A variety of backyard pests leave dirt piles as their "calling card," but only burrowing crayfish build chimney-shaped mounds of mud. Crayfish are traditionally water-bound, but when species such as burrowing and grassland crayfish outgrow their habitat, they relocate to grassy regions such as residential backyards.
The more than 500 species of crayfish originate from one of two families: astacoideae and parastacoideae. Most of the U.S. varieties fall under genus Camberus, a 10-leg variety which resembles a crab. Home, Yard & Garden Newsletter, a publication of the University of Illinois Extension, describes crayfish as nocturnal, predatory crustaceans that feed on a wide range of insects and plant life. They breathe with gills and, despite a grassy habitat, burrow deep in the ground in search of water. Some crayfish burrows are nearly 6 feet deep.
Chimney-shaped mud mounds serve three functions for crayfish. First, they protect them against predators such as raccoons, birds, large fish, turtles, frogs and snakes. Second, female crayfish use the burrow to raise their young, especially during dry spells. And finally, the male and female crayfish use the burrow during molting periods. While burrows vary from inches to feet in depth, the opening typically measures from 1/4 to 2 inches in diameter and mound height ranges from 2 to 4 inches.
Crayfish mud mounds, though interesting, can dull lawnmower blades or burn out lawnmower engines. The crayfish's burrowing habits also compromise bank integrity along waterways, weaken earthen dams and create leaks in reservoirs. Because crayfish are omnivores and eat plants, they are responsible for damage to gardens, lawns and crops.
Killing crayfish with pesticides can harm other wildlife that share common habitats, and there is no federally approved pesticide for use against crayfish, according to WalterReeves.com. The best approach is a biological one. Virginia Cooperative Extension reports that the introduction of natural crayfish predators offers promising results. Ponds with trout, bass and catfish have reduced crayfish numbers. On land, many amphibians, reptiles and small animals such as raccoons are natural crayfish predators.
Trapping crayfish is an effective population-control method. Crayfish are attracted to fresh fish or meat. Any wire-mesh trap with holes smaller than 1/2 inch can be dropped in local ponds, in backyards or on banks and embankments of streams and ponds. Virginia Cooperative Extension recommends setting traps in late afternoon when temperatures peak and leaving them out overnight. To prevent crayfish from eating all the bait, wrap it in cheesecloth or some mesh fabric.