Leopard Slug Mating is Well....Strangely Beautiful

or "Ewwww, I Can't Look Away"

So once in a while I have to veer off track and bring you something completely different (much like my previous post on 50 foot cockroaches). Today I want to share with you something so gross and disgusting that it's almost beautiful (sort of like hairless cats and Shar pei dogs), leopard slug mating. Now for those of you that are gardeners you probably find leopard slugs (Limax maxiumus) a great nuisance that eats your vegetables and leaves slimy trails everywhere, but they are really much more complex (and a good cup of stale beer put out at night will take care of the problem).

Slugs 101

All slugs and snails are in the phylum Mollusca, along with squid, clams, and octopi. Slugs are gastropods, literally meaning "foot mouth". Leopard slugs have a noticeable mantle on their backs and in almost all species it's black spotted. They also have two optic tentacles with eye spots on the tips and two below them for feeding and tasting. Their anal opening is under the mantle (on the right side of the head) and they are hermaphrodites with both male and female genitalia.

Also on their mantle is a large hole or respiratory opening (called the pneumostome) that leads to lung-like tissue for respiration. Their respiratory opening opens and closes at regular intervals to prevent dehydration. Slugs glide along on a large muscular foot. The leading edge of the foot is called the "skirt."  Mucus is produced in glands on the "sole" of the foot. This mucus has specific pheromones that attract other slugs and also acts as a signal, trail marker, and travel lubricant. Underneath the smallest pair of tentacles is the rasping and chewing mouth part that are used to chew plants and vegetation.

Leopard Slugs

Limax maximus (literally meaning "great slug") is an accidental introduction from Europe. Leopard slugs can be quite large, up to eight inches! They don't have a visible shell, because like their cousins the cuttlefish their shell is internal as a form of structural support. It's found under the mantle.

There are a variety of patterns to Limax but most have a greyish brown body with spotting.  Leopard slugs are generalists and feed on a variety of plant matter, fungus, compost, young seedlings, and rotting vegetation. They have also been known to eat other slugs. Limax maximus are nocturnal, feeding only at night. They prefer dark and damp places because they need to remain moist for respiration and to prevent dehydration.

Slug Boogy

Now, on to the really fascinating part about Limax maximus. Leopard slugs are unique among slugs because they have a very distinctive mating ritual. It all starts in the spring. At night, when two fertile slugs cross slime paths they begin to circle and court, following each other around, nibbling each other and touching with antennae (all very sensual). It's a very slow slimy waltz that can last for hours. Eventually some unknown signal sends them up into the trees (whispering sweet nothings?). They climb out onto a branch, twine into each others slimy embrace and create a bungee cord of thick stretchy mucus which they lower themselves down on. Swinging in the air like squishy acrobats they wriggle and writhe until their white semi-translucent penises evert from the gonadopores (or genital opening) on the right side of their head (yes, always the right).

These penises expand into a frilly furl of translucent membranes, then entwine in a knot-like pattern as the slugs spin and twirl while hovering over the ground. The knot gradually changes shape to a flower-like structure and then eventually re-knots. Sperm is exchanged in the last phases of "flowering" and then the penises withdraw back into the sides of their heads.

As if hanging from a mucus thread, spinning and everting a penis from the side of your head wasn't enough, then the slugs chew the mucus bungee-cord and drop to the ground. But wait! What happens if the penises get stuck? Yes, it can happen. After hours of hanging around with everted penises, these can become structurally so entwined that they can't be separated. This is when the leopard slugs may resort to apophallation, or chewing off of the penises (after which the slug drops to the ground and crawls on his..wait her...merry way). Now this sounds worse than it really is. You're thinking, "Man, what a rough way to go, he could never mate again." But, remember that leopard slugs are hermaphrodites. If they do indeed end up chewing off their penis then all they have to do is revert be being a "female" and continue mating as only one sex next time without giving sperm to another slug.

Now do I have you curious enough to want to watch the video?

Wouldn't this make some sort of great B-flick movie, like "Night of the Mating Leopard Slugs?"