J ust because the bugs are flying, you don't necessarily want a can of spray stuff to kill them. For fly fishers, flying bugs are a good sign.
Bugs sitting on the water are terrific.
Bugs crawling out of the water are great. Even those still clinging to the underside of rocks in the stream can give you a good clue. Birds swooping over a stream are eating bugs too. Most of the insects trout eat don't have any working mouth parts. Put simply, they can't bite.