Crawfish chimney

Description:

This is the sand and mud excavated by the resident crawfish as she built her burrow. It's situated next to a deep roadside ditch. She's underground laying her eggs, or hatching them, or tending to her brood. There are many kinds of crawfish ... no way to tell which kind built this chimney.

Notes:

Also called crayfish, crawdads or mud bugs. Considered a delicacy all along the U.S. Gulf Coast.

From the Loyola Center for Environmental Education:

Crawfish chimneys are those “smokestack”-looking things that appear in ditches, fields, and our yards each spring. Everywhere you see one (sometimes a crawfish will make two), there is a crawfish living in a burrow underneath. Their tunnels may extend down into the earth 3 ft or more, sometimes being a single burrow going straight down, but more often being a main tunnel with a couple of side tunnels, each with a room at the end. They are normally full of water.

Sometimes one sees that the color and texture of the chimney mud is different at different levels of the chimney. This is a sign that there are different types of soil layers below the surface. As the crawfish burrows down, it brings up soil from different layers and deposits the pellets of mud at the top of the chimney.

How do they make them? No, they don’t have little backhoes or dredges. They actually use their legs and mouth parts to dig up mud and make it into a little ball called a pellet. Each pellet is taken to the surface (the crawfish moves through the burrow looking like a fullback carrying a football) and placed on top of the existing chimney. The next pellet is set beside the first. This continues, much like a brick layer putting bricks on a surface, then making another layer, etc. until a building is totally bricked. The crawfish makes the chimney out of many, many pellets of mud. Take a close look the next time you see a chimney and you will clearly see this neat system.

Why do they build chimneys? This is not completely known, but there are a couple of theories.

The crawfish has to dig its burrow. As it does so, it has to do something with the mud. If it took the mud outside the burrow and crossed the ground to dispose of it, it would be vulnerable to predators. To avoid that, they learned to build the chimney, thus never leaving the entrance to the burrow. If you ever approach a chimney and the crawfish is visible, you will see how quickly it can fall/run back down the tunnel.