A sow bug is the 'rolly-polly' that you find behind old lumber in your garage. You know, you touch them and they roll up into a little ball. I've never tied or ever seen a sow bug fly (other than in fly catalogs) but I can't imagine that they'd be any different than a gray scud.
A sow bug (other than the roly poly kind) is another imitation of a scud or another similiar freshwater crustracean...there is a certain pattern i fish which is a local favorite on the Miracle Mile (first tied by an older gentleman whom lives in Lafayette) its tied anywhere from size 18-12 and is pretty much a staple on that section of the north platte...although not many people tend to fish this color. i myself have never seen a tan scud in the water---mostly just orange or amber (after they are dead) or a green or gray olive color. however this is one fly i wont fish the North Platte without, ive caught countless fish on this fly in a size 14 when nothing else worked. its a simple fly to tie also, just brown thread, gold wire, and tan dubbing...picked out so its like a big fluffball. i tie it on a scud hook or a straight shank 2x wire hook....with enough head cement they last all day.
thanks for the info and photos. i suspected it to be in the pill bug, potato bug (depending upon what you call them) family. i had a few tied for me for specific use on the mile. they look very similar to what you show/tie. the guy that tied them for me was from two guys fly shop. i got them for a trip to the mile last november.
The flies i think you are looking at are a foam back emerger i tied for a guy going to the Green...he had me tie 12 dozen, those are just leftovers ive never really fished too much. he liked them though, hence having me tie so many. the ones next to them are just variations of the Hurricane midge alot of guys fish on Grey Reef...red seems to be a popular color. All the flies in that box are for the North Platte, although i usually end up fishing the amber scuds, red tube midge, and the sow bug mostly on that river. The guy whom tied you the ones at Two Guys use the sow bug alot, (origionally tied by a guy named Honny, a local) I know this because i used to work at Two Guys and still fill in on occasion and we sell a lot of those patterns.