For the love of snails and slugs

After arthropods, molluscs – the group that snails and slugs belong to – are the second biggest phylum of animals on the planet. In the UK alone, there are 100 species of land snail, and that doesn’t even include the freshwater snails that live in our rivers and lakes. On top of this, the UK is also home to 46 species of terrestrial slug.

Where to find snails and slugs

Snails and slugs need to be wet, so you’re most likely to see them when it’s raining. They don’t like it when it’s too hot or too cold. If it gets too dry, snails can go into a dormancy called aestivation, or if it gets too cold, they might hibernate.

There are snails and slugs everywhere! If you have a garden, you’ll find them hiding under bricks and behind pots or resting in window boxes and compost heaps. If you live in an old house, you might even find them inside your basement or kitchen.

Look at snails closely and you’ll notice they come in many different shapes and sizes. Every garden is probably home to a common garden snail, but depending on where you live, there could be other species too. 

If you’re on a walk, you’ll find different species in the leaf litter than on the bark of a tree trunk. You’ll also see different species on a woodland walk compared to a stroll across a chalk downland.

Are slugs just snails without shells?

‘I’m always amazed that people hate slugs so much. I don’t know what a shell does to a snail to make it lovable,’ says Jon. 

Slugs actually do have a shell, but it’s internal. Their shell has been reduced so much through evolution that in most species it’s found under an area of thick flesh on the back of the slug’s head known as the mantle. However, there are a few slugs, including two UK species of Testacella, that have a relic of a shell on the end of their tail. 

Slugs have lost their shells over time, Jon says, and it’s probably happened many times throughout evolution. ‘This means some slugs are more related to snails than they are to other slugs,’ explains Jon. 

‘People may wonder why you would lose your shell because most snails can retreat into it and be protected from predators and dehydration.’  

‘But there’s a biological cost to making a shell. You need a lot of calcium, and it takes energy to make,’ explains Jon.

Shells are also heavy and add weight. Plus, if you live underground, like lots of snails and slugs do, a shell gets in the way when you’re trying to squeeze through gaps.  

How do slugs and snails sense the world?

Snails and slugs sense the world very differently to us. They can’t hear like we do, but they may be able to sense vibrations with their bodies. In fact, touch is one of the main ways they sense and feel their way through the world.

They also have chemosensors that are a combination of smelling and tasting. Using this sense, snails and slugs can search for food by following trails. To them, the world is a rich mix of chemicals. 

This makes up for their limited vision. They can only see differences in light intensity and blurred outlines. As well as their eyes, snails have light-sensitive cells spread over their bodies that are responsible for the shadow reflex, which causes them to retreat into their shells if a shadow falls on them.

Slime time

Snail and slug slime acts not only as an adhesive but also as a barrier that prevents dehydration. If this wasn’t enough, it also has antibacterial properties that stop infections and help wounds heal. 

‘I think snail mucus is really fascinating because it has two properties that are seemingly at odds. It’s sticky, but it’s also a lubricant,’ says Jon.  

Snail slime is an example of a non-Newtonian liquid, which means when you apply a slow pressure it acts as a liquid, but when you apply pressure fast it acts as a solid. Snails and slugs move at a slow speed, which keeps their slime flowing as a lubricant. 

But slime is not just important in helping them move around, it’s thought that it might also have a role in mating and may contain pheromones that helps snails to find a partner. Some species even produce very bubbly, foamy slime to put off predators such as birds and small mammals.

What do snails and slugs do when it’s cold?

In winter, you might not see any snails, as it’s too cold for them. Instead, you’ll find them hibernating in a sheltered place such as a window box. 

Before hibernating, many snail species seal up the openings to their shells with a mucus plug so they don’t dehydrate or get eaten by predators. They then slow down and go into a kind of sleeping state.

You often find snails clumped together in this state. 

What can I do about slugs and snails eating my garden?

‘People often ask me how they can stop snails from eating their lettuces. But most species don’t eat living vegetation, they eat decaying or dead vegetation, and are important recyclers of nutrients,’ says Jon. 

‘Not all of them are going to eat your lettuces, though some certainly are! They’re part of our wonderful food webs,’ he adds. 

Jon suggests planting things that snails and slugs don’t eat or that you don’t mind getting eaten. He recommends not using molluscicides to kill them, as these might enter the food chain and build up in other animals.

‘Ultimately, you’re never going to get rid of the slugs and snails in your garden. So, I think you have to be a zen gardener, grow plants that will survive and learn how to live with them.’

‘Although that doesn’t stop me from going out in the middle of the night to try to remove and relocate them,’ Jon confesses.

How do slugs and snails eat?

Slugs and snails eat using a tongue-like structure called a radula. This conveyor belt of tiny ridges acts like a piece of sandpaper that the snail rolls over its food. 

‘You might see a leaf that’s been eaten by a snail – its rough radula taking off the top layer.’

‘Some snails even eat other snails! They use their radula to drill through the other snail’s shell,’ says Jon. These snail-killing snails have arrived in the UK on plants and in soil from tropical and subtropical countries where they’re naturally found. 

The wonderful world of molluscs

Snails and slugs are molluscs, a diverse group of animals that’s thought to have evolved over 500 million years ago. 

Along with snails and slugs the mollusc family includes chitons and bivalves, such as clams, mussels and oysters, as well as squid, octopus and cuttlefish – known collectively as cephalopods. 

Snails and slugs to watch out for