July 17/2024

 

Why Are Snails & Slugs So Slow?

By John Tooker, Daniel Bliss, & Jared Adam 

1/2/2024

atlasobscura.com

WANDER THROUGH YOUR BACKYARD OR walk along a stream & it’s likely you’ll see a snail: small, squishy animals with shells on their backs. Snails are found in water, whether in salty oceans, rivers, or lakes. They’re also on land: in forests, grasslands, & even your garden.

As you explore your yard or woods, you can also encounter slugs, which are slow-moving animals related to snails. They look like them too, except that slugs lack shells. Not only can you find slugs crossing sidewalks or on plants at the park—some are in our oceans.

All told, an estimated 240,000 species of snails & slugs live all over the world. But no matter what continent they’re on, or what ocean they’re in, there’s one thing they all have in common: They move slowly.

Here’s an example of just how slow they are: The World Snail Racing Championships, held in the United Kingdom, pits the quickest snails against one another in a “foot” race. The fastest snail on record sped through the course at a blazing 0.006 miles per hour.

Or to look at it another way, if you were that slow, it would take about 3 minutes to get a bite of food from your plate to your mouth.

Why is it that snails & slugs are in no hurry? As researchers who specialize in the study of plants & animals, we’ve learned the answer is more complicated than you might think.

Snails & slugs are members of a large group of related animals known as mollusks, which also includes clams, oysters, squids, & octopuses. Within mollusks, there’s a smaller set of related animals called gastropods; this includes snails & slugs.

Because they live in such diverse places, different gastropods have evolved to consume almost every type of food. Some species are herbivores—they eat living plants. Some are detritivores—they feed on dead or decomposing plants. Others are carnivores or scavengers—they eat other animals.

The lack of speed of snails & slugs can be attributed to at least 3 factors: how they move, what they eat, & what eats them.

First, while some animals fly, jump, or slither, snails & slugs move using what biologists call the “ventral foot.” But the word “foot” here can be confusing. A snail or slug foot is nothing like a human foot. Instead, it’s a band of muscle that runs along the underside of their body & is covered in sticky mucus. When contracted, this muscle ripples, sending tiny waves from the animal’s tail to its head. These waves compress the mucus on the bottom of the foot into a slippery liquid, allowing the snail or slug to glide over the ground or climb plants.

It’s a unique way to move, & it forces snails & slugs to go slowly because their speed is limited by the number of foot contractions & the amount of mucus they can make. And snails & slugs don’t need to rush to find their food, anyway.

Many animals, particularly predators, must move fast to catch a meal; a cheetah needs to outrun a gazelle, for example. But most slugs & snails eat plants, decaying matter, or marine animals, like sponges, which are anchored in place. None move around much, so dinner’s not going anywhere—no rush.

Nor do snails & slugs need to be fast to avoid predators. They’ve evolved other ways to evade mice, birds, shrews, and other enemies. Typically, snails withdraw into their shells to hide until the predator passes.

Land slugs hide in plain sight. Most are shades of gray, tan, or brown and blend in well with their surroundings. Predators simply don’t notice them. They also have an additional layer of protection. Land slugs are covered with a sticky mucus, similar to the mucus that lubricates their movement. But this version is so gooey that it can gum up the mouths of predators and make it hard to chew. Not to mention that most predators probably wouldn’t find the slime very tasty.

In contrast, sea slugs are often easy to see because they are colorful. But these bright colors advertise to predators that they should stay away, because the slugs are protected with nasty-tasting poisons.

Snails and slugs, small as they are, are big contributors to the health of their ecosystems. By feeding on seeds and young plants, they can control which plants grow in an area. By eating decaying matter, they help recycle nutrients that growing plants can use. And despite their best efforts, snails and slugs do often become food for other animals.

So the next time you see a snail or slug hanging from a plant, dawdling in your yard or gliding across a concrete sidewalk, stop and observe. Remember its remarkable biology, the unique way it moves and looks, and the many ways it benefits the environment.

And then, let them be. These small animals help keep our world running.

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