Bay Nature magazineFall 2018


Bizarre Banana Slug Facts

September 30, 2018

Pick an eye

The banana slug has two sets of tentacles. Like almost all air-breathing gastropods, it has two small eye spots at the top of the upper tentacles, which can move independently to scan for danger. The bottom two tentacles are for feeling and smelling—both senses far more honed in the slug than its limited sense of vision.

Will eat anything

Banana slugs have a mouth on the bottom of the head, with a top jaw for clamping or cleaving and, like all mollusks except bivalves, a sharp-toothed tongue called a radula that grinds food and moves it toward the stomach. As for what passes through the radula, well, they’re slugs. They’re not picky. “It might be easier,” writes Santa Cruz–based author Alice Bryant Harper in her 1988 book The Banana Slug, “to answer the question, ‘What don’t banana slugs eat?’”


For several years in the 1980s there was a Russian River Banana Slug Festival. The event included slug races, and locally renowned chefs tried their best slug recipes on a panel of judges. The New York Times wrote the event up in 1989 and noted a particular judicial rebellion against former Scott’s restaurant chef Paul Pfau’s preparation of slug and vegetable aspic, i.e., suspended banana slug bits over beets, asparagus and kale.

Hole-istic breathing

The gaping hole on the right side of the mantle, called the pneumostome, moves air in and out of the slug’s single lung. It can be opened or closed depending on the weather and the slug’s hydration and oxygen level: A slug needing air can open the pneumostome widely; a dehydrated slug, or one caught in a heavy storm, can close the pneumostome completely.

Banana slug hygiene

They use slime to clean themselves. According to Harper’s The Banana Slug, debris that sticks to the slug’s body can be moved backward to the tail, where the slug will turn around and eat it.

Fleet foot

A banana slug moves by contracting and relaxing its muscular foot, generating a wave that propels the slug slowly forward. Opinions vary when it comes to ranking animals by speed, but University of Eastern Kentucky biologist Branley Allan Branson concluded the banana slug was the slowest creature on earth. Branson reportedly clocked a banana slug covering 6.5 feet in two hours, a speed of 0.000275 meters per second.


Banana slugs lay a few dozen eggs at a time in moist cracks, crevices, or holes. After one or two months the eggs hatch and the inch-long baby slugs emerge to look for food. This is a prime window for smaller predators like birds or shrews to eat them, before they get too large and slimy. They can live up to seven years and do not seem to do any better in captivity than in the wild.

Slugs aren’t a thing

Limax, the original genus to which the banana slugs were assigned, comes from the ancient Greek word for “slug.” The Ariolimax genus, seemingly meaning “air slug” (banana slugs breathe air, although so do many other so-called “pulmonate” gastropods), was separated from Limax in 1859 by a Swedish malacologist named Otto Mörch. The name “slug,” much like the name “toad,” is without taxonomic significance. All slugs are gastropods, but within that class the word represents a number of diverse, not particularly closely related animals that we have decided look the same.

On slime

Banana slug slime has interesting chemical properties, among them, it’ll temporarily make your tongue go numb. Traveling slime emerges from the banana slug as a dry granule, which inflates to 100 times its original size upon contact with water and provides a gliding surface for the slug to negotiate the zigs and zags of a forest floor.


The banana slug has a mucus plug at the end of its tail. It can generate a slime cord from this plug, which it then uses like a rappelling line to descend slowly from high places. The banana slug’s relative Limax maximus, the leopard slug, mates in midair while hanging suspended by its mucus strand.

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About the Author

Eric Simons is a former digital editor at Bay Nature. He is author of The Secret Lives of Sports Fans and Darwin Slept Here, and is coauthor, with Tessa Hill, of At Every Depth: Our Growing Knowledge of the Changing Oceans.