This article was last modified on March 22, 2011.

Comparative Animal Penis Studies

Let’s face it: the penis is the most fascinating animal part in evolutionary history. Sure, the eye is also amazing, and really blows the mind when you think about how it came about. But the penis? Wow! I cannot even begin to imagine how such variety has arisen.

Even in human males, the penis is an interesting thing. The shapes vary only slightly, but the difference in size runs on such a wide scale. What other animal has such a wide range within a single species?

On this page, I would like to alphabetically cover the varieties of animal penises, traits that make them interesting or unique, and speculate on how they came about through evolution.

Argentine Lake Duck (Oxyura vittata)

Most male birds don’t have penises — they copulate by briefly touching genital openings, called a “cloacal kiss” — but the Argentine Lake Duck has a corkscrew-shaped penis 42.5cm long. Scientists speculate that the giant penis may be an example of “runaway” sexual selection, where female preference drives male anatomy to ever-greater extremes, as in the peacock’s tail. The drake’s penis has a brush-like tip, which the males probably use to scrub the sperm of previous mates from the female’s oviduct.


This specialized octopus can use its penis without having physical contact with a female. Like many cephalopods, the penis is a special tentacle called the hectocotylus. In the case of the argonaut it detaches and swims to its mate, embedding in the female and impregnating her. The males only mate once in their short lifetime, whereas the females are iteroparous, capable of having offspring many times over the course of their lives. The hectocotyl arm was first described in the biological works of Aristotle, and it was widely disbelieved until its rediscovery in the nineteenth century.


Despite spending its entire lifetime bathed in frigid seawater, the barnacle doesn’t suffer from shrinkage. On the contrary, the barnacle has a penis up to 50 times its body length — making it the world’s largest penis, relative to size. They are immobile and need the length to reach their mates.


The bedbug does not mess around with female genitals. Instead, the male uses its dagger-like penis to pierce the body of the female and inseminate her.


The male bee’s genitals literally explode and snap off inside the queen. Afterward, the males wander off to the corner and die. The evolutionary rationale is that the detached genitals act as a plug preventing other males from mating with the queen.


A chimpanzee penis has “spines” on it. A misleading term, because they are more like small bumps. Scientists think they could be an “internal courtship device”, a polite way to say a vaginal stimulant. The bumpy penis may be better for removing rival sperm from the female, scientists theorize. The gene that controls the spines also creates sensory whiskers, and variations can be found in other animals.


In traditional Chinese medicine, a deer penis is said to have important therapeutic properties. Deer penis and powdered deer penis is commonly sold in Chinese pharmacies. The deer penis is typically very large and, proponents claim, for it to retain its properties it must be extracted from the deer whilst still alive. Often it is then sliced into small pieces, typically by women and then roasted and dried in the sun and then preserved while the deer looks on. Deer penis wine can be sold at $12 a glass and often as high as $450 for a two liter bottle.


The dog’s penis has a small bone in it, as well as a bulb near the base on either side, which swells five times its normal size with blood, once the dog has his penis inside the bitch and begins thrusting in preparation to ejaculate. This bulbous section, along with the female’s vaginal muscle, ensures that the “tie” cannot be broken until all the semen is pumped from both testicles, which happens as alternative spurts from each teste. Normally, the sheath which covers the penis will slide back over the penis once the swelling is down.


The dolphin, like some other cetaceans, has a retractable penis that is also prehensile, meaning it can grab, hold and wrap around an object (think monkey tail).

Echidna (Spiny Anteater)

Male echidnas have a four-headed penis. During mating, the heads on one side “shut down” and do not grow in size; the other two are used to release semen into the female’s two-branched reproductive tract. The heads used are swapped each time the mammal copulates.


Hermaphroditic flatworms duel with their penises with the loser being pierced and becoming pregnant.


A giraffe penis is a healthy pinkish flesh color and averages some 40 inches, or 3’4″ to put it plainly.


Male gorillas are relatively huge, but have what might qualify as a micropenis: 4cm in length.

Human (Homo sapiens)

Despite variation in size between individuals, the erect human penis is especially large compared to that of other primates, measuring on average between five and six inches in length and averaging about five inches in circumference. Even the most well-endowed chimpanzee, the species that is our closest living relative, doesn’t come anywhere near this. Rather, even after correcting for overall mass and body size, their penises are about half the size of human penises in both length and circumference.

Jonah Falcon supposedly holds the record for the longest human male penis. It measures in at 13 ½ inches.

Only our species has such a distinctive mushroom-capped glans, which is connected to the shaft by a thin tissue of frenulum (the delicate tab of skin just beneath the urethra). Chimpanzees, gorillas and orangutans have a much less extravagant phallic design, more or less all shaft.


Like many marsupials, the kangaroo has a bifurcated (or forked) penis, and the scrotum and testes are in the front. This matches the dual vaginas/uteri of female marsupials.


As with other cats, the male lion’s penis has spines which point backwards. Upon withdrawal of the penis, the spines rake the walls of the female’s vagina, which may cause ovulation. A lioness may mate with more than one male when she is in heat; during a mating bout, which could last several days, the couple copulates twenty to forty times a day and are likely to forgo eating.


The pig has a penis that is shaped like a corkscrew, and worked like one, too. The male, when mounted, makes thrusting actions with the penis, which repeatedly makes semi-rotary actions. Only when the spiral glans penis of the boar becomes lodged tightly in the firm folds of the cervix does the action stop and ejaculation commence. It is clear, in fact, that the locking of the penis in the cervix acts as the essential stimulus to ejaculation in the boar. It is unclear whether the male pig employs a clockwise or a counterclockwise rotation. It may be that pigs come in both versions, as with right- and left-handed humans. The female pig’s cervix is also corkscrew-shaped.

Polar Bear

Their bacula, or penis bones, were on average nearly seven inches long. Scientists have found the higher the level of organohalogens in polar bear, the smaller testicle and baculum size and weight likely were.


Sharks come equipped with not one, but two penises. The claspers (ptorygopodia) are misleading in name, because they don’t “clasp” the female at all.


The penis of the male tapir is very long when erect (>49cm). The tapir has one of the longest penis to body size ratios of any animal. The specimen of tapir believed to have the longest penis ever observed is currently on display at the Koenigsberg Zoo.


In traditional Chinese medicine, a tiger penis is said to have important therapeutic properties. The penis of a tiger is consumed in restaurants in parts of China and southeast Asia and is commonly offered as a soup delicacy. People have been known to spend up to $5700 on a particularly rare tiger penis dish, something that needed to be ordered months in advance. A dried tiger penis is more commonly sold at around $2500 in Singapore and Taiwan. The penis can be taken in soup, ground in wine (tiger penis wine), or soaked in rice. One method of preparation, particularly in the Mekong River Delta, is to place a dried tiger penis, with testicles still attached, into a bottle of French cognac or Chinese wine and let it soak for many weeks. Then, as it matures, the preparer takes sips of the liquor every night.

Also try another article under Miscellaneous
or another one of the writings of Gavin.

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