Crawfish are not insects, but freshwater crustaceans resembling small lobsters.  Crawfish (also known as crawdads, mudbugs, crayfish) are not harmful to turfgrass, but can become numerous in poorly drained soil. They build unsightly tubes that may reach several inches in height.   There are no registered or recommended pesticides for  crawfish control. Improving drainage may reduce earthworm populations and crawfish activity.