Bass, I learned a simple crawfish fly that works from the guys at Wapsi. They were tying these at the Sowbug Roundup 2 or 3 years ago.
Hook: 3X or 4X long streamer hook size 8
Weight: lead dumb-bell eyes
Claws: short section of a crawdad orange pine squirrel strip
Antenna: rubber leg material
Body: brown pine squirrel strip wound up the hook shank

After attaching the dumb-bell eyes, wrap the thread back to the bend. Tie in the rubber leg material extending past the back of the hook. Wrap a small ball of dubbing to separate the claws and then tie in the claws. Tie in the brown pine-squirrel strip and wrap it on the hook shank, stroking the fur back as you make each turn.
When you get to the front take a couple of wraps around the lead eyes and tie off.
That's it. Simple, but the smallmouth bass around here love it.
Steve

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"If there are no dogs in Heaven, then when I die I want to go where they went"-Will Rogers