There are many things that fascinate us about the animal kingdom, from certain species’ habitats and their genetic makeups to their habits and overall dispositions. But one of the things we can’t help but continue to be the most fascinated by is the mating rituals of certain creatures and critters… especially when they happen to have some of the strangest genitals on the planet, like these animals below.

Harvest mice

Scientists theorize that rodents tend to have longer penises because female rodents are quite promiscuous, so sexual competition is fierce. But by far it’s the harvest mouse that clocks in with the biggest member of the bunch.

“Everything’s relative, of course,” evolutionary biologist Steve Ramm said following a study published in American Naturalist on the subject. “So although big for its body size, the penis bone in R. megalotis is still only seven to eight millimeters long. I don’t think the phrase ‘hung like a harvest mouse’ will be catching on any time soon.”

Turtles

Despite their “old man” stigma, these sea creatures are, as one writer puts it, “horrifically well endowed.” Seriously, they’re pretty huge. When erect, a male turtle’s penis can grow nearly 50 per cent in length, 75 per cent in width and 10 per cent in depth. Considering some species of turtles have shafts that can be nearly half their body size to begin with, that is some pretty formidable growth.

Echidna

These creatures, which along with the platypus are the last remaining monotremes on Earth, are anything but monotonous in the genital area. That’s because the male enchidna has a penis with four heads. Yup, four-headed penises are a real thing. The science is still out on why they’re built this way, but one theory is that because the female has two canals, the penis works like a double-barreled shotgun that fires two heads on one side and two on the other to best increase their chances of procreating. Science, huh?

Sharks

These (sometimes) predatory animals have a dual advantage when it comes to mating, since they happen to have two penises, or claspers, as their dongs are dubbed. It’s unclear why they have two, since they only use one at a time, but whatever the scientific advantage there’s no denying they’re pretty impressive to look at.

Bean weevil

We feel sorry for the female seed beetle (or bean weevil), because the penises features on the males are the stuff of horror movies. These organs are complimented with sharp, hard spikes that absolutely inflict injuries during mating. The theory is that the injuries stop the females from mating again, ensuring the fertilized eggs are the ones to survive.

Blue whales

Although there’s nothing particularly strange about the blue whale penis other than the fact that the genital slit is hidden during daily activity, it is the largest sized penis on the planet and that makes it worth mentioning. Blue whale penises can be anywhere from eight-to-10 feet long, and can weigh anywhere from 390 to 990 pounds. Yowza.

Water boatman

The pen is mightier than the sword, and this tiny water bug’s penis is louder than the rumblings of an African elephant. Or at least it is comparative to size. The water boatman’s penis actually “sings” when it rubs up against the ridged portion of its abdomen, creating an underwater sound that would be the equivalent of standing 15 meters away from a hurtling freight train.

Female hyenas

Not only do female hyenas run the show when it comes to mating, but they also tend to be more muscular and larger than their male counterparts. And, thanks to the presence of a hormone called androgen, they also have a clitoris that holds their birth canal, and protrudes about seven inches from their bodies. Obviously, that makes her pretty well endowed.

Sea slugs

We’re fascinated by one particular species of sea slug found in Indo-Pacific waters, the chromodoris reticulata. These hermaphrodites feature the world’s only known example of a disposable penis, which snaps off every time it’s finished mating. Yet somehow, it’s ready to go again the next day. How, you ask? Apparently the penis is roughly three centimeters long, but only a centimeter of that is exposed at a time. Bulking up the chances of procreating? These creatures happen to have three such penises coiled up inside of them.

Barnacles

If barnacles seem boring, that’s probably because you’ve never taken the time to get to know them intimately. Not only do these hermaphrodites have penises that can be up to eight times the length of their bodies (the longest relative to its body size of any animal), but the genitals evolve to suit its environment. As in, animals living in rougher waters will develop stouter penises to withstand strong waves, while those living in gentle waters may develop longer penises designed for maximum reach. Talk about going with the flow.

Alligators

There’s much to fear about these creatures, but it seems like we should add penis to that list. We could get into it in our own words, but we feel the genitals are best described in this National Geographic article:

“Here are the highlights: it’s permanently erect; it shoots out like toothpaste from a tube; and it bounces back because it basically has a rubber band attached to it.”

Indeed.