Based on your description—a 4-inch-high tower of mud balls with a hole in the center—this is most likely a crayfish burrow chimney.
Crayfish Burrow Chimney
What It Is
Certain species of burrowing crayfish build vertical mud “chimneys” at the entrance to their underground burrows. They roll small balls of mud and stack them around the hole, which serves as the burrow entrance.
Purpose
- Prevents flooding of the burrow
- Keeps debris out
- Regulates moisture and airflow
- Marks the burrow entrance
Characteristics
- Usually nocturnal, so it may appear overnight
- Found in damp, low-lying, or poorly drained lawns
- The underground burrow can be 6–36 inches deep, sometimes with a water pocket at the bottom
Impact on Lawns
- Generally harmless
- Can make the lawn slightly uneven if multiple chimneys appear
If your area has had recent rain or your lawn is soggy, this is the typical explanation.
If you want, I can also tell you how to safely identify if the crayfish is still inside the burrow.
