Yes, earthworms can be considered pests when they eat or invade large amounts of your lawn. Eating and invading large amounts of lawns reduces the effectiveness of chemicals applied to combat weeds. When the earthworms eat too much, they not only reduce the effectiveness of chemical control, but they also compete with your lawn grass for nutrients, water and sunlight. If you are concerned about the use of chemicals, you can prevent earthworms from turning your lawn into a carpet by installing a blanket barrier around your plants.