hi jen,
Many times with overlapping hatches....you'll have mayflies, caddis,
and anything else.....which often is the little "dessert" that the
trout ARE feeding on, the bugs that you have to really get close
to(scoop up) to see/identify...thus imitate.
What really helps is to learn what specific hatches populate that
particular streambed..and at that time of the season... Also, the
particular rise-forms will often give a hint as to just what the fish
are feeding on. Splashy= high-riding caddis or mayfly
duns....sub-surface bulges/rings= emerging mayfly nymphs/spent mayfly
spinners/caddis pupae....(for example). Trout will always be looking
for food stuck in the surface film...so you don't always have to come
up with an exact imitation...getting a fly at the level where they're
feeding at will always get action, it may take time, but it will get
interest...