Hawkmoths, seen here pollinating an angel’s trumpet flower, are one of several animals with interesting uses for their genitals. Photograph by Mark W Moffett, National Geographic.
Genitals are useful for transferring sperm, but why stop there? Some animals have evolved unusual and creative ways to use their naughty bits to trick predators or attract mates.
Recently, scientists discovered that hawkmoths have an unusual defense against bat sonar—by rubbing their genitals together, the moths produce ultrasonic sounds of their own. These sounds jam the bat’s sonar and give the moths a chance to escape.
Hawkmoths aren’t the only animals that use their genitals in unexpected ways. Read on for more examples of creatures that have found creative uses for their nether regions.
Flatworm Penis Fencing
Marine flatworms (Pseudobiceros hancockanus) are hermaphrodites, having both male and female genitalia. When they mate, they have to determine who will become the mom and who will become the dad. And since creating eggs takes more energy than creating sperm, both partners would prefer to use their male parts to impregnate the other.
They decide who gets to be the daddy with a clash of their penises. The flatworms parry with their dagger-like genitalia, attempting to stab their partner in order to inseminate it. The first to succeed becomes the male of the pair, delivering its sperm into the other.
Bedbug Hypodermic Penis
Bedbugs reproduce through the appropriately named technique of “traumatic insemination.” The male uses his hypodermic-like penis to stab through the female’s exoskeleton and pierce her abdomen. He injects his sperm directly into her body through the wound. The sperm diffuses through her body and eventually finds its way to her ovaries, where it fertilizes her eggs.
As you might expect, this can be an ugly experience for the females. The wounds are susceptible to infection and can be detrimental to the females’ health and longevity. Fortunately, female bedbugs have evolved a special abdominal organ known as the spermalege where the males stab them, which appears to reduce some of the damage from traumatic insemination.
Detachable Spider Penis
For the orb-weaver spider (Nephilengys malabarensis), sexual cannibalism—where the female eats her partner—is fairly common. So mating is risky business. But male orb weavers have a trick to avoid being eaten by the females: They use reproductive organs called palps to transfer their sperm to their mate. If she looks at him a little too hungrily while they’re mating, he can detach his palp and run off to live another day.
This strategy may actually help his reproductive success. The male spider’s palp continues to transfer sperm into the female long after the rest of him has gone. It also blocks the female’s genitals, barring her from mating with other males. (Related: “Why Sea Slugs Dispose of Their Own Penises.”)
The male paper nautilus, or argonaut octopus, also has a detachable trick up its sleeve. Males possess a specialized, extended tentacle, called a hectocotylus, where they store packets of sperm.
When a male paper nautilus detects a female, the hectocotylus can break free from his body and swim over to her under its own power. The hectocotylus inserts its load into the female’s mantle and can remain active, depositing sperm in her even as its owner goes on his merry way.
The first scientists to observe the hectocotylus in action actually misidentified it as a parasitic worm attached to the female paper nautilus.
The water boatman (Micronecta scholtzi) is a tiny freshwater insect that shows that size doesn’t matter.
The 0.07-inch (2-millimeter) bug produces the loudest sound of any animal relative to its body size. How does it do it? By rubbing an appendage on its abdomen against its penis. Scientists recorded chirps from the water boatman at an ear-splitting 99 decibels. That’s about as loud as a power mower.
Like most ostentatious displays, the purpose of the water boatman’s singing is to attract a mate. For females, it’s not the size of the boatman, it’s the motion of its singing penis.