Everything You Need To Know About Slugs

Slugs are often viewed as a garden nemesis. But it is important to understand that while they can be a pest, they can also be beneficial in your garden. Your goal, in an organic garden, should not be to eradicate them altogether. Rather, it should be to manage any issues and to to keep their numbers in check.

We’ve already covered How to Get Rid of Slugs Naturally in a previous article. But in order to better understand this common garden creature, let’s take a look at them in a little more depth:

What Slugs Might You Find in a UK Garden?

There are a number of slugs that are common and widespread in our gardens. The UK is home to around 30 Gastropod species. Slugs have lived in the British Isles since the last ice age, and there are several common types you’re likely to see as you garden. These include:

• The garden slug (Arion hortensis).

• Great grey slug (Limax maximus).

• Large black slug (Arion ater).

• Yellow slug (Limax flavus).

The garden slug is up to around 3cm long, with a bluish black back and an orange underbelly.

The great grey slug is up to around 16cm long. Pale grey with darker spots, it is also known as the leopard slug.

The large black slug is up to around 14cm long, and is typically jet black in colour but may also have an orange frill.

The yellow slug grows to around 13cm long and is easily identifiable due to its yellow colouring.

Where Are Slugs Found in a Garden?

It is believed that the average British garden will contain around 20,000 slugs – typically more than 200 slugs per square metre. You might not always see them, but they will likely be there nonetheless. Slugs can be found anywhere where there is a temperature over 5 degrees C. In cold, dry weather they tend to stay deep below the soil. In fact, around 95% of the slugs in your garden are to be found below the soil surface.

The Life Cycle of Slugs

Slugs are hermaphrodites, but must find a mate to exchange sperm before they can reproduce. 95% of the slugs in your garden are underground. They lay 20-100 eggs multiple times every year, and it is not unusual for a single slug to have around 90,000 grandchildren!

Slugs lay their eggs below the soil or in moist crevices. Climate conditions will determine how quickly these eggs develop. The warmer the weather, the more quickly the eggs will mature and hatch. It takes around a year for slugs to mature into adults, and once they reach adulthood, slugs typically live for a couple of years.

Slug Anatomy

Slugs have soft, elongated bodies that can stretch out and fit through surprisingly small spaces. They have heads with two pairs of tentacles that can be retracted. The top tentacles are longer and have eyes at their tips that can detect light but don’t provide an image. The lower tentacles are detectors of smell. Both pairs of tentacles are also sensitive to touch. They can be regrown if they are lost.

Behind the heads are fleshy lobes known as mantles. An opening in the mantle leads to a slug’s single lung. An anus and genital opening are beneath the mantle. Rather than a single structure that could be described as a brain, slugs have ganglia, or ‘knots of nerves’ located around their body. These form a nerve network.

What Do Slugs Eat?

Gardeners who have experienced plant losses due to munching slugs are no doubt already very familiar with the habit of these pests to eat leaves, and sometimes also stems and roots. Certain slugs consume over 500 varieties of plants and vegetation. They can consume around forty times their own weight in just a single day!

But you may not be as aware that in addition to eating living plant material, slugs may also eat a wide variety of other things. For example, they may eat decaying matter and plant debris – playing an important role in nutrient ‘recycling’. Slugs may also eat fungi, earthworms, and other soil biota below the ground. Certain species also eat dead animals, and some even eat other slugs.

You might to surprised to learn that slugs are aided in consuming plants and other food sources by their teeth. They have 27,000 of them! Slugs have so many teeth because they do not chew before swallowing. Instead, their food is passed by a ribbon-like band of microscopic teeth which is known as a radula. The radula acts like a circular saw which cuts through vegetation and other things they eat. When the teeth in the radula wear out, new teeth move forwards to replace them,

What Eats Slugs?

There is some good news for gardeners trying to keep slug numbers down and trying to protect the plants that they grow. This good news is that there are plenty of slug predators living in the UK. Here are some things that eat them in a garden:

• Hedgehogs

• Moles

• Frogs

• Slow worms

• Birds (blackbirds, thrushes etc..)

• Ground beetles

• Centipedes

• And occasionally other slugs.

Keeping chickens and/or ducks in your garden can also help you to deal with a slug problem. And nematodes can also be used to kill slugs if you experience a population explosion.

What is Slug Slime and Why is it Produced?

Aside from eating our precious plants, another reason why so many people hate slugs is because of the disgusting slime they excrete. Slug trails are certainly not the most appealing of sights, and accidentally touching it can be revolting.

But slug slime is essential to keep slugs soft bodies from drying out, which they quickly do if not protected. It is also used by slugs to get around. The slime allows slugs to move around, and to climb without falling. And also protects them from injury when they travel over rough surfaces. It also helps them to navigate. The smell of their own particular slime, interestingly, helps them find their way around, and to retrace their steps to their base or a good food source.

The slime is composed of mucins, water and salts. It has a number of interesting properties. It is hydroscopic (absorbs water), has the ability to change its consistency when pressure is applied, and has elastic properties.

Not only is slime interesting. It also contains substances that can be beneficial to human beings. This slimy substance contains hyaluronic acid, glycoprotein, proteoglycans and antimicrobial and copper peptides. These are all substances used in beauty products, and are proven to be beneficial to the skin. This might not be enough to make you reconsider your revulsion, but it is interesting to think about nonetheless.

These creatures are never going to be a gardener’s best friend. But they are fascinating creatures, and knowing more about them can help you see that they, like all the other creatures, have a role to play in your garden.