Big trout hunt for big bites...
Crayfish, Crawfish, Crawdads are common prey for trout, bass, perch and many others. These crawdad fly patterns are effective in rivers, streams, ponds, and lakes.
Crayfish live in the rocks found on the bottom of the river, eating plants, fish and insects. Given a choice, crayfish are nocturnal, but will be found at any time of the day.
The best way to fish a crawdad pattern in moving water is under an indicator. That allows a good drift, and keeps the fly at the proper depth. Crayfish vary in color from dark olive to brown, and in size as well.
Crawfish, crayfish, and crawdads are the same animal. Which term you use may depend much on where you live.