Answer: Worms are present in healthy soils and are considered beneficial critters. Worms aerate the soil and consume organic debris, leaving rich humus behind in the form of castings. The night crawler, Lumbricus terrestris, is a beneficial guy as far as worms go, tunneling into the cool earth sometimes to a depth of three feet. This activity benefits the lawn by reducing compaction and providing aeration.
Another smaller species has become quite a nuisance in the south. Their high populations and vigorous activity leave turf runners covered with their casting piles leading to decline of the lawn. These worms tend to come and go through the seasons and usually become less of a problem over time.
No pesticides are currently labeled for earthworm control in turf. Washing the castings off the turf with water after a period of high worm activity will help reduce the damage to your lawn. Don't be tempted to use a lawn roller which will compact the soil and negate the benefit that the worms are adding to your soil.
Some gardeners have to frequently rent lawn aerators, heavy gas-powered machines which remove 2" plugs of dirt, to loosen or aerate the soil. These plugs are left on the ground to decompose back into the soil. This costly process, which is often recommended twice a year on heavily compacted lawns, is being performed at no cost to you by your friendly night crawlers-a gift of nature perhaps.
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