Is there any way to reduce the number of nightcrawlers in the yard. Their...
Although nightcrawlers are considered a beneficial species, they can
cause problems when they are overly abundant in our lawns.
Here is an answer from another Master Gardener that talks about these critters:
The bumps you are seeing in your lawn are caused by earthworms, most likely nightcrawlers. These are highly beneficial organisms in the lawn because they aerate soil, allowing water and oxygen to penetrate more easily into the ground. Their feeding helps recycle nutrients and fertilizes the soil. Nightcrawlers also feed on thatch, a layer of live and dead plant material that can accumulate at the soil surface and reduce the penetration of water and fertilizer into the turf root zone. However, as nightcrawlers feed on soil and plant material, they leave behind a waste product called castings. Nightcrawlers deposit castings in their burrows or at entrances at ground level forming conical mounds at the soil surface. These mounds are most often seen in early to mid-spring when nightcrawlers are first active and again during fall. During late spring and summer, when weather becomes warmer, nightcrawlers generally move deeper into the soil and are not normally seen. Although these mounds do not harm turf, they do make the ground rough and uneven, sometimes making it difficult to walk on the grass. You can reduce the inconvenience the mounds cause by using a power rake (also called a vertical mower) to help knock them down. Early autumn is a good time to power rake, although you can power rake in spring once the ground is firm underfoot and before hot weather sets in. When you power rake in spring, it's also a good idea to apply a pre-emergence herbicide AFTER power raking to prevent annual weeds like crabgrass from becoming a problem. Power rakes may be rented from garden centers and rental companies. Another temporary solution is to use a roller to flatten the nightcrawler mounds. This may compact the soil, so rolling should be followed by core cultivation (lawn aeration) to reduce the adverse effects of rolling. Despite the nuisance of these mounds, you should learn to tolerate the nightcrawler activity. Treating them with an insecticide is strongly discouraged. The value nightcrawlers have in creating and keeping soil healthy far outweighs any problems caused by their mounds. Toni Koski
Here is a link that may help you control them:
I hope this is helpful. Please contact AaE again if you have further questions.