Annelids are the segmented earthworms (or nightcrawlers) many people see in their gardens. In addition, the family includes such creatures as leeches and a number of sea worms. Since sea worms and leeches aren't likely guests in the landscape, the gardener typically pays more attention to earthworm activity than any of the other annelids. The two most common earthworm species on the U.S. are the common earthworm and the red earthworm. Earthworms are usually a sign of healthy soils because they prefer soils rich in organic matter.
The Worm Turns
Earthworms help your lawn because they are natural aerators. They create tunnels up to 7 feet deep under the soil surface that allow for better water, nutrient and oxygen penetration. Greater water penetration means roots grow deeper into soils than they would with just surface moisture, and increased oxygen in the soils improves beneficial soil bacteria. Worms also turn and mix the earth, creating looser soils that drain better, preventing erosion and reducing the amount of supplemental irrigation needed. Earthworm activity prevents soil compaction.
Earthworm Castings, Nature's Fertilizer
Earthworms release an excrement which gardeners often refer to as castings. It's a crumbly, finely textured substance that resembles soil but looks somewhat more pebbly. These castings are nearly odorless and contain water soluble nitrogen, potash, potassium, magnesium and a number of trace elements as well as beneficial microorganisms; all of which benefit grass. Castings also contain more than 50 percent more humus than normally found in topsoils, which enriches the soils. This organic fertilizer will not burn lawns as many inorganic fertilizers do.
The Organic Farmer's Friend
Earthworms have long been a staple part of organic gardening because they utilize and convert decomposing waste and plant litter into castings that can be added to soils. For the home gardener, thatch is the organic debris produced in lawns that builds up faster than it can be broken down. Earthworms help decompose thatch and make the subsequent nutrients available to the lawn and increase the likelihood that fertilizers and irrigation will actually reach the soils.
What Worms Like
Because of all the benefits, many people would like to attract more earthworms into their landscape, including their lawns. Earthworms live where there is adequate food, moisture, oxygen and a favorable temperature. Earthworm food includes animal manure, compost and mulches. Moisture should be about the same level as in most gardens, but not soaking. Do not use water from a water-softening system, as the salts will kill the worms. Do not use pesticides containing aldicarb, carbaryl, carbofuran or benomyl, and avoid soil fumigants. Avoid inorganic fertilizer, but especially those containing ammonium sulfate.