Imagine stepping outside after a rainy night and finding a strange mud tower in your lawn. Standing three to six inches tall with a perfect hole in the center, it looks like a miniature chimney built overnight. These formations aren’t random. They’re carefully constructed from small mud pellets stacked vertically. And the builders are not insects or moles—they’re burrowing crayfish.

Unlike their stream-dwelling cousins, terrestrial crayfish spend most of their lives underground in moist soil. They’re nocturnal, doing their digging at night, which is why the towers seem to appear out of nowhere by morning. Using their claws, they excavate soil from deep tunnels and stack the wet mud around the burrow entrance. The chimney helps regulate airflow and humidity inside, creating a cool, livable space several feet below the surface.

Crayfish prefer moist environments with soft soil and high groundwater. If they’re in your yard, you likely have damp conditions, good drainage, and a balanced ecosystem. Their burrows are usually harmless. In fact, the digging improves soil aeration and water penetration. Large numbers of burrows can create uneven patches, but for most homeowners, they’re more a curiosity than a problem.

To discourage them, improve drainage and reduce overly wet conditions. Gently flattening the chimneys can help, though they may rebuild elsewhere. Avoid harsh chemicals—they harm beneficial wildlife. While these mud towers may seem strange, they’re signs of a living, active ecosystem beneath your feet. Next time you spot one, you’ll know exactly who the tiny nighttime engineer was. Nature is constantly at work, even in the quiet corners of your own backyard.