What Animal Has the Biggest Penis?

Typically, penises help male animals reproduce sexually with females. But, the genitalia of some creatures are downright wild.

For instance, the hermaphrodite leopard slug has two penises that are massive compared to its body size. They’re also vibrant blue and impossible to miss. That makes mating competitive. Penile spines may help remove rival sperm.

Blue Whale

Blue Whales are the largest mammals on Earth, and they also have some of the world’s biggest penises. These sea creatures’ genitalia can be up to eight times their body length!

This giant creature has the longest penis of any animal. In fact, it is the only vertebrate with a penis longer than its body. A male blue whale’s penis can reach 42.5 cm, which is more than a human’s!

The Argentine Lake Duck is another mammal that has an impressive penis. This bird’s penis can be up to 17 inches long, which is nearly as long as a human’s. Birds typically hide their penises inside their cloacae, so they are not visible to females.

Some snakes and lizards have two penises, which are called hemipenes. These are useful in mating competitions, as they allow males to mate with females from both sides of their bodies.


One of the most impressive animals in the animal kingdom is the elephant. Its penis can be up to six feet long and weighs a couple hundred pounds. This phallic weapon is used for mating and sperm delivery.

Interestingly, the elephant’s closest living relative is the rock hyrax, which looks a bit like a rodent. The reason behind the size of an elephant’s penis is a simple one: it has to be stiff enough to enter a genital opening.

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Mammals have solved this problem by putting a stiff bone called the baculum in their penises. The baculum helps maintain a strong penis, even as the penis grows longer and wider.

The elephant’s penis is also remarkable in that it doesn’t disappear after a copulation. This feature is not uncommon among mammals: it’s found in antelope, camels, deer, giraffes, and horses. This is because females have a special opening, the cloaca, that accommodates both hemipenes.


The Ron Jeremy of the animal kingdom, this crustacean sticks to rocks, shells and whales and, as a result, has the longest penis relative to body length of any creature. In fact, its penis can be up to eight times its body length.

Barnacles are hermaphrodites and mate with other similar crustaceans. They also use their long appendage to ejaculate and spread sperm around, which helps them reach distant females and spawn more offspring.

Researchers found that the length and girth of a barnacle’s penis actually varies depending on where it lives. Those in rough intertidal waters have shorter, stouter penises to help them control them in the turbulent flow, while those in calmer areas grow longer, thinner penises so they can mate more easily. Interestingly, a spined sea slug called Chromodoris Reticulata has a single-use penis that’s three centimeters long and can only be used once during its life.

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Alligators are the largest reptiles and have penises that grow proportionally to their body size. It is thought that they evolved large penises for mating purposes as it would allow them to fertilize females over a greater distance.

Their dark skin is also armored with small bony scales called scutes that act as natural armour. When their mouth is closed, only four of their many teeth are visible giving them the devilish grin they’re famous for.

While elephants and odd hoofed mammals have massive penises, they don’t come close to the length of the alligator’s erection. They can extend their phallus to up to eight times their body length. Interestingly, they have the ability to control the length of their penis and bend it during mating. This is the only known animal to have this ability. It is believed that they use their penises to help them grapple with prey and to assist with the insemination of eggs.


While slugs may get a bad rap for being cold, slimy, and eating your kale, they have one of the thickest penises in nature. They also have a unique way of having sex. When a male slug couples with a female, it drops its penis. Scientists believe the penis then regenerates, like a lizard’s tail after being cut off.

Researchers discovered this unusual behavior in the Chromodoris reticulata sea slug. This hermaphrodite mollusk has a single-use, three-centimeter-long penis that extends only during copulation. After sex, the slug discards its spined phallus into the ocean’s depths. It then grows a new one, and the hermaphrodite can be ready for another round of mating the next day.

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This slug-specific version of apophallation could be an evolutionary arms race to maximize surface area for hormone transfer, or it could simply be a practical solution. Hermaphrodites may find themselves competing for the same mates, and this slug strategy allows them to give their penises away without cheating.

Bed Bug

Bed bugs are renowned for their violent stabbing sex, and their penises are a key part of the action. They have a specialized bone called a baculum that helps them keep an erection during copulation. This helps them inject their sperm into the female’s body, and it also explains why they can spend up to 70 hours mating!

They have a pretty big advantage over mammals, which don’t have bacules. The baculum helps them remain stiff enough to pass through an orifice, and it also allows them to store sperm in bags attached to their genitals.

While many of these penises are pretty weird, Willingham says that a microscopic cave insect has the strangest penis of all. It’s a stinging, eyeless organ that penetrates and vacuums up sperm to fertilize the female. It’s basically a little penis that is willing to die for sex.

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