As cooler weather and colder water set in to stay, most local fly fishers make the seasonal switch to nothing but tiny flies. This is logical...the bugs that are out and getting eaten are all midges and the smaller of the Blue Wing Olive mayflies. I will often still use some bigger stuff, especially when searching a creek I haven't been on for awhile. I like to use a bigger, bushier hair wing dry (such as a Stimulator or Clown Shoe) with a midge pupa imitation (#20 Zebra Midge or Poison Tung) hanging off the hook bend about 12 to 18 inches. Most of the trout willingly take the subsurface midge, but every now and again one of the big boys (relative term, of course) will inhale the dry!
I like this type of fishing because the big dry is always easy to spot on the water and is always nicer to cast than a strike indicator.