This page contains links outside Washington State University which provide an option for finding further information. No endorsement of products or information at these sites is implied. Slugs often arouse the anger of gardeners because both they and their damage can be so visible. They aren't entirely villains. Slugs and snails do have a role in landscapes as recyclers of decaying vegetable material, and it would be a huge mistake to attack or try to remove the large yellow banana slugs that are native to Northwestern forests.
Some species eat aphids and small caterpillars, though far more dine on tender vegetation.
In the animal kingdom, they are classified as mollusks, relatives of squid and octopus. Even a random look around any maritime Puget Sound garden reveals several different species of slugs. And within the last 6 years or so, snails have proliferated too. I scoop them off the wall and toss them into the street hoping they will become escargot for crows. All types of slugs and snails can destroy garden plants, and the problem is particularly difficult in May and June when plants have soft, tender growth.