Facts About Garden Worms

Earthworms contribute to healthy soil.

The lowly earthworm may not look like much, but it plays an essential, helpful role in your garden. Not just known as fish bait anymore, gardeners value these humble invertebrates as powerhouse composters, and an entire cottage industry has grown up around vermicomposting. "Wild" worms, living in the soil rather than in prepared composting bins, are even more valuable, enriching and conditioning the soil as they eat their way through it.

1. Classification

   • Earthworms are members of the zoological class Oligochaeta, part of the phylum Annelida. Annelids are segmented worms, including nightcrawlers and leeches, as well as earthworms. The University of Michigan's Animal Diversity Web asserts there are more than 3,000 species of earthworm. Some 220 species are in the family Lumbricidae, which includes the most common worms in North America.

   Anatomy

   • Earthworm species share a similar anatomy, differing mainly in the size and number of segments which make up their bodies. The first segment contains the mouth and a wedge-like protuberance that helps the worm force its way through the soil. Other segments house a brain and a series of heart-like valves that ensure the worm's blood circulates; each segment contains a pair of excretory organs known as nephridia, explains Earthlife Web's Gordon Ramel. The only organs to protrude from the worm's body are hair-like setae, used in movement.

   Reproduction

   • Although earthworms are hermaphroditic--having both male and female reproductive organs--they normally mate in pairs rather than self-mate. Ramel explains that the testes and ovaries have their own separate sets of ducts, on separate sides of the body. The worms secrete a mucous tube into which the eggs are fertilized; the tube forms into a cocoon which, depending on the species, is left under ground or attached to water plants.

   Benefits

   • Matthew Werner and Robert L. Bugg, of the University of California Sustainable Agriculture Research and Education Program, observe that not only do earthworms convert leaf litter and other organic material to rich topsoil, but they also improve the soil's drainage and texture. Their movement through the soil lightens it, creating tiny passages for air, water and plant roots to penetrate and providing a habitat for helpful soil microorganisms. Worms enrich the soil as they eat and excrete tiny particles of decomposing material. Some species--known as epigeic worms--live near the surface and break down surface leaf litter; others--endogeic--live further down, breaking down decaying plant roots.

   Expert Advice

   • Karin Grobe, writing for the County of Santa Cruz Home Composting Program, recommends attracting worms by improving the soil. Her successful efforts to attract helpful worms began with loosening the soil with a pitchfork to a depth of about 6 inches, and working in a 3-inch layer of compost. She continues to mulch the ground around her plants with compost as well. These practices improve the soil while providing an ideal habitat for worms, which continue the soil improvement.

   Warnings

   • Worms used for vermicomposting, often red wigglers or "manure worms," are epigeic, living near the surface. The worms in your garden are more likely to be endogeic species, often known as "field worms." Therefore, Grobe warns against moving worms sold for composting into your garden soil, especially if you live in a warm, dry climate, because they may starve or overheat before finding sufficient surface matter to eat. Similarly, Werner and and Bugg caution against deep tilling, which can destroy worm populations by lifting deep-dwellers up to the surface and burying shallower-dwelling worms too deeply. Some pesticides can also kill earthworms.