Wild Ideas: The mating acrobatics of a huge slug   

A few years ago, I found some tiny, gelatinous eggs under a piece of wood. I found out they were slug eggs, and that was the first time I thought about how slugs reproduce. After recently finding a pair of slugs that seemed to be courting, I decided to do more research on the topic.

Slugs are gastropods, named for their basically being a large foot with a skirt underneath it and a stomach on top. They produce slime to move along the ground, sliding along on the slippery mucous in wavelike contractions. An article in “Slate” magazine explains the slime-making process:

“The slug creates its slime by secreting a mixture of proteins and sugars through its foot and combining it with water. The stuff turns into something that manages to be a liquid while the slug is moving and stiffens like drying rubber cement when the slug stands still.”

Apparently, MIT is interested in finding out how they do this. The thick slime also deters predators.

The pair of slugs I saw courting were huge — at least four inches long. Each had lines of dashes on the top and sides of its foot and leopard-like spots on its shield (or mantle), which comes between the foot and the head. The marking pattern, particularly the spots, varied between the two individual slugs. This species of slug, commonly known at “leopard slug” or “great gray slug,” has as its scientific name Limax maximus, which appropriately means “largest slug.” Introduced from Europe, these slugs can grow up to almost double the length of the pair I saw, which were on a concrete step.

Two four-inch leopard slugs glide in tandem, apparently as a prelude to mating.

I watched the pair for a while, one following the other, with the head of the follower overlapping the tail of the leader. The phrase “get a room” came to mind, since their intent seemed obvious. But what do these slugs do then? How do they mate?

Slugs are hermaphrodites, with each having male and female characteristics, so an individual can mate with any other individual in its species. They mate by intertwining, sharing sperm to fertilize each other’s eggs. While, for most terrestrial slug species, this is accomplished on the ground, leopard slugs turn the process into more of a circus act, creating a thick rope of slime that they attach to a tree or structure and then hang from while they mate. A BBC article describes the mating process:

“Twisting their slimy bodies together, the large slugs dangle upside down from a glittering rope of mucus, slowly rotating. Then, out of the molluscs’ heads emerge large, blue, tube-like growths that wrap and writhe around each other.”

Those blue “growths” are actually penises, turning the circus act into a writhing tree ornament (see the BBC website). Having read about the leopard slug’s mating process, I wish I’d had more time to watch the two amorous slugs I saw.

These slug eggs were laid by an unidentified species under a rotting piece of wood. By Pam Owen

This is not the largest species of slug I’ve encountered. Decades ago, on a guided hike I took in Mt. Ranier National Park, the ranger leading the hike found a large banana slug, one of the three species in this genus, Ariolimax. While I don’t remember the exact size of the slug, I do remember it was larger than the leopard slugs I saw recently. Named for their bright-yellow coloring, banana slugs, depending on the species, can grow up to a foot long and live up to seven years.

The ranger told those of us on the hike that the Native Americans in the Northwest used the slime of slugs in this genus to treat toothaches, since it contains a mild anesthetic. Holding up the slug, the ranger asked if anyone was willing to try the numbing effects of the slime by licking it. Apparently, I was the only one curious enough to try it out. While not having much of a taste, the slime did indeed numb the tip of my tongue a bit.

Slugs were also eaten by native peoples and German colonists. I’ve eaten snails on many occasions, preferring them sauteed in garlic butter and paired with a nice, dry white wine — or with ginger ale, as I first ate them at a US officers’ club in Germany when I was a around three years old. But I’ve never consumed a slug. I hear they are good pickled.

© 2017 Pam Owen

Pam Owen
About Pam Owen 343 Articles
Writer, editor, photographer, and passionate nature conservationist living in Rappahannock County, in the Blue Ridge Mountains of Virginia. Two favorite quotes: By E.O. Wilson, who coined the term "biodiversity," "Nature holds the key to our aesthetic, intellectual, cognitive and even spiritual satisfaction”; by Douglas Adams, “I love deadlines. I love the whooshing sound they make as they pass by.”