The night crawlers love the sprinkler system you recently added. If you cut back on watering, they will probably decline to tolerable levels. Night crawlers and other worms are welcome visitors to most gardens because they are so beneficial; they aerate the soil and disperse organic matter through the root zone. Their presence will improve the quality of your grass, so it may be worth tolerating a few bumps and hills for a healthier lawn. Although many lawn insecticides may reduce the number of night crawlers in your yard, none is labeled for that purpose. Neighborhood children might want to collect the night crawlers for bait for fishermen.