Ive lived less than a mile from the creek my whole life and never thought of eating a crawdad from there. Ive kept a few as pets when I was a kid but...I guess you could snap one open and see if little worms go flying everywhere....
They actually are pretty good if you can get any size to them. They are mini Lobster. Drop them in boiling water, do't worry about the screaming it won't last long. Break off the tail, pull out the poop chute, dip them in melted butter with a little garlic salt added then pop them in your mouth, YUM! I can only eat 50 or so!