Snails and slugs are both from the mollusc family that once belonged in an aquatic environment. Although they have evolved into the annoying land-crawling creatures they are today, it gives us some clues as to which conditions they prefer.
For a snail or slug or snail to move, it needs to produce a slime that it can then drag its disgusting slimy self over. This leaves behind a silky slime trail, which many moons ago we'd wake up to in our sharehouse living room. Other than sharehouse rugs, snail and slugs prefer the young, tender growth of your seedlings and are most active when conditions are damp. These night feeders tend to be gregarious and return to the same resting place. While snail shave a protective shell, meaning they feel a little safer out in the open (as opposed to under my lowering boot), slugs don't enjoy the same protection and will burrow into the soil for shelter.