Tag Archives: Snails

Did you know that snails have thousands of little teeth?

Teeth of a sea slug – walking sea hare (Aplysia juliana).

Snails and slugs can eat practically everything. Some eat fresh plants, to the despair of gardeners, me included. Others eat live animals, such as earthworms or even other snails, animal waste, rotting vegetation or fungi. Some species eat one type of food, others are less picky, but practically all lands snails and slugs use their tiny teeth when feeding.

Snails* don’t chew their food before “swallowing” but scrape it up and rasp it using a structure called radula. It is a somewhat similar to our tongue, but covered with many rows of tiny teeth. The snail sticks its radula out to scrape the food. If the food is in a larger piece, e.g., a leaf, snails can cut it with their jaw (snails only have an upper one) before rasping it.

Snail using its radulae to obtain food – teeth shown as zig-zags

The number, size, shape and distribution of the teeth on radulae differ between species. Some snails have more than 100 000 teeth. The properties of the teeth depend on the type of food a snail eats. The shape of the teeth can also vary across the radula.

Radula and individual tooth of a predatory ghost slug, Selenochlamys ysbryda
Teeth of an omnivorous garden snail Cornu aspersum

The teeth are made of chitin – the same biopolymer from which the external skeleton of insects is made. They can also be hardened by minerals like iron, silicon, calcium or magnesium. the teeth at the front of radulae are used the most and thus wear out the fastest. But new teeth are constantly growing at the back, to replace the worn ones.

Snails grazing on algae from a hard surface (like glass) leave a characteristic trail:

 While on a soft fruit or mushroom, they leave less regular marks:

The text above refers mainly to land gastropods (snails and slugs) as all of them (with one known exception) have radula. But this structure is present in many other molluscs, for example aquatic gastropods and cephalopods like squids and cuttlefish and in reduced form in octopuses.

* For a better flow of the text I only write snails, but I mean snails and slugs unless specified otherwise.

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Photos (in the order of appearance): RME-OT Caracas- Venezuela; Debivort; Amgueddfa Cymru; Krings et al. 2019; Magdalena Kozielska-Reid (two last photos).

Did you know that snails and slugs use different gaits to move on different surfaces?

I often battle slugs and snails, because they eat the vegetables in my garden. However, recently I decided to take a closer look at them, especially the way they move. I have read that land snails have two basic gaits – adhesive crawling and loping. I decided to check that with my own eyes, which resulted in the photos and videos in this entry (taken with a phone so excuse the quality).

Land slugs and snails move by contracting the muscles in their foot. But contractions alone are not enough. They also need mucus, which acts partly as a lubricant – aiding sliding – and partly as glue – to stick to the ground so that the snail doesn’t slide backwards*.

On smooth, non-absorbent surfaces such as glass or plastic, snails practically always move by adhesive crawling – their entire foot sticks to the ground, and after passing, the trail of mucus is continuous.

Snail crawling on glass. Its movement is uniform and the whole foot rests on the ground.

When a snail/slug moves on a rough, absorbent surface (wood, bricks, concrete) it often lopes. It regularly lifts its head up and then lowers it back to the ground. As a result, the foot forms arches and only partly adheres to the ground. The position of each arch relative to the ground is constant and it looks a bit as though the snail is sliding on an invisible bridge. This type of gait causes the mucous trail to have breaks in it.

A snail loping on wood. The snail regularly throws its head upwards and its body forms arcs above the ground.

Snails generally move more slowly over rougher surfaces, with approximately the same speed for both gaits. Research suggests that loping is a way to save mucus when crawling on such surfaces.

A trace of mucus after the passage of a snail – first continuous after adhesive crawling, and then with breaks after loping.

Much of the research on the movement of snails has concerned the crawling gait, because the experiments were conducted on smooth surfaces – glass and plastic that allow observation of the snail from below. Therefore, it is not certain whether all land snails and slugs can lope. However, the snails that have been specifically tested could.

I decided to check the gait of snails and slugs in my garden. I found various species and watched them on different surfaces. I observed mostly adhesive crawling on glass and loping on wood. So, my observations were in line with expectations. Unfortunately, I also saw great grey slugs on the floor in my house – on laminate flooring they moved using adhesive crawling. On concrete and old metal, I often saw slugs and snails raising their heads, but I was unable to clearly identify the foot arches, and the trace of mucus was not clearly visible. More research is needed …

I encourage you to observe slugs and snails moving on various surfaces. You will surely find different species in your garden, or a nearby park, forest or meadow. I am curious what you’ll see and I invite you to share your observations in the comments section below this post.

Signs of loping snail – its head regularly rises above the surface, the foot forms arches and the mucus trail is discontinuous.

* Snails’ mucus is a non-Newtonian fluid – under low stress it is very sticky and helps the snail adhere to surfaces. Under stress (caused for example, by contractions in sections of the snail’s foot), the mucus liquifies, allowing the slug to slide.

You can find more of my snail and slug videos here.

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