For many kinds of flyfishing, insects are very important, as they are what we are trying to imitate to catch fish. This FAQ will explain the basics of entomology as it pertains to flyfishing. We avoid using the latin, scientific terms here so that the FAQ is easily readable. However, in time many flyfisherman learn the scientific terminology for much of what is discussed below. A few things to keep in mind.
Large insects are probably simply too vulnerable during low clear water.
Also, in tailwaters or spring creeks, where the water flow and temperature is more constant, the smaller insect species, especially midges, tend to dominate. Finally, after the growing stages, when an insect hatches from one stage to another, it usually drops in size. The insect is underwater and in some insect species this is a very important food stage for fish. Pupa - the second stage after hatching, but still immature. The insect is underwater still, and can be an important food source for fish.