Nightcrawlers are a species of worm that thrive under many lawns. Most people consider nightcrawlers of benefit to their lawns, but sometimes too much of a good thing can prove to be a problem. If your lawn has too many nightcrawlers and their castings are making the surface of your lawn difficult or uncomfortable to walk on, or making it look unsightly, then you may want to rid your lawn of its nightcrawlers.
Power-rake your lawn to remove all old worm castings.
Thoroughly deep-water your lawn. This could take several hours. Poke into the ground to see how deeply the water has penetrated. You want at least the top 3 inches of the ground saturated.
Apply liquid carbaryl (Sevin) insecticide to your entire lawn following the manufacturer's instructions for getting rid of sod webworms (nightcrawlers are not specifically mentioned but they will be killed). Apply the insecticide in the evenings for best results, as worms tend to come to the surface of the lawn in the cooler hours of the night.
Do not water your lawn for at least 3 days following the application of the insecticide.
Check your lawn for new worm castings after two weeks. If new worm castings have appeared then repeat steps 2 through 4.