Slug Species

Slugs are among the best adapted molluscs to life on land. Tolerant of dry conditions and able to  survive compression, they are less dependent on calcium salts than their shelled cousins. More than 125 species are recognised in Europe. 

The most common species are outlined below:

Important species:
Broadacre crops (cereals, potatoes,OSR, etc) are at risk from two species in particular:

Grey Slug
Deroceras reticulatum

The slug is the biggest pest of crops in Europe
Size: 3.5 to 5 cm
Colour: Beige or brown with small dark patches
Foot: Same colour as the rest of the body
Movement: up to 4 to 5 metres during the night.
The grey slug is a pioneer species, colonising new
areas. Active from 0.80°Cto 20°C
Nutrition: 30 to 50 mg per day
Young: Pink of reddish/brown
1 to 5 mm long

Of all slugs, the field slug is probably the most likely to cause problems for arable farmers. It is a specialist on surface feeding and is a keen feeder on cereal crops, but will often attack brassicas and OSR. Further information can be found in the crops section.

Black Slug
Arion hortensis, Arion distinctus

Found less frequently in fields.
Size: 3 to 4 cm
Colour: Black
Foot: Orange
Movement: 2 to 3 metres at night,on the
surface and in the soil. Rarely active below 5°C
Nutrition: same as the field grey slug
Young: Grey bluish 4 to 5 mm long
It is a small (up to 3cm/1 inches in length), black slug with a pale strip on its side. They have no keel and both the sole and mucus are either yellow or orange in colour.

This slug feeds both beneath and on the surface therefore posing a threat to leaf, root and cereal crops. Most commonly they will attack the stems at ground level, particularly during emergence. As a good burrower it will also often attack roots such as beets or turnips and is well known to potato growers as a major pest, as it will feed on both the tuber and the foliage. Capable of penetrating the soil to over a metre, no crops are safe from this slug.

The Keel Slug
Tandonia budapestensis

The keel slug can grow up to 6cm/ 2 inches in length and is usually dark grey/pale green in colour. Its keel has a yellow/orange strip along the ridge and the foot is pale. Its mucus is colourless.

The keel slug favours conditions underground, and is often responsible for the early devastation caused by slugs feeding on drilled seed. Large enough populations during germination can lead to serious crop loss. It is also a great lover of potatoes and as it spends most of its time beneath the surface it can be difficult to control.

The Garden Slug
Arion ater

This slug is one of the biggest species and has been known to grow up to 20cm/8 inches in length. Colour can vary enormously from red, white, orange and grey though most, as you'd expect, are black often with an orange fringe. This slug has no keel and its skin is furrowed and textured. The sole is pale and mucus white.

The black slug does not cause as much damage as the previous three species, but will attack seedlings in spring.
As well as crops and plants all species of slug feed on earthworms, so controlling populations is also important in helping to maintain good soil quality.