Slugs are commonly known as shell-less gastropod mollusks and are able to cause enormous damage in many vegetable, ornamental and fruit crops. They feed on plant tissue located both aboveground and underground and can devour the equivalent of half their body weight within 24 hours.
Maximum damage occurs during warm and humid periods when conditions are optimal for the slugs to feed. Damage caused by slugs can be divided into 4 kinds:
In very young crops, they hollow seeds, strip leaves and eat roots and emerging cotyledons.
In older crops, damage to flowers, tubers and roots lead to a serious reduction of quality.
Feeding damage permits the entry of many kinds of plant diseases.
Mucous secretion, especially in flowers and salad crops also results in loss of quality.
Slugs have brown to black elongated, slimy and shell-less bodies. They have 2 pairs of feelers on the head and a saddle-shape mantel on the back. Depending on the species, adult slugs are 30 to 150 mm long. When they move, they leave a trail of slime behind. Slugs need a humid environment in order to survive, reproduce and move around. 90% of the slug population can almost always be found in the soil. Only 10% of the population comes out at night to feed on plant material. Most slugs are hermaphroditic, meaning that a single individual has both male and female genitals. After 2 slugs have mated, they lay their eggs in groups of 15 to 50 in the soil or under plant waste. Slugs are able to lay eggs 3 times a year. Under favorable conditions these eggs hatch immediately. Under unfavorable conditions they can survive for a long period until circumstances improve. Normally, there are 2 generations of slugs per year. However, in a wet summer there can be more generations.
The most commonly observed species are the brown slug (Derocerus laeve), the grey field slug (Derocerus reticulatum) and the garden slug (Arion hortensis).