It looks like I’ll be spending around ten days in Missouri when the Yellowstone is in runoff in mid-May. I grew up there, but seldom fly fished for anything but trout. This time I plan to fish for smallmouth, carp, and gar. I’m good for flies on the latter two species, but for smallmouth I think I’d have a tendency to tie way too many different patterns and not enough of each one. So any suggestions for must have miss bugs I want to tie at least a dozen of for Ozarks smallmouth in mid-May? I expect to river/stream fish only: Meramec, Big, Castor, Bryant Creek, Big Piney, and St. Francis are the most likely.
crawdads and streamers. the specifics are up to you and not that important.
My too favorite patterns for smallmouth subsurface are the Golden Retriever (fished dead-drift as a nymph), and a small clouser tied with gold dumbell eyes and white/red/white bucktail…or yellow/red/yellow bucktail. I tie them on #6 Mustad C67 with red thread.
On the top I like a large Foam Butt Caddis, in Dun with black/tan ruber legs or in Olive with Chartruese/black legs. But I have caught smallmouth on both coasts with a Smallish bass/blugill popper #6-8 as well…usually in yellow or black.
Ralph
I’ve been hearing about a fly called a “56er” that is an immature crawdad imitation that’s supposed to work well down that way.
NJTroutbum: what color on the Golden Retriever? That bug looks like money, and certainly a quick tie…
Herefishy: Here’s a vid for the 56er. It looks like a killer soft-shell crayfish and I’m going to tie some for carping out here. http://www.youtube.com/watch?v=T_FyMmjPQsY
Terry and Roxanne Wilson live in southwestern Missouri. They are both avid warmwater fly fishers/tyers, and they have written the definitive guide to fly fishing for smallmouth:
Smallmouth Bass Fly Fishing: A Practical Guide
The book contains a number of proven smallmouth patterns, including “local” Missouri patterns, as well as many proven patterns from Federation of Fly Fisher tyers from across the US, including one of mine!
If you pick up a copy of this inexpensive paperback book, I’m sure that you?ll enjoy it and that it will help you to greatly enhance your trip.
Bowfin47
PS
They have also written two other great books on fly fishing for bream and largemouth bass that every warmwater flyfisher/tyer should invest in:
I’ll add a little bit to the list:
On Missouri streams, I’ve done well with streamers…and sometimes have slayed (slew?) them with black stone fly nymphs. Maybe they look close enough to helgramites.
From the rivers you mentioned, you should do well. I would also look into the Jack’s Fork River, the lower Current River, and the Little Piney.
I’ve spent all of my life in Missouri and I’d be glad to give you any help I can. In 2010, I was planning a trip to Yellowstone and looked for tips and ideas and Walt, you were most helpful to me while I was planning my trip. PM me for any specifics or questions you might have. 
Brian
LFC…I tie it as the original with red thread, Peach Estaz, with a tan marabou tail, and also in a rootbeer version (rootbeer estaz and brown marabou tail). I have not fished smallies with the white version, but hear that it does well also. I deaddrift the original gold version…but fish the rootbeer as a streamer.
Ralph
This fly in olive has been a good smallmouth fly for me on the Elk River in SW Missouri.
http://www.warmwaterflytyer.com/corner.asp?page=9
Steve