After all that rain we got last week, it isn't surprising that most of the inquiries I received would be about crawfish and their "chimneys." There are over 500 species of crawfish scuttling around the world, with around 100 of them enjoying life here in Mississippi. For the most part, they look a great deal alike no matter where they're found.
There are a few large species (a black one in Texas and a blue one in Australia grow to over 30 centimeters), but most crawfish are around 7 centimeters long. Like all crustaceans, they have 10 legs. The front pair is enlarged into pincers that they use for defense, feeding and mating. Crawfish feed on everything from algae to small fish, insects, snails, tadpoles and worms and other, smaller crawfish -- pretty much anything smaller than them that can't get out of the way fast enough.
Crawfish tend to be found in and around fresh water. Fresh water usually means a stream, but if the water table is high enough, they will readily colonize your lawn. If they're in your yard, you probably know it all ready. The crawfish chimneys are a dead giveaway. These knobby mud columns are a crawfish's castle and it's where they spend the daylight hours floating deep inside the water-filled tube. It's these chimneys that are the major cause of concern for homeowners. The tubes, after baking in the sun for a few days, become as hard as a teenager's head and, besides being unsightly, can cause significant damage to your lawn mower. At the very least, they'll quickly dull the blade.
Mama Nature does a good job in keeping crawfish populations under control. Crawfish are eaten by alligators, birds, cats, fish, raccoons, turtles and even squirrels.
For most homeowners with these crustaceans infesting their yard, even one chimney poking up through the centipede lawn is going to be too much to tolerate. If you want to get rid of crawfish, there are only a few things you can do, and most are limited and temporary. First, you can go out in the evening and hand pick the crawfish as they wander around. You can set out traps baited with meat, fish or chicken.
If the chimneys aren't too deep, you can poke a sharp stick into the column and, with any luck, squish them. The most effective (but costly) way to eliminate crawfish is to drain the area they've colonized, but if you live in a low, wet area and the water table remains high, the problem will return. If you have a large lawn, you might consider letting the spot that the crawfish like revert to a wetland.
There are no pesticides labeled for crawfish control, but there are a few "old time" poisons that people have used successfully over the years. Poisoning large areas to kill crawfish is problematic at best and can contaminate the water table. However, you can treat individual burrows. One method involves dropping two or three pellets of lye (sodium hydroxide) into each tube. Another requires pouring concentrated vinegar down the column then pressing the opening of the chimney closed with your foot. The mixture increases the acidity. It should kill the crawfish within a few hours. Acidification, however, is determined by the amount of water in the column, something you'll have no way of determining.
If you are successful in eliminating the crawfish from your property, you may want to consider erecting a solid wood, brick or stone fence to block or, at least reduce, the migration of crawfish into your yard. Keeping them out may be your only option. Given time, they will recolonize any suitable habitat and you'll have to begin the process all over again.
Tim Lockley, a specialist in entomology, is retired from a 30-year career as a research scientist for the U.S. Department of Agriculture. For answers to individual questions, please send a stamped, self-addressed envelope to Tim Lockley, c/o Sun Herald, P.O. Box 4567, Biloxi MS 39535.