By Bob Thomas
There are many species of crawfish in Louisiana. Some are rather drab, while others are ornately colored with blues, reds, yellows, and greens.
Only a few species occur in our coastal wetlands; all are restricted to freshwater.
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.
Are crawfish important in the grand scheme of things? Mais, yeah! They are a wonderful part of our cuisine, and thus are an important part of our economy. They provide many jobs — from catching and selling to processing to being served in restaurants and shipped around the nation. What would the world be like with no boiled crawfish or étouffée? I wouldn’t want to know!
What is the value of crawfish in nature? Well, for one, they burrow much of the year and aerate soils that might otherwise have depleted oxygen levels.
Crawfish are detritivores. That is, they break down organic material such as leaves and other plant parts. 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 over our heads.
They also eat living plants and such creatures as worms and insects.
The Chimneys
Now, let’s look at what crawfish chimneys are. Crawfish chimneys look a little like smokestacks. They appear in ditches, fields and yards each spring. Everywhere you see one, there’s a crawfish living in a burrow underneath. Their tunnels may extend down into the earth 3 feet or more. Sometimes it’s a matter of a single burrow going straight down, but more often there’s a main tunnel with a couple of side tunnels, each with a room at the end. They are normally full of water.
A crawfish may make two crawfish chimneys at one time.
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 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? They use their legs and mouth parts to dig up mud and make it into a little ball or pellet. Each pellet is taken to the surface and placed on top of the chimney. The next pellet is set beside the first one. This process continues. It’s a bit like a brick layer putting bricks on a surface, then making another layer and so on 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 system at work.
Why do crawfish 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, the crawfish have learned to build the chimney without 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 or run back down the tunnel.
When There’s A Drought
What happens to burrowed crawfish during droughts? Crawfish routinely plug the openings of their burrows with mud during dry periods. This is especially true of horizontal burrows near the surface, since the crawfish can’t move deeper to remain wet. As the water table drops in more vertical burrows, the animal moves further down. This is similar to the response crawfish have to cold weather. They move down to warmer water levels.
As was noted above, over time, oxygen can be depleted in the water filling a burrow. When this happens, the crawfish may position itself just above the water, thus keeping its gills wet and absorbing oxygen from the air in the burrow.
Crawfish Eggs
Next, where do crawfish lay their eggs? They lay their eggs in their burrow and keep them attached to little appendages under the tail called swimmerets or pleopods. As long as oxygen levels in the burrow water are high, the adult keeps the eggs under water. As the oxygen drops, the adult keeps the eggs moist and also gets them out of the water, thus allowing them to absorb oxygen from the air.
The eggs usually hatch in the burrows; they then begin to grow. Since there is a restricted amount of food available in the burrow, the youngsters consume infertile eggs and the carcasses of deceased siblings. And in fact, if it is necessary, they will kill one another in order to survive.
Once the rains begin and pools form on the surface, the crawfish move out of their burrows and into the environment on the surface. The babies usually stay with their mom for a short period, but eventually get on with life and disperse throughout the realm.
How Many Crawfish Are There?
How many crawfish can be found in each burrow system? Usually there is just one. However, there may sometimes be a male and female present.
Once the eggs are laid, the male typically stays near the entrance and the female remains deeper in the burrow.
— Originally published in the Louisiana Levant Magazine, June 21, 2007. Courtesy of the Loyola Center For Environmental Communication.
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