Muskrat--Soft grayish fur ideal for Shenk's Cress Bug.
Fox Squirrel--Tan fur for red fox nymph thorax.
Beaver--Very fine brownish fur for shrimp and small drys.
Red Fox--Gray/tan fur (long) for large nymphs.
Mink--Silky gray/brown with long brown guard hairs, good for many soft hackles.