The many species of these mollusks, which vary in size and color, thrive in moist, shady surroundings. Slugs and snails are mollusks, the same family of creatures claiming oysters, octopus, squid and clams. There are more than 60,000 species of snails and slugs. Snails have a shell and slugs don’t, but both secrete a slimy mucus on which they glide along) leaving telltale silvery trails. The pests feed at night and on overcast days; when the sun shines they go under cover. Slugs and some snails burrow into the soil, while other types of snails hide in debris or on plants. If conditions are too dry, a snail can seal itself in its shell and remain dormant for up to 4 years.