Creature Feature: The Banana Slug is Living Proof that a Slimy Little Gastropod Mollusk Can be Loaded with Charisma

The banana slug has two pairs of tentacles functioning as sensory organs. The upper, longer pair are periscope-like eyestems. The lower, shorter pair (above the slug’s mouth) is for feeling and smelling. Photo by Greg Bodi via Wikimedia Commons.

Can a small, slimy, shell-less, forest-dwelling gastropod whose diet includes animal droppings and other dead stuff develop an enthusiastic fan following? You’re darn right. Consider these facts about the banana slug:

• It’s the star of several community celebrations, including the nationally–publicized Russian River Banana Slug Festival.

• It’s the official sports mascot of UC-Santa Cruz, and ESPN Sports Travel has named it one of the ten best team nicknames in college basketball.

• It’s the name of an environmental musical group, the Banana Slug String Band.

• It provides the raison d’etre for the International Slugfest, an organized campaign to locate and document exceptionally large banana slugs.

• It’s one of the leading contenders (along with the geoduck and the giant Pacific octupus) for designation as the official state mollusk of Washington. Only a gubenatorial veto prevented it from becoming California's official state mollusk in the late 1980s.

We could go on, but the point is made. Banana slugs have charisma – loads of it. That said, it remains that they are odd creatures that most Americans know little about.

The Pacific banana slug, a cousin of the snail, is a shell-less gastropod mollusk belonging to the genus Ariolomax. This genus includes three main species -- columbianus, dolichophallus, and californicus – as well as two known subspecies. To the unschooled eye, of course, these differences count for naught.

Banana slugs grow six to ten inches in length -- making them the second-largest slugs in the world (after the Limax genus in Europe) -- and can live for as long as seven years. They are named for their roughly cylindrical shape and characteristic golden yellow color (often with dark spots). Banana slugs do come in other colors, including greenish-brown, nearly black, and even white. Though the less common colors may reflect the influences of diet, available light, moisture, age, health, and other factors, the basic coloration evolved to blend well with detritus and help slugs avoid detection by salamanders, garter snakes, raccoons, foxes, porcupines, crows, ducks, beetles, and other predators. Some predators avoid slugs so they won’t have to deal with the mucus coating (as by rolling the slug in the dirt).

Banana slugs are stenotopic, meaning that they can withstand only a limited range of variations in environmental conditions. The climate has to be reasonably mild because severe winter cold will kill them. They need moist environments because severe desiccation can kill them. Since detritus and related organic matter provides most of their food, rotting plant and animal material must be abundant. Mushrooms are a preferred food, but they’ll consume lichens, algae, fruit, seeds, and even animal droppings and carcasses

All things considered, it’s easy to understand why nearly all banana slugs live in the floor of temperate coniferous rainforests and similar rainy-foggy-damp habitats within the long, narrow, mountain-backed Marine West Coast climate zone that stretches along the North Pacific Coast. This encompasses a huge area extending from the Salinas Valley of central California northward through coastal Oregon, Washington, British Columbia (west of the Cascades), and southeastern Alaska. Only in a few places does this range extend inland more than a couple of hundred miles.

You can look for banana slugs in a number of national parks in the North Pacific Coast region, including Muir Woods National Monument, Point Reyes National Seashore, Redwood National and State Parks, Olympic National Park, the Fort Clatsop National Memorial unit of Lewis and Clark National Historical Park, and Sitka National Historical Park. The latter park is situated in the Alaskan panhandle near the northernmost outpost of banana slugdom.

Banana slugs are generally nocturnal, but they aren’t exclusively creatures of the night. You can often see them out and about in the daytime during chilly spells and the cooler rainy winter months. If it’s a relatively dry time of year, check out detritus near creeks, in tree root tangles, and in other moist places. You’re not likely to see slugs in their usual haunts during bad dry spells though, because they wait out those periods by covering themselves with mucus, leaves, and soil.

Wherever you find banana slugs, you’ll recognize them when you see them. Nothing in the forest looks quite like a banana slug. (See the accompanying photo.)

The two distinctive sets of tentacles on the slug’s head are superbly designed sensory organs. The shorter set is for feeling and smelling, and the longer set is for seeing. The dark dots at the end of the longer tentacles are the animal’s eyes. If you watch those eyestems while the slug searches for food or copes with obstacles, you can see them functioning like a periscope as they stretch up and down and turn in all directions. The eyestems can even be retracted in the blink of an eye. The mouth, which is situated between the lower tentacles, is equipped with a radula, a tongue-like organ covered with a seemingly countless number of tiny teeth.

The mucus coating that most folks call slime is certainly a signature attribute. It actually serves many useful purposes. In addition to helping the slug avoid dehydration, the mucus helps the slug slide along the ground on the muscular foot covering its lower body, protects the animal’s soft body from sharp rocks, twigs, and other hazards, and discourages predators with its foul taste and mouth-numbing anesthetic effects.

The slime also contains pheremones that help slugs find mates. Since the banana slug is a hermaphrodite -- each animal having both male and female reproductive organs – the task is not especially difficult.

The more we learn about banana slugs, the more we come to appreciate that their presence enriches and helps to stabilize the ecosystems they inhabit. By feeding on detritus, they help to recycle nutrients and make them available for new growth. Slug excretions not only provide nitrogen-rich fertilizer, but also help to disperse spores and seeds needed for forest plant regeneration. Since the banana slug’s ecological niche is not yet fully understood, we shouldn’t be surprised to learn that there are other praiseworthy contributions.

In the words of proud UC-Santa Cruz sports fans – and slug fans everywhere -- Go Slugs!

Postscript: Let’s be brutally honest here. Banana slugs are not universally loved, nor even appreciated, by many of the people who deal with them. During the rainy season they may squish under your feet on trails and walkways, invade yards, gardens, sheds, garages, and houses, and leave glistening slime trails all over the place. They‘ll get into the darndest places too, since they can climb walls, move upside down, and squeeze into small holes. BTW, if you want to hear some really over-the-top remarks about the species, just ask somebody who is not Bear Grylls to describe a banana slug's distinctive taste. Some people do eat them at festivals, you know, although only the Lord knows why.

Comments

Bob,

I am a huge fan of banana slugs. When I was a camp counselor at the Environmental Education Center in Point Reyes National Seashore, I'd show my excitement to kids when discovering one along the trail by getting down on my hands and knees and giving it a big fat kiss! I like to think of them as the west coast version of leprechauns!

Kerry

Kerry, thanks for reminding me that Point Reyes has banana slugs. I forgot to include PORE in my list the first go-around, but I've taken care of that now. BTW, although it's totally none of my business, I have to admit that I'm curious to know what your spouse or significant other thinks of your slug-kissing dispositions.

LOL! To quote, "she's A-OK with it!"

-Kerry

We are delighted that you have recognized and publicized our charisma. Thank you, thank you! ... Seriously, though, thanks for your great fun facts on our namesake, the banana slug. Keep up your great blog.

Geez, guys, at least you could have left us with a song......like this one:

I love these great little creatures! From the first time I saw one in the Olympic National Forest I was totally enamoured. I even have a life size tattoo of one!

I grew up on the Olympic penninsula and first saw the slugs when I was seven. I was over-awed! Never had I seen anything like that; I figured they must have come from fairyland or maybe Mars .... or something (Hey! I was seven, OK?) Bears, wolves, cougars, otters, weasels and others looked normal to me, I saw them all the time. But, the giant slug was rare and wonderful and often as big as my arm. (Like I said, I was seven.) I appointed myself as their defender and taught other kids not to harm them. I didn't then know what role they played in nature, but I knew that they had to be just as important as every other critter out there.

I commented about a banana slug I saw on the stairway from one of the beaches at Olympic NP. It had black spots and looked a lot like a ripe banana.

I would note that the UC Santa Cruz motto is generally "Slime 'em Slugs!"

They also have that T-shirt that made it into the movie Pulp Fiction.

Hey Bob,

I'm the Park Interpreter at Portola Redwoods State Park. The children I see through here, who I host programs for, are probabbly some of the biggest banana slug fans I have ever met. I get questions about banana slugs all the time. As a result, I have been doing a lot of research on the little guys, and I have learned a great deal, myself. I do, however, still have a couple unanswered questions.

First off; the analgesic effects. I have heard mixed accounts of this side-effect of the slime produced by the slug. I was curious about how you verified this, yourself. What sources did you find? Do you know what the chemical responsible is called?

Secondly; Parasites. I have also heard rumor that banana slugs are hosts to many different kinds of parasites, including a few kinds that can cause spinal and cerebral meningitis in humans. Clearly, this is very concerning considering all the slug-licking we have going on here. Are there parasites present in/on banana slugs? What kinds are found on them? What conditions could they cause?

I can't verify any of this without licking a slug myself, and I'm a tenderhearted hippie deep down inside; I would hate to be the cause of any discomfort to slugs, which are sensitive to the salts and acids that abounds so plentifully in and on humans. That and I really just don't want to go slug licking. If you have any information on this, and feel like sharing your sources, I would really appreciate it if you could email me.

Thanks for writing this totally rad article, it's been one of the more informative ones I've found throughout my long and arduous quest for banana slug knowledge.

-Audrey

Audrey,

Much as I love slugs and snails, I wouldn't touch them with a 10-foot pole, and I'm sure to keep my pets away from them too because at least some of the many species can harbor lungworm -- and who knows what else. I wasn't aware of this either until some friends in the UK and in Australia told me about the connection -- you'll find more info with a quick internet search, as I'm sure you've already done. It seems like most of the research has been done overseas, and I look forward to some being done in the US, as lungworm is prevalent here as well, and it would be hard to believe there isn't some connection. Even pythons in the Everglades are being found to contain lungworm on necropsy, and there are plenty of slugs and snails in south Florida -- both native and nonnative species. How this applies to banana slugs, of course, remains to be seen. Here is some info I found about the subject on exotic species that have invaded Hawaii:

http://www.malamaopuna.org/ratlung/needtoknow.php

http://www.malamaopuna.org/ratlung/ratlung.php

Audrey, I'm afraid that handling questions about analgesic effects and parasites associated with banana slugs is way above my pay grade. For what it's worth, I do think that licking banana slugs is a bad idea.

Hi Bob,

Thanks for writing some positive things about slugs. I've been calling this slug a banana slug but it's way bigger than 6-10 inches...:-)

http://solarbeez.com/2012/04/02/slug-control/

I linked your web site onto mine so people could get the real low down on slugs.

Pat

re: facts about the banana slug - you forgot one:

It's the animal of choice when comparing the attention span of (presumed) ADD sufferers to another (presumably notorious) ADD sufferer in the animal kingdom; like follows:

"she's got the attention span of a banana slug"

Hi, Thanks for the great article. I've never been able to confirm that the banana slug is actually the state mollusk. Everything I find says that the then-govenor vetoed the proposal back in 1988. Do you have a source that shows that we do have a state mollusk?

Thanks!

Nice catch, Susan. I fixed it. Traveler's fact checkers must have missed that one. As far as I can tell, the banana slug has not been designated the official mollusk of any state. Darn shame, don't you agree?