EARTHWORMS AS PESTS IN HOME LAWNS

S. Bambara, Extension Entomologist

General Information

Earthworms are clearly beneficial in soil for aeration, water penetration, thatch control, addition of bacteria, organic matter and other benefits. Most soils are probably lacking in worm populations and much has been written about the benefits of worms and using them for soil improvement. However, on rare occasions and in rare situations, earthworms may become undesirable. Earthworms are also a major food source for some species of moles and are the main host for certain cluster flies.

Several of the worm species found in soils are introduced species from other countries or continents. Some of our native species of earthworms may be being displaced by the introduced species Extremely high populations may disrupt roots or create so much upturned castings on the surface as to smother low growing blades and create a bumpy surface. Heavy rains may cause worms to be stranded on sidewalks and driveways. These worms will die quickly due to ultraviolet light exposure and drying.

It is possible that the reduced number of lawn insecticides available (and toxic to worms) for insect control has allowed worm populations to rebound. Current pesticides may kill the parasites and predators that reduce worm populations without killing the worms. Worms do not like highly acid soils and reportedly do not inhabit soils below 4.5 pH. Some soil acidification with ammonium sulfate might be helpful, but treat only based on recommendations following soil tests and consider the pH requirements of the turf.

Biology

Each earthworm is both male and female so any two adult earthworms can mate. Mating tends to take place on or just below the soil surface and at night. Soil and air moisture must be adequate. They can vary in size, but the common night crawler is about six inches long, segmented, possesses barely visible hairs, and a smooth enlarged band (clitellum) about two inches from the front end. Mating will occur during the spring and summer, or almost anytime that temperatures allow. Mated earthworms deposit fertilized eggs within a cocoon on or near the soil surface. Each cocoon will contain four or five eggs, but may contain more or fewer. The cocoons are oval and approximately 1/8 inch long., Eggs hatch in two to three weeks. Two to three cocoons may be produced in a year if conditions are good. Most of the complaints received in North Carolina have been in late Summer or early Fall. During the Winter, earthworms will migrate deeper in the soil. Night crawlers will mature in about one year and may live up to six years.

Control

There is no treatment threshold for earthworms. Threshold is determined by the tolerance level of the homeowner or lawn caretaker. Power raking or rolling of the lawn when castings are soft will usually even the soil. Grass clippings should be collected, if desired, to remove some of the food source. This, however, also reduces the return of organic matter and nutrients to the soil. There are no chemical pesticides for homeowners registered for treatment against earthworms. If you wish to avoid killing earthworms in your turf, consult the following links and choose insecticides least toxic to earthworms. Of the turf pesticides labeled for other lawn pests and still commonly used, carbaryl (Sevin) and imidacloprid (Merit) are very toxic to earthworms. A 2009 Kentucky study by Potter et al showed tea seed pellets very effective for deterring earthworms in certain turf. For a list of pesticides and their toxicity to earthworms, click here. Check the pH in the soil.  Earthworms prefer less acidic soils. Many earthworm problems also tend to be in less well-drained soils. 

Industrious folk may want to collect earthworms without chemicals by "grunting".

Interesting links:

Great Lakes WormWatch University of Minnesota
The relative toxicities of insecticides to earthworms of the Pheretima group (Oligochaeta), Mostert et al. Pest Manag Sci. 2002 May;58(5):446-5
Carbaryl-induced behavioural and reproductive abnormalities in the earthworm Metaphire posthuma: a sensitive model.  Gupta & Saxena. Altern Lab Anim. 2003 Dec;31(6):587-93

The Effect of Fungicides on Earthworms
Earthworm dissection - Watch an earthworm eat
Mole and Vole control & Orchard voles
Earthworms and Castings in Sports Turf
UC Information from Robert L. Bugg
Earthworm Science in the News

Recommendations for the use of chemicals are included in this publication as a convenience to the reader. The use of brand names and any mention or listing of commercial products or services in this publication does not imply endorsement by the North Carolina Cooperative Extension Service nor discrimination against similar products or services not mentioned. Individuals who use chemicals are responsible for ensuring that the intended use complies with current regulations and conforms to the product label. Be sure to obtain current information about usage and examine a current product label before applying any chemical.

Other Resources

• Back to Insect Notes
• Horticulture Information Leaflets(HILs)
• Plant Pathology Notes
• North Carolina Agricultural Chemicals Manual
• North Carolina Cooperative Extension Service

Published by North Carolina Cooperative Extension Service

Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University at Raleigh, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating.

ENT/ort-125   January, 2003

Web page last reviewed January, 2011 by the webperson.