A 'penis' covered in spikes and even one designed to snap off. Bug members will shock you

By Jana Madlener

Containing everything from backup phalluses to tear-away penises (well, penis equivalents), the wacky world of bug reproduction isn't what you'd expect. Nor is it for the faint of heart.

In Bug Sex, a documentary from The Nature of Things, viewers are encouraged to embrace their inner voyeur and take a closer look at the interesting ways bugs get busy.

Take the black widow spider. "Spiders' sperm transfer organs are not connected to their gonads," Catherine Scott, a postdoctoral fellow at McGill University, explains in the film. Instead, the males have leg-like appendages near their mouths called pedipalps that are modified for sperm transfer. 

Before he does the deed, a male black widow will spin a special web, deposit semen on it, and then draw the fluid into structures on the end of each pedipalp called palpal bulbs. Once the male mounts the much larger female, he uses his pedipalps like turkey basters to pump fluid into her seminal receptacles — romantic, right? 

When he's finished and pulls out the bulb, the tip often breaks off. "If he breaks it off in just the right spot, it will block the opening to the female's sperm-storage organ and prevent subsequent males from inseminating her," says Scott.

It may seem alien-like, but it's par for the course when it comes to bug sex. Here are some other insects with unusual appendages.

Size matters

The thistle tortoise beetle is equipped with an impressive member — its penis is longer than its entire body! The male's reproductive organ remains coiled inside the body until it's time to mate, but when it's showtime, he uses special muscles to provide the force needed for rapid penetration. 

The length of the penis is relatively stiff at the base but gets progressively softer toward the tip, where it needs the most flexibility to weave its way through all the twists and turns of the female's maze-like reproductive tract. The female's reproductive tract has evolved in tandem with the male's penis, becoming longer and more twisting to ensure successful pairings with only the longest penises. 

Two penises are better than one

Many earwig species have an extra penis. In these creepy crawlers, both are situated at the bottom of the abdomen. Studies suggest that certain species are also "right-handed" or "left-handed," preferring to use one penis while mating, even though each is fully functional. 

Both appendages are designed to break off when needed. If a pair of earwigs are interrupted during an intimate encounter, the male can make a quick getaway, leaving his member behind in the process. Luckily, he has a trusty backup!

Role reversal

In a tiny species of cave insect called Neotrogla curvata, sex roles are reversed: it's the female that has a penis, while the male has the equivalent of a vagina.

The female's organ is known as a gynosome, and is rigid and curved. During sex, the female penetrates the male's internal chamber and the male ejaculates inside his own body. His sperm is then passed along into her gynosome and on to her sperm storage organ.

Lethal weapon

The studded member of the male seed beetle isn't intended to elicit physical pleasure. These barbed weapons are actually designed to puncture the genital tract of their female partners.

It's a mating practice known as "traumatic insemination," and it's common in many invertebrate species, with the female usually bearing the brunt of these violent trysts.

In seed beetles, researchers have observed a link between wounds in the reproductive tract lining, the length of penis spikes and successful reproduction. During sex, the spines partially break through the female's reproductive tract, allowing ejaculate to enter her hemolymph (the equivalent of a bloodstream). The longer the spikes, the easier it is for seminal fluid to bypass the tract and enter her bloodstream. Lovely. 

Big spoon or little spoon?

Male damselflies — who make annoyingly cute heart-shaped formations with their mates when they get it on — have a specific penis trait that allows them to compete with other suitors, even after their partner has previously mated. 

First, a male must woo a female, grasping on to her using claspers on his abdomen that grip special grooves on her back. If receptive, the female then brings her reproductive opening up to meet his genitals, creating the "romantic" heart shape. 

Spoon-like structures on the end of the male's organ allow it to remove any sperm that was deposited in the female during any earlier encounters. Then, he can transfer his own sperm … and he can do all this while flying! 

Watch Bug Sex on The Nature of Things.