Answer

Dirt Mounds in the Lawn

Question

I have little hills all over my yard. They are about 1 inch high and 2 inches in diameter. When I scrape the dirt back there is a little hole about the size of a fishing worm. These things are so bad that riding the mower across our yard is like driving in an old car without shocks down a gravel road. Can you please tell me what they are and what to do to get rid of them?
Betty Pigg

Answer

Insects, voles, moles, bees and other critters sure have been busy all over the country. I have received a large number of questions about dirt mounds and/or holes in lawns. In your case, because of the size of dirt mound and hole that you described I'm going to guess the culprit is an insect.

Do you live near a natural source of water? You could have been invaded by crayfish. Crayfish will relocate to a lawn when populations outgrow their habitat. The holes will be about 1 inch in diameter, 2 to 4 inches tall and made from balls of mud. These holes are formed by the crayfish digging down to reach water. They tend to resemble towers more than mounds. Eradicating crayfish can be tricky because they live in water and each state has different regulations about applying pesticides near water. If you think crayfish are the problem contact your local branch of the U.S. Fish and Wildlife Service to see what options are available.

Next on the list of suspects is the solitary or ground bee. While some bees are social, living in colonies with a queen, other bees are solitary, nesting and raising larvae alone. Some solitary bees are ground nesting. They burrow down into soil to make a nest. The soil mound is typically 2 inches tall and the hole is about 1/4 of an inch in diameter. Although they are solitary bees they will create nests close together where conditions are favorable. Loose soil in a dry, sunny location is a favorite spot. Solitary bees are gentle and helpful pollinators so I hesitate to recommend any action. However, if bees are indeed the problem it would seem that your situation is extreme. Start by closing up the holes by tamping down the soil. Or try sprinkling water in the area to encourage the bees to move on. If neither of these tactics work try a powder form of pesticide. Begin with something earth friendly like pyrethrin and move up to more potent controls if necessary.

Some bugs like cicadas and June bugs emerge from the ground in late spring and early summer leaving behind small holes and dirt mounds. This problem will correct itself as the season progresses.

Another ground dwelling insect is the cicada killer wasp. This wasp digs a 1-inch diameter hole for housing their larvae. The wasp hunts down a cicada, drags it back to the nest and leaves it behind as food for the larvae. I'm skeptical that this is your problem because they don't create mounds, just holes with dirt scattered around.

Earthworms also create mounds of dirt, but there are often no holes associated with their handy work. Most earthworm activity happens in the spring and fall or after a rain. Given the extreme quantity of dirt mounds that you describe, moles should also be considered.

Mole activity is evidenced by 2- to 24-inch volcano shaped mounds. The nearby grass may also be raised where the mole is tunneling across the lawn. There are several tactics you can use to rid your lawn of moles, click here to read a Q and A that discusses them.

Finally foraging animals such as birds, squirrels, raccoons, armadillos and skunks will dig holes in your lawn. These are usually medium to large in size with scattered dirt rather than mounds.
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