What Insects Leave Little Piles of Dirt in Grass?

Earthworms & Night Crawlers

• The red earthworm and the night crawler -- also suitable for fishing and commonly found in bait shops -- are the largest earthworm species in the U.S. Earthworms feed on soil organisms and plant detritus in gardens, speeding the recycling of plant nutrients that support healthy gardens. They do the same helpful work in your lawn, breaking down grass clippings and turfgrass thatch, which helps both moisture and oxygen penetrate more effectively. Recycling nutrients also helps fertilize your lawn -- earthworm tunneling and burrowing is the most effective core cultivation and aeration available.

Unsightly Side Effects

• For all the work night crawlers do, the tidy piles of waste or castings they leave outside tunnel openings are unsightly. Most common in spring and fall when night crawlers are typically active near the soil surface, these mounds can make your lawn uneven and hard to walk on. By late spring and during summer, when weather heats up, earthworms move deeper underground. There are some simple, sensible steps you can take to regain general use of your lawn, but resorting to pesticides isn’t one of them.

Avoid Pesticides

• Earthworms grow and reproduce slowly. Developing a large, healthy population of earthworms and night crawlers can take a lifetime to accomplish. The unwise or unnecessary use of pesticides in your garden or lawn can wipe out earthworms and greatly damage your backyard ecosystem in an instant. Apply pesticides only when needed and then only in spot applications. Use products least likely to injure earthworms. Avoid using pesticides after rain or lawn irrigation when earthworms and night crawlers are closest to the soil surface.

Minimizing Earthworm Impacts

• Apply a thin layer of compost to your lawn and rake it in, smoothing out piles of castings in the process. Repeat this process every week or so until the lawn has leveled out. It may also help to cut back on irrigation, especially if your lawn borders on soggy anyway. Let it dry out between watering because earthworms prefer very moist soil. They dislike acidic soils, or those with a pH lower than 6. In some locales, applying ammonium sulfate, ammonium chloride or other acidifying fertilizers can help cut back surface earthworm activity.