Charles Darwin wrote that “It may be doubted whether there are many other animals which have played so important a part in the history of the world, as have these lowly organized creatures.” The humble earthworm may not be on the top list when beneficial critters are mentioned, but its contributions to a healthy soil are numerous.
Earthworms are natural composters. Earthworms aid in the decomposition (recycling) of organic material. This results in improved overall soil structure, plant growth and reduced thatch buildup in lawns.
Earthworms aerate and loosen the soil by digging tunnels up to 7 feet deep, bringing mineral-rich subsoil to the surface with numerous smaller organisms that contribute to the health of the soil. Research shows that in 100 sq. ft. garden soil, earthworms may bring from 4-to-8 lbs. of dirt to the soil surface each year. The tunneling of earthworms aerates and loosens the soil allowing oxygen to penetrate deeper, which improves beneficial soil bacteria that contribute to plant health. That is why earthworms are called “nature’s plough.”
Earthworms ingest soil and digest the organic matter as they tunnel, producing castings. The castings increase the nutrient level and organic level of the soil. Nitrogen, phosphorous, potassium and other nutrients are produced daily for the use of plants. The equivalent of about 1/3 lb. of top grade fertilizer is produced per worm each year. Soil rich in humus can easily support 25 worms per cubic foot.
The addition of organic matter such as compost, manure, and mulches will attract earthworms by providing undecomposed litter as a food source. You may also purchase the common earthworm or "nightcrawler" (Lumbricus terrestris) and spread them around the garden a few per square foot.
Now for some other interesting facts about the humble earthworm:
• There are approximately 2,700 species of earthworms.
• The average life span of earthworms is species-dependent. Researchers have found that some species have the potential to live 4-8 years under protected growing conditions–meaning no predators and under ideal conditions. While individuals of Lumbricus terrestris can live for 6 years under ideal conditions, their lifetime is much shorter in the natural world.
• Given favorable conditions, one acre of land can contain more than a million earthworms.
• South Africa is reported to have the largest earthworm on record. It measured 22 feet from its nose to the tip of its tail.
• Most earthworms native to North America are thought to be extinct. The two most common species of earthworms in the USA are the common earthworm ("nightcrawler") and the red earthworm (Lumbricus rubellus). These earthworms were introduced from Europe during colonial times through soil in potted plants.
• The number of rings or segments of the body is species dependent. The common earthworm has about 150 segments while red worms have approximately 95.
• Earthworms are hermaphroditic (each individual possesses both male and female reproductive organs). However, earthworms are usually not self-mating. A mutual exchange of sperm occurs between two worms during mating.
Beneficials in the Garden & Landscape is an Earth-KindTM program coordinated through Extension Horticulture at Texas A&M University. Earth-Kind uses research-proven techniques to provide maximum gardening and landscape enjoyment while preserving and protecting our environment.
This web site is maintained by Master Gardener Laura Bellmore, under the direction of William M. Johnson, Ph.D., County Extension Agent-Horticulture & Master Gardener Program Coordinator.
All digital photographs are the property of the Galveston County Master Gardener Association, Inc. (GCMGA) © 2002-2006 GCMGA - All Rights Reserved.