Article supplied by Buggy Joe Boggs
Experts divide crayfish "land-lobsters" into three general categories: Primary, Secondary, and Tertiary, based on the crayfish's life style. However, one size does not fit all; some crayfish don't fit neatly into just one of the three categories.
All crayfish are capable of burrowing; even those that live in streams (Tertiary). However, these crayfish only produce rudimentary burrows such as a groove beneath rocks to accommodate a hideout. Secondary burrowers produce more structured excavations, often in stream banks. But their burrows usually involve just a simple single-chambered tunnel from which the crayfish scuttle forth to take a swim.
Primary burrowers are the true excavators. Their burrows may include multiple chambers and their tunnels often extend deep into the soil far from streams. Of course, they must reach groundwater because all crayfish breathe with gills. This is why we usually find their burrows in poorly drained soil such as in or near drainage ditches.
The life-style of primary burrowers is supported by a number of evolutionary adaptions. Their claws (singular = chela; plural = chelae) are modified for digging. Their abdomens are often smaller than their more aquatic cousins because they don't need powerful swimming muscles. They have bigger gills to support sauntering about on land at night in search of food. The omnivorous crayfish will chow down on both 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.
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 in the fresh mud. These chimney-like structures may eventually tower 3 - 8" above the soil surface.