Fly Fishing Entomology is one of the many things in fly fishing that has been WAY over complicated. Fly fishing entomology really boils down to a 3rd grade science quiz. Don’t make it more complicated then it needs to be!
Though this is over simplified and we will not cover the various species in each category. Even so, you will be able to “match the hatch” by understanding and matching the common characteristics of each insect you see on the water to the flies in your box.
For practical purpose, fly size is rated from #2 (large fly) to #24 (small fly) in increments of 2…. 2,4,6, 8, 10 and so on…
There are a variety of different life stages and insects we try and replicate with artificial flies. Nymphs are subsurface insects & organisms that trout eat. Dry flies are used to replicate the mature stages of stream born insects or anything that floats and that trout might eat (grasshoppers, ants, etc).
Midges are the smallest and hardiest of the stream born insects. The hatch in a variety of water types, temperatures and are very common on tailwaters & best fished in winter & low/clear water conditions. #18-24.
Must Have Midge Nymphs:
Must Have Midge Adult Dry Flies:
Mayflies come in a variety of different sizes but the body structure remains consistent. Distinguishing marks of the nymphs are three tails and a streamlined body. The adults fly gracefully and look like a sailboat when sitting on the water. You will hear a variety of insect names tossed around such as Blue Wing Olives (BWO), Pale Morning Duns (PMD), Tricos, Drakes, Quills etc. These are all types of mayflies. #10-24
Must Have Mayfly Nymphs:
Must Have Mayfly Dry Fly:
Caddis are a common stream born insect we see in the summer months once water temps hit 50 degrees. The nymphs will often develop in a casing much like a caterpillar and swim to the surface (emerger) once they have developed and water temps are correct. The adults look like moths in flight and when resting have a tent shaped wing. #12-20.
Caddis Nymphs (larva)
Must Have Caddis Nymphs:
Must Have Caddis Dries:
Stoneflies are distinguished in the nymph stage by two tails and two antennas. They can range from size 4 (salmon fly) all the way to size 20 (yellow sally). Unlike other insects mentioned, stoneflies crawl out of the river and break out of the exoskeleton which you will see along the bank during stonefly hatches. The adults have two sets of wings.
Must Have Stonefly Nymph
Must Have Stonefly Dry
Other Stuff Trout Eat
Aside from the hatches mentioned, there are other food sources that either live in the river or fall in the river but don’t grow wings and fly such as…
- WormsleechesCrawdadsminnowsfreshwater shrimp
Must haves flies in the “other stuff” Category…
San Juan Worms, Barr’s Slumpbuster, Buggers, Amy’s Ant