Released: April 03, 2002

Friend or Foe? Earthworm Control Unnecessary

MANHATTAN, Kan. – Even though earthworms are good for the lawn and garden, some gardeners may be disturbed to find small bumps or casts in their lawn caused by tunneling.

"If you have mounds of soil in your lawn that make it hard to mow, nightcrawlers may be the cause," said Ward Upham, Kansas State University Research and Extension Horticulture Response Center director. "These bumps are randomly spaced rather than a ‘run’ that is characteristic of moles."

Nightcrawlers surface at night when conditions are humid, to mate or feed, often leaving their fecal material behind in the form of casts, or mounds, of refined soil.

"The bumps on top of the ground are called ‘middens’ and are a mixture of plant residues and castings," Upham said "These middens may be used for protection and food reserves."

The middens are actually an indicator of a healthy active lawn. They form stable clumps or granules which reduce soil erosion. The tunneling aerates the soil, which assists the movement of water and nutrients to lower soil layers.

The process mixes organic material with the soil and reduces unwanted thatch build-up. Outweighing the disadvantages of castings, earthworms also provide soil drainage through burrowing.

Some homeowners claim this activity causes lawns to be lumpy, Upham said.

"Nightcrawlers actually help the soil, but may make it difficult to mow," he said. "Getting rid of the middens will be difficult."

Since earthworms are beneficial, control measures are not required. Upham said homeowners wishing to cure the bumpiness or reduce earthworm population have several options:

* Break up the mounds of soil with a lawn rake.

* Flatten the casts with a lawn roller.

* Reduce lawn watering.

* Encourage earthworm-foraging birds such as robins.

* Consider night time picking of the foraging/mating worms. Worms, once picked, may be transported and released in remote areas or sold or donated to fishermen.

* Place a screen over drainage holes of pots to prevent them from entering containers. Setting the containers on a layer of gravel also keeps earthworms from entering containers since they will not move through a coarse layer.

* Insecticides are not recommended for earthworm control, because the insecticide may also kill non-target insect predators which feed on lawn pests like chinch bugs and white grubs.

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K-State Research and Extension is a short name for the Kansas State University Agricultural Experiment Station and Cooperative Extension Service, a program designed to generate and distribute useful knowledge for the well-being of Kansans. Supported by county, state, federal and private funds, the program has county Extension offices, experiment fields, area Extension offices and regional research centers statewide. Its headquarters is on the K-State campus, Manhattan.

Story by:
Lucas Shivers, Communications Assistant
lshivers@oznet.ksu.edu
K-State Research& Extension News