Lately, I have been getting many calls with people concerned with small mounds in their turf, making it difficult to mow, work or play in their yard. Most of the time, the issue is earthworms that are very active at this time of year. In my research, I came across this short piece of information on nightcrawlers, from the K-State Entomology department. I thought I would share this to give more infomation about these beneficial but sometimes annoying worms.
If you have mounds of soil in your lawn that makes it hard to mow, nightcrawlers may be the cause. These bumps are randomly spaced rather than a “run” like is seen with moles. Nightcrawlers are large worms (usually 4 to 8 inches or more). They belong to a group of earthworms known as deep-burrowers. The deep-burrowers build large, vertical, permanent burrows that may reach as deep as 5 or 6 feet. Nightcrawlers pull plant material down into their burrows which can be fed on later. The bumps you see on top of the ground are called “middens” and are a mixture of plant residues and castings (worm feces). These middens may be used for protection and food reserves. The burrows can have a significant positive effect on soil by opening up channels for water and air to penetrate. Roots also like these channels due to the ease of root penetration and nutrients found in the casting material lining the burrow.
Nightcrawlers actually help the soil but may make it difficult to mow. Getting rid of the middens will be difficult. Rolling the lawn while the middens are soft may help temporarily, but mounds will be rebuilt when nightcrawlers become active again. Also, there is nothing labeled for nightcrawler control. Some gardeners want to protect the nightcrawlers due to their positive effect on soils. Pesticides that may be used for other pests vary widely in their toxic effects on earthworms. Dylox appears to have no effect. Malathion may be slightly toxic while carbaryl (Sevin)and copper sulfate are extremely toxic. Avoid using the latter group while nightcrawlers are active if you wish to protect them
Alicia Boor is the Agriculture and Natural Resources agent for Barton County K-state Research and Extension. One can contact her by email at aboor@ksu.edu or calling 620-793-1910