Midges hatch all year long and usually emerge during the nicest part of the day, they experience a complete metamorphosis egg, larva, pupa and adult. Two, three or more generations occur per year.
The life cycle takes from 2 to 4 weeks or as long as a year.
The farther north you go the larger they get.
Dr Ernest Schwiebert told me the most important thing about the presence of adult midges on the surface film is that there are pupa under the film. Most anglers agree the pupal stage is most important to the angler.
Suspect midge pupae whenever trout are rising but you can't see what they are taking