Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
There is an iron bridge there that stays warm after dark and it's a good place to lay and watch flying squirrels soar across the river, backlit by the sky.
I guess I'm trying to say that you have to define what you mean by important. Except perhaps in some localized areas, they don't offer much in the way of drift, though.
it appears that Corydalus cornutus is the accepted scientific name of the very common large megalopteran most of us know as hellgrammites or go-devils
By the way, I highly recommend the Merritt and Cummins book (now in a newer edition)