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SLUG IDENTIFICATION

To control any pest it is essential to know something about the beast. In this instance identification of the various types of slug is desirable, because not all of them cause problems in the garden. As explained later, overuse of slug poisons can be counter productive in that you risk killing off the predators that are helping to control your slug population. Such poisons should therefore be used, if used at all, only when and where a serious problem is seen to be developing, involving a slug species that is known to attack the crop you are growing. Once you have identified the species and can learn a little about its habits, you might well find that there are non-chemical options that are effective controls.

There are around thirty species of slug in Britain. Only a minority poses any serious problem and four of the worst and most numerous of these that cause damage in gardens are described below.

The Field Slug

The field slug is small - up to 4 cm - and usually grey/fawn in color with darker flecks. It has a short truncated keel or ridge on the back at the tail end. The underside, or sole, is whitish with a darker zone along the centre. The mucus is colorless or white. The field slug is a surface-feeding specialist typically found infesting lettuces and cabbages. In fact it eats almost all our crops, from carrots and beans to spinach and tobacco, from celery and tomatoes to orchids and cacti. It is a major pest of cereal crops and will even eat potato haulms.

The Garden Slug

The garden slugs are a group of small blackish slugs up to 3 cm, with a paler side stripe. They have no keel and are distinguishable from similar species by their rounded cross section. The sole is yellow or orange; the mucus the same color. As burrowers and surface feeders, the garden slugs attack both leaf and root crops. Typically they attack at ground level, severing the stems of young beans or marrow plants for example. They will also climb up and attack the heads of cauliflowers and many other plants or burrow down to eat the roots of turnips or beetroot. It is a major pest of potatoes attacking both tubers and foliage and has been known to penetrate the soil to as much as a yard's depth so nothing is safe from this slug.

The Black Slug

The black slugs can be very big: a length of up to 20 cm has been recorded. Its color is very variable - white, red, orange or grey are all common although black is most usual, often with an orange fringe. There is no keel, and the skin is coarse and granular. The sole is pale, sometimes orange, and the mucus is white. The black slug may rock from side to side when disturbed. The largest European land slug is the black keel back slug (Limax cinereoniger). It is its smaller relative, the grey or tiger slug, which was given the scientific name of Limax maximus, the largest or very large slug. Besides, the black slug is not always black. In contrary, there are many grey, even light grey, specimens to be found.

The Keel Slug

The keel slug is a larger species up to 6 cm. usually dark grey/olive in color, it has a keel, with a yellow or orange stripe along the ridge. The sole is pale, the mucus colorless. Typically it curves into a sickle shape when contracted. A burrowing specialist, notorious for its destruction of potatoes, it will in fact attack most root crops and is difficult to control as it spends most of its time underground.