There’s a population of fly fishers that love to fish during an insect hatch. It’s sort of like piecing together a puzzle. Some technical minded folks really light up when given the chance to analyze a hatch. The fish are up and feeding on something, birds are swooping low to the water, mice hit the shoreline vegetation searching for the insects that make it to land(Yes, I’ve seen this. I was surrounded by a whole colony once while they were on a feeding frenzy.)
You scan the air, the water, the bank side vegetation in search of the insect that is causing all the commotion. You might even have an insect net or use your hat to catch one for a closer look. Now you know what they are feeding on, that is unless it is a double or triple hatch. Then you have your work cut out for you.
If your dealing with a single hatch then you can move onto figuring out what stage of the emergence the fish are feeding on. Maybe a nymph or pupa as it makes it’s way to the surface or an emerger in the surface film. Could be a dun on the surface or an insect that has come back to the water to deposit eggs. What stage of the emergence are the fish feeding on?. Could be different stages depending where the fish are feeding in the river.
You have a fish picked out of the bunch. Do this because it is easier to catch an individual fish than it is to throw a fly in the area and hope one takes it. What’s that fish doing? Watch how often it rises to the surface. Time your cast when you think the fish is ready to eat again. Is it moving around an area or holding in one spot? You may even find them focused on feeding to one side or the other. Did the fish jump out of the water to get egg layers or insects flying across the surface? Did the fishes head come out of the water to take an adult insect floating on the surface? Did the fish only push up a little water or create just a dimple as it sips a fly from the surface film or just below it? You may even see fish feeding mid depth or near the bottom as the insects make their way to the surface.
If you can figure this all out you may be able to fool a trout into biting your fly. That is if you present it the way they want it. Now you may have to tweak your fly, equipment, or your cast to satisfy. Sometimes you only get one shot and the fish is spooked and down. Either you wait or move on to another fish, possibly a different area of the stream.
I’ve only described part of the process of fishing a hatch so you can imagine the possibilities and the challenge. Sometimes is can be stupidly simple to catch fish during a hatch and other times even Einstein would pull his hair out in frustration after a pea brained fish got the better of him.
Late May and early June trout streams are host to a smorgasbord of insect hatches for those that live for this stuff. Good luck, you may need it.