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.
These images are from Wisconsin's Namekagon river. It was a wonderful start to the season. It's also basically all that I did over my spring from college. When I wasn't on the river, I was preparing for the next trip. Stoneflies were plentiful on the surface a couple of days (in size 12 and 14) we managed to rise a few on dries. The other action came on small nymphs.
One can learn a lot this time of year, given some decent weather. And for me, all it takes is a 40 degree day and one trout to relapse into the frenzy of a new season.