Snails and slugs are the two groups of animals which are closely related, though the snail has a shell while the slug does not. Slugs can damage seeds, vegetation, flowers, fruits and vegetables when they feed.
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Adult size: about 1/2 - 5 inches
Typical damage on leaves appear around the margin, or if small enough the slug may consume the whole leaf. The effect of their feeding can be unsightly or absolute devastation to the plant. A sure sign of slug activity would be the slime they leave behind. This slime allows the slug to move, though can solidify allowing the animal to stick (and reliquify allowing him to move again).
Slugs thrive in moist conditions; they may be found under mulch, pots, heavily shaded areas, leaf piles, dense vegetation, anywhere that may retain moisture. During periods of drought, slug and snail activity may slow and the damage may cease. They lay their eggs in the cracks of soil, and when hatched, the emerging slug may do damage to seedling.