NEW ORLEANS -- The little hollow mudball towers called crawfish castles are fine in the swamp but not so great in your yard.
"They're hard on lawnmowers and mower blades and that kind of thing," said Lee Townsend, an extension entomologist at the University of Kentucky in Lexington. If the soil holds much clay, "they bake and harden like a brick," he said.
Greg Lutz, a crawfish specialist at the LSU AgCenter, said he's been getting calls from people who want to get crawfish out of their yards.
He usually gets about 30 to 50 such calls a year and this year has run about average, he said in an email.
Many are in early summer when mother crawfish have carried their young to the nearest ditch, stream or lake, then returned to their burrows to clean out and enlarge them. Young crawfish may be digging their first burrows, Lutz said.
No approved pesticides
There are a couple of big problems clearing out crawfish. For one, Lutz said, the Environmental Protection Agency hasn't approved any pesticides for crawfish.
States can get the occasional exception. For instance, in 2010, Wisconsin got permission to use a pesticide to control red swamp crayfish at three specific spots.
Putting pesticides into the burrows can contaminate groundwater, Lutz said.
"Using pesticides in burrows is not only a bad idea, it's also illegal. And putting bleach down in the burrow is often ineffective," he said.
A fact sheet by Townsend, recommending two possible treatments, has been cited in a number of Internet discussions of lawn crawfish. But that fact sheet, created in the 1960s, has long since been removed from the extension service website as outdated, Townsend said in a phone interview.
There aren't a lot of choices, he said.
Some species protected
Another problem is the crawfish might be protected.
Of more than 350 crawfish species in the United States, about 65 are endangered, threatened or listed as species of special concern by the states in which they live, and 48 percent are in need of protection, according to Virginia Cooperative Extension at Virginia Tech.
Although Louisiana raises and catches more than 50,000 tons of crawfish a year to eat, the 39 species found in the state include more than a dozen considered rare or even critically imperiled by the state Department of Wildlife and Fisheries.
Flush 'em out
If there are only a few holes, they can be filled with water to flush out the inhabitants, said Robert Romaire, another LSU AgCenter crawfish expert.
For common species, Lutz said, one way to kill them is pouring about a tablespoonful of lye into each hole. Lye doesn't pollute as it migrates into the soil, he said, but is caustic: the user must protect skin and eyes.
He emphasized in an email he can speak only for Louisiana because rules vary widely from state to state.
The North Carolina Extension Service suggests raking the mounds smooth from time to time, creating drainage to leave surface soil less soggy, or just appreciating crawfish as one would an "interesting bird or turtle."
Crawfish appreciation is the tack taken by writer and artist Ursula Vernon of Pittsboro, N.C., after a burrow she thought might house some sort of rodent turned out to be home to a crustacean.
"Once I finished running around like a chicken with its head cut off, I thought it was kind of cool," she said.