Snail Slime
a substance as much eww, gross! as it is ooh, ahh!
Even if you've never seen or held a snail, you've probably heard about their slime. Not necessarily as infamous as their slug cousins, snail slime is actually more amazing than it is gross.
Snail slime, like all slimes and gels, is a liquid crystal, meaning it falls somewhere between a liquid and a solid.
Snail slime also has non-newtonian properties and is considered a yield-stress fluid. Yield stress fluids are fluids which act like liquids (i.e. they can flow and pour) only if they are submitted to some kind of stress, like being hit or pressed.
Think about that. This means that, when it's just sitting there, snail slime is more solid and glue-like. Only when the slime is compressed, like when a snail is moving on top of it and compressing the slime under the weight of its own body, does it become a liquid, acting as a lubricant that helps the snail move along smoothly over all kinds of landscapes.
Garden snails actually produce two different types of slime. The first is clear and liquid-like. This is the kind of slime the snail leaves behind as it moves, often refered to as the slime trail.
The other type of slime is similar but thicker, more viscous and elastic. The snail uses it to adhere to different surfaces, and it's super sticky. Using this form of slime, snails can crawl straight up a wall or move while hanging upside down. Snails can even adhere themselves to some surfaces specifically designed to be non-stick.
So, snail slime serves multiple purposes for its creator. It sometimes acts as an adhesive, allowing snails to literally climb up walls. It is also sometimes a lubricant, allowing snails to move with greater ease and protecting them from surfaces that are sharp, abrasive, or otherwise hard to move over.
It can also combine these two types of slime to function as a sealant, allowing a snail to curl up into its shell when its environment is too hot or dry, lubricating itself with one type of slime and sealing itself up inside its shell to preserve its own moisture. And, speaking of moisture, snail slime is also hygroscopic, meaning it attracts water. This is very useful for snails which, like slugs, can become very easily dehydrated by the conditions of their environment.
Slime trails left by other snails can also serve many purposes to other snails. When a snail discovers a slime trail left by another of its species, chemical indicators in the trail can tell a snail what direction the original snail was moving in, information about the sexual state of the snail and its potential as a mate (which you really want to watch more about), and it can also act as a food source for the traveling snail. In fact, snails can even feed on their own slime trails, the ultimate act of recycling.
These are all things we know about snail slime in the natural world, but there are a ton of things that we don't yet understand about snail slime and even more we're trying to design and engineer based on what we do know. People are using snail slime in a variety of skin care products for its anti-aging properties and it is an inspiring force in robotics as engineers try to learn from the "adhesive locomotion" to create machines that can move as smoothly as snails do over all kinds of terrains at all kinds of angles. All of this, just in the slimy secretions of the snail.