Little 1 inch mounds of dirt that won’t dissolve with a tiny center hole

Question

I have hundreds of little mounds of dirt (about 1-inch high) all over my yard and below the grass line. It’s like stepping on stones. They won’t dissolve over time. Aerating the lawn in the past, the slugs are gone in weeks. When I break off the mound, a tiny hole is in the center. I have to super rub them down with boots to break it up. It’s as if the mounds of dirt are mixed with cement to make them so tough. I thought maybe ants as the hole is so small, but I figure the grass would be infested and I’d see them all over. Using the mower is an adventure in off roading and walking barefoot is impossible. PLEASE, WHAT COULD IT BE?!?!. Thanks.

Answer 1

Sounds like it could be earthworms. With the dry weather, their casting mounds are not breaking up like they normally would. This article will help with the issue:
http://lawncare.about.com/od/turfgrasspests/a/earthworms.htm