Crayfish (also known as crawfish, mudbugs, crawdads) can live near or far away from water bodies. They survive by creating burrows in the ground. While they are excavating their burrow, they carry pellets of mud to the surface and place them around the opening. Eventually, the dirt they remove grows higher and higher, almost resembling a chimney. These mounds of dirt they create can be unsightly, and the burrows they dig can damage lawns, shrubs and ornamental plants.
What Not To Use
Aside from the fact that there is no real way to completely eliminate crayfish, you really wouldn't want to because they are very beneficial to other wildlife as a food source. Any poison or pesticide that might be lethal to crayfish can not legally be applied to the ground because it would contaminate ground water. And because other wildlife eat crayfish, there's a strong chance they too would be poisoned after ingesting the crayfish. There are commercially-available repellent products that are safe for the environment that you can use to discourage crayfish.
Crayfish burrows typically have several exits, so it's safe to knock down the mounds that appear in your yard. Apply vole/mole deterrent over the flattened mound to discourage the construction of a new mound. See the section below entitled Damage To Trees and Shrubs for another alternative approach.
You can purchase mole repellent or make your own DIY homemade crayfish repellent using our recipe. Castor oil is the primary ingredient in most commercially available mole and vole repellents.
Damage To Trees and Shrubs
Sometimes crayfish damage extends to shrubs, bushes, and small trees. In our experience, after examining the roots of unhealthy plants and shrubs, we observed that exit holes for crayfish tunnels were located directly around the base of the plants, and their roots were exposed along the length of these tunnels. The plants weren't dead, but they also weren't thriving. The soil around the exit holes also appeared very dry. The plants' root system was compromised and they weren't getting enough water or nutrients (or both).
Restoring the structure of the soil around the shrubs and trees was necessary. Completely filling the crayfish tunnel (which can be several feet deep) wasn't an option. Digging up and turning the soil around the plants' base so that the roots would once again be in direct contact with soil was the best approach. If there are a lot of tunnels that need to be addressed, we found that using a pressure washer was the quickest way to complete the task. A garden house might work if your soil doesn't contain a lot of clay or rock.
Aim the pressure washer directly at the tunnel opening and disrupt the soil so that it begins to collapse into the hole. Avoid applying the spray towards any roots; this could strip them or damage them further. Continue working up the soil around the tree or shrub until the soil begins to puddle heavily. Let the soil drain. Then repeat if you see any areas that have settled lower than others, which indicates that some of the tunnels may still be intact.
We found that the deeper we went, the less likely that crayfish holes would reappear. Perhaps because of the soil texture, they weren't able to create intact tunnels in soft soil. Within two weeks, the shrubs and trees were beginning to show new growth.
Based on those results, we also treated the mounds located within the yard. No new mounds re-appeared in the locations where the soil was disrupted. New ones came up elsewhere, but we continued to treat those as they appeared. While this may all be antecdotal (lacking research to show it will for everyone), this worked for us.
Your neighbors may look at you oddly while you're outside pressure-washing crayfish tunnels, but you'll have the satisfaction of knowing you're saving your shrubs/trees and making life just a little more difficult for the crayfish.