It's not pretty. Those few slugs you see glistening in the beam of your hand-held light are just the tip of the iceberg, explained Glenn Fisher, an Oregon State University entomologist who is studying slugs that are agricultural pests in Oregon's Willamette Valley. The rest are underground digesting food, laying eggs and feeding on rootlets and endosperm of seeds. Not all our slugs are pests. Many, including the infamous quarter-pound banana slug, are native species that play important roles in our ecosystems, serving as seed and spore dispersers, nutrient recyclers and soil builders.
Slugs are food for many other creatures, including garter snakes, spiders, ground beetles and birds.
It's the non-native species of slugs that spell trouble for home gardeners and farmers. There are 10 species of pest slugs in Oregon. All but one of these, the tiny marsh slug, were accidentally introduced from Europe or Asia. Hitching a ride on imported plant materials, these foreign slugs left many of their natural predators back in the old country. They have flourished in their New World habitats.