The shellback is squirrel tail same as the tail. Very simple tie with only 3 ingredients: squirrel (or other long hair for back and tail), dubbing (your choice) or chenille, and a grizzly hackle or two. Add enough weight to keep it near the bottom and presto! Done!
Del Canty first tied it in the early 1970's based on his theory that trout in waters with lots of scuds (freshwater shrimp) get so focused on the general shape and image of the shrimp, that they'll even eat one that's far bigger than any live scud. He fished from a float tube at night and used to pull in some real monsters like this record rainbow (on the shrimp):
The fly was a local secret on Flaming Gorge in the '70's and early '80's until the rainbows and browns declined and lake trout took over. Being such a secret, the fly never gained much press aside from some mentions in magazines that never showed it or detailed its construction.
Del's friend, Joe Butler had a Grizzly Shrimp (#4) tied on one evening in April, 1978 when he was walking the shoreline near the dam and cast towards where he saw a big fish porpoising and chasing chubs. The result was his record brown that was on the books for over 20 years:
He theorized that the Grizzly Shrimp mimicked a crawfish and Flaming Gorge does have plenty of those. For whatever reason, big trout seem to go for this fly in Stillwater.
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