These are large worms that live several feet below the surface of our soil in our gardens & yards. They ingest the soil extracting nutrients from it and then excrete the rest of it. You may see them on the surface of your lawn for oxygen when it rains, or when the lawn has been watered well.

Some of the soil they eat is clay, and when they excrete the clay it may leave hard lumpy areas on your lawn.
They do not harm you lawn, in fact they naturally aerate your soil for you. Trying to kill them is not only unnecessary, it is impossible.

If you do want to try and rid your lawn of them: Aerate your lawn & then top dress your lawn with sand. 3-5lbs per 1000 sq ft. Do this a couple of times a year. Sand is dry and holds no moisture; the dew worms may try to find a new home elsewhere.