What is a Slug

Every gardener loathes their presence but, “What exactly is a slug?” I hear you enquire...

Black slug on a leaf

Black Slug  (Arion ater)

Gastropods and molluscs

Well, slugs belong to the large animal group called gastropods, from the Latin ‘gastro’ (stomach) and ‘poda’ (foot). You’re probably more familiar with the garden varieties of slugs and snails, but gastropods have diversified to colonise most habitats on the planet; from woodlands to deserts, and from high mountains to the deepest rivers. The most abundant forms are the marine gastropods such as sea slugs and snails.

But not content with being such a hugely diversified animal group in their own right, gastropods themselves belong to the even bigger family of molluscs, from the Latin ‘molluscus’ (thin shelled). It’s estimated there’re around 100,000 species of mollusc, and with the exception of the gastropods, all other classes are marine dwellers.

The giant squid, octopus, and cuttlefish are all members of the marine mollusc family, along with the more obvious forms such as clams, oysters, muscles, and other shellfish.

Snail without a shell

A slug is basically a snail without a shell, and did in fact evolve from the snail. This dispels the popular myth that snails came after as an attempt by a well meaning angel to cover up the fact that God made slugs when he wasn’t paying proper attention.

“I know...  I’ll give them a little house. That’ll make them look prettier.”

To this day, most slugs still have the remnants of that shell – called the ‘mantle’ – which is usually internal. A few species actually do carry a small external shell.

Losing its shell may seem rather an evolutionary dumb move as it did provide some degree of protection, but the slug had a cunning plan. You see, it can now slither effortlessly through the spaces between the soil; an almost impossible feat when carrying a cumbersome shell on your back. This opens up a whole new subterranean world for the slug to inhabit; a world safe from many surface dwelling predators that still prey on the snail.

Slug slime

A slug gets around using a sort of ‘muscular foot’, and because this is quite tender and the ground quite rough, it secretes a kind of mucus (slime) over which it glides. This slime is hygroscopic, meaning it absorbs moisture and becomes more efficient. It’s the reason why slugs prefer wet conditions; needing to produce excessive slime in drier weather can cause dehydration.

Useful tip

Don’t attempt to wash slug slime off your hands with water. Instead, rub them together and it soon turns into little balls that you can discard.

Slugs need to keep moist or they’ll dehydrate and die. It’s another reason why they’re more active during wet weather. It’s also why they’re largely nocturnal; to avoid the heat of the day.

Fascinating slug fact

Cluster of tiny slug eggs

Cluster of tiny slug eggs

Did you know; slugs are hermaphrodite. They have both male and female sex organs! The slug can mate with itself if necessary, and both sexes can produce clusters of tiny pearl-like eggs.

I guess that’s why there are so many of the little bugg beasties around!

Handy hint

Turn logs, stones, and pots to expose any eggs to the elements...  and to visiting wildlife.

Most slugs are harmless

Britain is home to around 30 species of slug and, contrary to popular belief, most cause little damage in the garden. Some are even beneficial, feeding mainly on decaying vegetation. There are only really four species that do all the damage, so it’s good to learn to recognise these few bad slugs.

Some species, such as the Field Slug, are surface dwellers, munching their way through your tender plants. Others, like the Garden Slug, also attack below ground, with potatoes and tulip bulbs being particular favourites.

A staggering 95% of the slugs in your garden are living out of sight below ground at any given time, which is why the totally organic nematode slug control methods are rapidly gaining popularity among gardeners. One particular nematode species is a natural slug parasite that also lives below ground.

Learn how to be a gardener

How to be a Gardener: book cover

How to be a Gardener

The ‘complete’ edition of How to be a Gardener combines both Book 1 and Book 2 of Alan Titchmarsh’s best seller into one helpful, but thick, volume. For me it has the perfect balance of down to earth information and inspirational ideas.

The first half of the book takes you from an understanding of how plants grow, through tools, simple plot layouts, advice on plant choice, and maintaining your garden; with the second half concentrating on garden design and more advanced skills.

Combining these two aspects of gardening – the practical and the aesthetic – provides much intellectual stimulation. You can begin small, dream, plan, and build for the future.

How to be a Gardener
Find out more

More books about gardening

What do you want to do now

Did you

A slug is essentially a snail without a shell

How to be a Gardener

by Alan Titchmarsh

How to be a Gardener: book cover

Alan Titchmarsh draws on his extensive knowledge and experience to bring you this comprehensive guide to being a successful gardener.

An essential reference manual for any garden owner – combining both Book 1 and Book 2 of this best seller into one helpful (thick!) volume.

How to be a Gardener
Find out more

Suttons Seeds logo

Over 200 years of gardening history

Suttons specialise in seeds, bulbs, and plug plants, plus a range of other gardening equipment.

Suttons Seeds

If you like this site,
why not tell your
friends about it