A common springtime "problem" associated with earthworms is the movement of large numbers to places where they are unwanted, including onto sidewalks or patios and into swimming pools. Earthworms, especially "night crawlers" also may create casts and mounds that contribute to a rough and bumpy lawn surface.
No doubt, earthworms can be annoying. However, it is important to remember that earthworms are also beneficial and valuable to the overall health and tilth of the lawn. Their activity improves the growing environment by increasing air and water movement in the soil and they help decompose thatch. They also help alleviate compaction.
There are no pesticides labeled for the control of earthworms. Although some pesticides and fertilizers are known to have a negative impact on earthworms, none can be recommended as a control. Compared to the pesticides (especially insecticides) used two decades ago, today's pesticides have relatively little impact on earthworm populations, in part because of the registration process that examines adverse environmental effects such as mortality to beneficial, nontarget organisms (including earthworms).
Various lawn care practices can help reduce the problem of a bumpy lawn. Bumpiness in sparse, thin lawns will be less noticeable if a healthy thick turf is reestablished through reseeding with a species and variety suited to the site, and through proper fertilization, mowing and irrigation.
Mechanical means to reduce bumpiness will be necessary to eliminate existing roughness. Core aerifying, power raking and verticutting are all mechanical processes that will break down some of the bumps in the lawn. Roughness accumulates over several years and it should be gradually removed instead of all at once. Use of a heavy roller is not recommended. While rolling may remove some roughness, it also damages the turf by compacting the soil. Compacted soil reduces turfgrass vigor and eventually leads to a thinner lawn.
Although rough bumpy lawns and earthworms on the driveway are annoying, the destruction of earthworms is neither practical nor advisable.