12 Animal Sex Facts You Might Not Know

From an Alligator's Permanent Erection to a Snail's 'Love Darts'

If you like to tune in to TMZ to catch up on the latest celebrity sex scandals, imagine what you're missing by not watching Discovery or National Geographic instead. The details of animal mating can be titillating, amusing, and just plain weird, all at the same time.

Here are 12 unusual animal sex facts, ranging from the permanent erections of alligators to the arrow-shaped "love darts" wielded by snails and slugs:

Male Alligators Have Permanent Erections


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Penises vary widely across the animal kingdom, but a universal theme is that this organ changes size or shape before or during the act of mating, then reverts to its "usual" configuration. That's not so for alligators. The males are endowed with permanently erect penises, layered with numerous coats of the stiff protein collagen, that lurk inside their cloacas (chambers that contain digestive and reproductive organs), then burst out suddenly like the baby alien from John Hurt's stomach in "Alien." The six-inch-long penis of an alligator isn't everted, or turned outward, by muscles, but by the application of pressure on its abdominal cavity, clearly an essential bit of reptilian foreplay.

Female Kangaroos Have Three Vaginas

Kasngaroo with joey laying down

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Female kangaroos (all marsupials, for that matter) possess three vaginal tubes but only one vaginal opening, eliminating any confusion on the part of their mates. When males inseminate females, their sperm travels up either (or both) of the side tubes, and about 30 days later the tiny joey travels down the central tube, from which it slowly makes its way to its mother's pouch for the remainder of its gestation.

Antechinus Males Copulate Themselves to Death

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The antechinus, a tiny, mouselike marsupial of Australia, would be almost anonymous except for one odd fact: During their brief mating season, the males of this genus copulate with females for up to 12 hours straight, stripping their bodies of vital proteins in the process and dismantling their immune systems. Shortly afterward, the exhausted males drop dead, and the females go on to bear litters with mixed paternity (different babies have different fathers). The moms live a bit longer to nurture their young, but they usually die within the year, having had the opportunity to breed only once.

Flatworms Fence With Their Sex Organs

Flatworms fencing
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Flatworms are among the simplest invertebrate animals on earth, lacking well-defined circulatory and respiratory organs and eating and pooping via the same body opening. But all bets are off during mating season: The hermaphroditic critters, which possess male and female sex organs, sprout pairs of dagger-like appendages and fence in slow motion until a "hit" is scored, straight into the other's skin. The "loser" is impregnated with sperm and becomes the mother, while the "father" often goes on dueling until it becomes a mother itself, further complicating the confused gender roles.

Male Porcupines Urinate on Females Before Sex


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Once a year, male porcupines cluster around available females, fighting, biting, and scratching one another for the right to mate. The winner then climbs onto a tree branch and urinates copiously on the female, which stimulates her to go into estrus. The rest is somewhat anticlimactic: The female folds back her quills so as not to impale her partner, and more routine insemination takes only a few seconds.

Barnacles Have Enormous Penises


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You might imagine that an animal that spends its entire life tethered to one spot has a relatively sedate sex life. In fact, though, barnacles (one shouldn't say "male" barnacles since these animals are hermaphroditic) are equipped with the largest penises, relative to their size, of any creatures on earth, as much as eight times longer than their bodies. Essentially, frisky barnacles unfurl their organs and attempt to fertilize every other barnacle in their immediate vicinity, at the same time, presumably, being probed and prodded themselves.

Mating Snails Stab Each Other With 'Love Darts'

A snail dart
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Some hermaphroditic species of snails and slugs wield the invertebrate equivalent of Cupid's arrows—sharp, narrow projectiles made of calcium or hard proteins—as a preliminary to the act of mating. One of these "love darts" pokes into the receiving snail's skin, sometimes penetrating its internal organs, and introduces a chemical causing it to be more receptive to the attacking snail's sperm. These darts don't introduce sperm into the "female's" body; that happens the old-fashioned way, during the act of copulation.

Female Chickens Can Eject Unwanted Sperm

Rooster and hen

 Paula Sierra / Getty Images

Female chickens, or hens, tend to be smaller than roosters and often can't resist less-than-desirable males insistent on mating. After the act, though, enraged or disappointed females can eject up to 80% of the offending male's sperm, allowing for the possibility that they might then be impregnated by roosters higher up in the pecking order.

Male Honeybees Lose Their Penises While Mating

Bees mating

Rene Nortje / EyeEm / Getty Images

Everyone talks about colony collapse disorder, which is devastating bee populations worldwide, but not many people seem to care about the peculiar plight of the individual drone honeybee. Before a queen bee can assume her exalted title, she begins her life as a virgin bee and must be inseminated by a male to step up to the throne. That's where the unfortunate drone comes in: In the course of mating with the heir apparent, the male's penis rips off, still inserted into the female, and he flies off to die. Given the gruesome fate of male honeybees, it's no surprise that full-grown queens deliberately breed them for use in their "mating yards."

Sheep Have a High Rate of Homosexuality

Sheep Mating

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Homosexuality is an inherited biological trait in some members of the animal kingdom, and nowhere is homosexuality more rife than among male sheep. By some estimates, almost 10 percent of rams prefer to mate with other rams rather than females. Lest you think this is the unintended result of human husbandry, studies have shown that the behavior of these sheep is reflected in a specific area of their brains, the hypothalamus, and is a hard-wired rather than learned behavior.

Male Anglerfish Merge With Females During Mating

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Anglerfish, which lure their prey with fleshy structures growing from their heads, live in the deep ocean and are relatively scarce, producing a limited supply of available females. But nature finds a way: The males of some anglerfish species are orders of magnitude smaller than the opposite sex and literally attach themselves to, or "parasitize," their mates, feeding them a constant supply of sperm. It's believed that this evolutionary trade-off allows the females to grow to "normal" sizes and thus prosper in the food chain. What happens to males who don't find receptive females? They die, sadly, and become fish food.

Male Damselflies Can Remove the Sperm of Competitors

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Most animals that lose out during mating season must be content with their fate. Not so with the male damselfly, which can use its weirdly shaped insectile penis to literally scrape the sperm of its immediate predecessor out of the female's cloaca, thus increasing the odds of propagating his own DNA. One byproduct of this strategy is that it takes damselflies an unusually long time to complete the act of mating, which is why these insects can often be seen flying in tandem over long distances.

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Strauss, Bob. "12 Animal Sex Facts You Might Not Know." ThoughtCo, Aug. 28, 2020, thoughtco.com/animal-sex-facts-you-didnt-know-4118876. Strauss, Bob. (2020, August 28). 12 Animal Sex Facts You Might Not Know. Retrieved from https://www.thoughtco.com/animal-sex-facts-you-didnt-know-4118876 Strauss, Bob. "12 Animal Sex Facts You Might Not Know." ThoughtCo. https://www.thoughtco.com/animal-sex-facts-you-didnt-know-4118876 (accessed June 4, 2023).