I was amazed yesterday at the prolific handiwork of Burrowing Crayfish in the Voice of America (VOA) MetroPark in Butler County located in southwest Ohio. Hundreds of their unusual looking mud structures were rising from the soil in turfgrass and naturalized areas. The structures are most often described as mud "chimneys" because of their columnar shape and large, round hole in the center. However, I've always thought they look more like tiny volcanoes built by mud erupting from the crater-like holes. Either way, no other animal produces such unique mud structures in Ohio.
Burrowing crayfish in Ohio belong to one of two genera in the family Cambaridae: Cambarus and Fallicambarus. These land-lobsters are sometimes referred to as Terrestrial Crayfish owing to their lack of a direct connection to bodies of water. However, just like their aquatic cousins, these crayfish use gills to extract oxygen from water. Unlike their water-soaked cousins, burrowing crayfish spend most of their lives on land.
Because they are aquatic organisms, burrowing crayfish must dig their burrows down to ground water so they have a ready source of oxygen. This connection to a high water table explains why most burrowing activity occurs in poorly drained soils near streams, ponds, or around shallow ditches. Indeed, the mud chimneys I observed yesterday in the VOA MetroPark were all in close proximity to a large lake.
The crayfish throw soft mud up around their exit holes as they excavate the soil. If you look closely, you may see scrapes and groves made by its chelae (claws) in the fresh mud. These chimney-like structures may eventually tower 3 - 8" above the soil surface. The omnivorous crayfish leave their burrows at night in search of plant and animal food, living or dead. You may find them several feet from their subterranean abodes if you use a flashlight and practice a little stealth.
Unfortunately, the mud chimneys can present a real hazard to mowing. Hitting a sun dried brick-hard crayfish chimney with a mower dulls mower blades, blasts out clay-shrapnel, and sends up huge clouds of dust … often accompanied by a stream of expletives. This makes burrowing crayfish a serious nuisance pest for turfgrass managers.
However, there is little that can be done to directly control these terrestrial "mud bugs." DO NOT pour toxic materials down the holes to kill the crayfish because the burrows extend down to ground water which could become contaminated. Successful management of these sometimes bothersome crustaceans generally focuses on physically reducing the high profile of the chimneys, patience, and habitat modification.
Physical reduction provides a temporary reprieve and includes stomping or raking smooth the chimneys prior to mowing. This does not kill the crayfish deep in their burrows, so chimneys will eventually reform and must be dealt with before the next mowing. Patience focuses on recognizing that most of the crayfish's excavation activity occurs early in the season, and will subside as the season progresses. Habitat modification focuses on improving water drainage to lower the water table. This may involve lowering nearby drainage ditches.
Despite their sometimes nuisance status, research has shown that burrowing crayfish are important members of certain terrestrial ecosystems. Their burrows help with drainage by providing a direct pathway for water to flow into the ground. Their foraging helps to recycle nutrients. They move oxygen and nutrients deep into the soil profile. Abandoned crayfish burrows provide homes or protective cover to a range of other invertebrates as well as few vertebrates. And, they are simply fascinating creatures!