There are many species of crawfish in Louisiana, but only a few in America's WETLAND. Our most common species burrow during the late summer, spend most of the fall and winter underground in water filled tunnels, then move to open water (anything from roadside ditches to swamps, ponds, bayous, and lakes.
First, are crawfish important in the grand scheme of things? Mai, yeah! They are a wonderful part of our cuisine, and they are thusly an important part of our economy. They provide many jobs (from catching and selling to processing to selling back to customers like us to serving in restaurants and shipping around the nation). What would the world be like with no boiled crawfish or etouffe? I wouldn't want to know.
What kind of crawfish do we have in America's WETLAND? We have two commercial species: Red Crawfish (Procambarus clarki) and White or River Crawfish (Procambarus acutus). Before you get confused, they both look red when cooked with good seasoning. The easiest way to tell them apart is that in the Red Crawfish, the pinchers are heavy and thick; the White Crawfish have at least one long and slender pincher. In general, Reds are found in swamps, bayous, and ditches, and Whites are more in large, deeper bodies of water such as lakes. However, they may be found living together. Almost any sack of crawfish will have mostly Reds and a few Whites.
Other than eating and selling, what is the value in crawfish in nature? We call crawfish detritivores. That is, they break down organic material like leaves and stems. All day long, they sit around munching on leaves. The benefit is that if we didn't have things like crawfish doing this, we would soon have leaves and other organic material stacked up 10 ft deep.
While they are munching on leaves, they are also consuming lots and lots of microbes (little microscopic organisms), and ingesting their protein. This is their main source of protein, so next time you eat crawfish tails, just say to your friend, "This is the best microbial protein I've ever eaten," because that is basically what you are eating - though it has been transformed into a crawfish (do you think if something eats a Louisianian, it thinks, "This is good crawfish protein"?).
What are crawfish chimneys? Crawfish chimneys are those "smokestack"-looking things that appear in field 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 characteristics of soil layers below the soil. As the crawfish burrows down, it brings up soil from different layers and deposits the pellets of mud in 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 and put on the surface. The next pellet is set beside the first. This continues, much like a brick layer putting bricks on one layer, 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 one and you will clearly see this neat system.
Why do they build chimneys? This is not completely known (no one has ever talked to a crawfish), but there are a couple of theories.
The crawfish has to dig its burrow in order to be able to submerge in water beneath the water table. As it does so, it has to do something with the mud. If it takes the mud outside the burrow and crosses the ground to dispose of it, the crawfish will be vulnerable to predators. To avoid that, they learned to build the chimney, thus never leaving the entrance of the burrow. If you ever approach a chimney and the crawfish is visible, you will see how quickly it can fall/scurry back down the tunnel.
Many animals are known to construct their burrows in such a fashion that they enhance the flow of air through the tunnels. It is known that the water in crawfish tunnels may get low on oxygen. It may be that the chimneys help air flow into the burrows so that oxygen can be absorbed in the water.
What happens to burrowed crawfish during droughts? One of their first responses is to plug their burrows with mud. This is especially true of horizontal burrows near the surface. As the water table drops, the animal moves further down (this is the same response they have to cold weather - they move down to warmer water levels).
How many crawfish per burrow system? One.