Melting snow and spring rain saturate soil, forcing earthworms up for air. Once soil pores drain, worms drill home, leaving piles of digested and extruded soil behind.
Known as "middens," these bumpy piles stand out on snow-flattened lawns. Until grass grows higher than the middens, many homeowners fear these worms are damaging their lawn. Nothing could be further from the truth. Earthworms continually release nutrients to plant roots, help aerate soil and enhance water infiltration through the soil.
Earthworms travel through soil, ingesting mineral and organic matter along the way. A worm's exterior tube of muscle surrounds a series of guts, along with five hearts, a brain with central nerve cord and a circulatory system. Soil minerals, fungi, bacteria and other organisms satisfy worms' nutritional needs. Worm castings (excrement) satisfy plants' nutritional needs. In turn, plants satisfy animals' (including humans') nutritional needs. The simple earthworm is a crucial link in the cycle of life.
Still, bumpy lawns can drive some homeowners crazy. Even while acknowledging that worms are beneficial in the long run, many people ask how they can kill this lawn "pest."
Luckily, there are no pesticides or products marketed to kill earthworms. Worms have many natural enemies, including birds, toads, snakes, centipedes and moles. Of these, only birds are likely welcome in suburban landscapes. Bird predation is limited, since worms typically emerge at night while birds aren't hunting. Only during or shortly after a soil-soaking rain are worms plentiful during daytime. So, natural predators are unlikely to significantly reduce worm populations.
Earthworms mate above ground, and peak mating seasons are spring and fall. With many trips out of and back into the soil, more middens appear during these times of year.
Areas with poorer soil host fewer earthworms, which can be a dilemma for owners of new homes trying to improve compacted subsoil surrounding their home. In a perfect world, worms could be extracted from established lawns and transported to new landscapes.
Until worms are given the respect they are due, practice tolerance. Middens disfigure spring landscapes but are soon hidden as grass blades grow. A few weeks of imperfection will pay off with more vigorous lawn later this year.