultimate clingy boyfriend.

Eventually, the male is absorbed into the female until all that is left is a pair of testes, ready and waiting for when the female needs her eggs fertilised.

This is a conveniently evolved method of reproduction for the deep sea, when encounters between the sexes can be very rare.

SEX CHANGE

Green spoon worms take the idea step further.

They start life sexless and while females grow to become three and six inches (8cm to 15cm) long some larvae become attached to their body and become male, measuring just a couple of millimetres long.

The males are inhaled by the female and live trapped inside her body, where they constantly eject sperm.

BITTEN OFF MORE THAN IT CAN CHEW?

Banana slugs copulate in a variety of unusual ways because they are hermaphrodites.

They have the reproductive organs of both the sexes, can act as both male and female at the same time, and on rare occasions, will even mate with themselves.

Their Latin name, dolichophallus, means ‘giant penis’ and the slugs do indeed have enormous genitals that are almost as long as their bodies.

Male banana slugs must choose their mate carefully as if the female is too small, their penis might get stuck.

Unable to pull out afterwards, the only option left is to bite off the other slug’s reproductive organ.

Banana slugs (shown mating) have the reproductive organs of both the sexes, can act as both male and female at the same time, and on rare occasions, will even mate with themselves

50 SHADES OF PREY: WHY DO ANIMALS HAVE PAINFUL SEX David Urry, Regional Coordinator at the Society of Biology explained that ‘sexual conflict’ occurs when the two sexes have different ideal outcomes from reproduction, normally in the mode and frequency of mating. Examples include males losing their penises and females being stabbed by them. So, males may benefit from multiple matings, while multiple mating may harm or endanger females. ‘What can result is an evolutionary arms race between the sexes, each trying to gain the upper hand,’ he told MailOnline. It’s not known how painful such sex is to animals, but rough play is common. For example, cats have barbed penises which scrape the inside of a female’s vagina, leading come people to note that female cats cry out in pain during the act. In an article for The Huffington Post, Hal Herzog, Professor of Psychology at Western Carolina University, questioned whether animals may enjoy painful sex, which he likened to acts of sadomasochism. Seeking expert advice, he said bear researcher Bob Jordan said bears show ritualised displays of dominance and submission during sex, and Gordon Burghardt of the University of Tennessee said sexual play is also seen in some spider species. ‘But while these examples bear superficial similarities to human S & M, they don't strike me as really being the same phenomenon as Ana experiences in Fifty Shades,’ he wrote. Advertisement

NOSE SEX PLEASE

Not voted quite as disgusting is the Hooded seal.

Males inflate their their uniquely elastic nasal cavities into what looks like a pink balloon, which is deemed attractive by females.

The strange act communicates health and superior status to both other males and females they are attempting to attract and the creatures shake the membrane to make seductive noises, which vary depending on whether the seal is under water or on land.

WET'N'WILD

The ‘least weird’ mating ritual according to the poll, with only three per cent of the vote, is displayed by the porcupine, but it involves the male drenching the female in urine from seven feet (two metres) away.

If it turns her on and she is impressed with his pheromones, then they will mate, and she won’t let him stop until he’s physically exhausted.

When that happens, the insatiable female finds another prickly partner with a full bladder.

Perhaps unsurprisingly, porcupine sex is very rare as females are only receptive to sexual advances for between eight and 12 hours per year.

You may imagine that porcupine sex would be a prickly affair due to their sharp spines, but in fact, both animals relax their spines to avoid injury.

Unlike some painful animal sex, the male doesn’t grip the female in any way and thrusts by flexing and strengthening his knees.

MIOW-CH!

Many animals, such as the domestic cat, have spines on their penis, which rake the walls of the female’s vagina, to discourage her from finding another mate straight away.

And it can get a lot rougher than that.

For example, male bed bugs stab their penis through the female’s abdomen so they can inject sperm straight into her bloodstream.

When a male honeybee mates with a queen his testicles can explode and penis break off so he dies and some female lizards bear sex scars for weeks.

Ducks are known to be rough lovers and the Argentine duck has the longest penis of any bird species at around 17 inches (43cm) long.

Male Hooded seals inflate their their nasal cavities into what looks like a pink balloon (pictured), which is deemed attractive by females. 'The inflated inner nose of a hooded seal may seem disgusting to us but it is potentially the most attractive and glorious thing a female hooded seal has ever laid eyes upon,' said Mr Urry

The ‘least weird’ mating ritual according to the poll, with only 3 per cent of the vote, is displayed by the porcupine, but it involves the male drenching the female in urine from seven feet (2 metres) away. A mother and baby are pictured

It’s shaped like a corkscrew and because the birds are promiscuous, they use it to ‘lasso’ females, who try to escape from it.

Short-beaked Echidnas have a four-headed penis, with two heads working at any one time so they are guaranteed to perform.

But the insurance policy comes at a price, because their testes swell to 200 times their normal size, and because they are located inside the animal's body, it is thought to be very uncomfortable.

Little is known about how painful such sex is for animals, but it may seem strange from an evolutionary point of view if the sex hurts.

It’s easy to imagine how animals may be put off the experience if it is too rough, perhaps putting future generations at risk if they shy away from sex.

MAKE LOVE NOT WAR

But David Urry, Regional Coordinator at the Society of Biology explained that ‘sexual conflict’ occurs when the two sexes have different ideal outcomes from reproduction, normally in the mode and frequency of mating.

So, males may benefit from multiple matings, while multiple mating may harm or endanger females.

‘What can result is an evolutionary arms race between the sexes, each trying to gain the upper hand,’ he told MailOnline.

Some animals have incredibly rough sex, which can end in death. Male bed bugs (a microscopic image is shown) stab their penis through the female’s abdomen so they can inject sperm straight into her bloodstream

THE ARGONAUT OCTOPUS The Argonaught octopus technically has eight arms, but also has a long, detachable penis in order to mate with females that are five times as large. Fully grown temales are arounf eight inches long, while males can be just one inch. They are also some 600 times lighetr than females. When a female swims by, the male Argonaut sends his penis off to swim to the female and mate with her. In fact, the penis is a ball of sperm in a tentacle called a hectocotylus is inserted into the female's pallial cavity. There's it's locked in so it's stored in her cavity. In this way, females can be fertilised by more than one male by storing their 'penises' in her cavity. The male dies soon after his unique ordeal, but the females move one and find new mates. Advertisement

‘Occasionally, in extreme instances, this can result in what is known as traumatic insemination.

‘The best example of this is from bed bugs Cimex lectularius, where males initiate mating by climbing onto the female and piercing her abdomen with their spiky penis. The result can cause significant damage to the female, and occasionally death.

‘It is believed that the male bed bug adopts this strategy to ensure paternity as the female cannot risk intercourse with other partners as it is far too physically damaging.

‘It is important however, that this evolutionary arms race does not sway too far in favour of one sex as it may threaten the persistence of the species as a whole - if male bed bugs killed all the females via traumatic insemination then no eggs would be laid at all and everyone loses.’

ODDS ONES OUT

He pointed out that humans have only been around for 40,000 years so our idea of what constitutes sex is very recent when compared to the estimated first instance of sexual reproduction, which dates back in the fossil record to 1.2 billion years ago and was seen in single celled organisms.

‘Humans as a result, are relative newcomers to the sex scene,’ he said.

‘With humans, sex and pleasure go hand in hand, and this is closely linked to the phenomenon of the orgasm.

‘It certainly seems to make sense, in that sex is essential for our persistence and so we should want to do it, which is why it has evolved to be so much fun.

‘In the grand scale of things however, the orgasm has emerged fairly recently, appearing around 65 million years ago, with the advent of mammals.’

NOT TONIGHT, LOVE...

Despite the fact that sex is believed to be pleasurable among mammals, most species do not partake in sexual activity throughout the year and Mr Urry says there are good reasons for this.

‘Wolves for example, abstain for most of the year, as in the wild having sex makes one vulnerable to attack.

Despite the fact that sex is believed to be pleasurable among mammals, most species do not partake in sexual activity throughout the year. For example, wolves (pictured) abstain for most of the year because males are vulnerable when they are 'locked' inside females for over half an hour

‘For example, a male wolf gets "locked" inside the female for up to half an hour.’

Family planning is also important as pups would likely not survive the harsh winter where food is scarce.

‘Mating rituals therefore, and more specifically the timing of their initiation, are important in giving a clear signal that now is a good time to get it on.’

However, because the animal kingdom is so diverse, he said that it’s hard to make generalisations when it comes to mating rituals.

‘There are many thousands of ways of going about what in essence is a very simple thing: the coming together of a male and female individual and subsequent fusing of male and female gametes,’ Mr Urry said.

‘This diversity is a wonder to observe, but can also give evolutionary biologists a headache and there are many mating behaviours which are still unexplained.

‘What is important to remember however, is that the mere fact that they exist for us to observe, means that whatever quirky way a species has evolved to go about the act of courtship and mating, it works.