Fly Life Cycle

One of my blog followers ask for pictures of common mayflies. Before I post some of the popular flies mentioned in previous posts, I decided to start with the life cycle of a fly…so as fly fisherman, we can understand what the trout are feeding on in various stages.

Simply put, the stages are: egg, nymph, emerger, dun, spinner, adult mayfly

Spinners: Mature females lay their eggs on the water producing larvae.

Nymphs: The larvae turn into nymphs – when trout are not rising they are likely feeding on nymphs.

Emergers: Nymphs migrate or emerge to the surface, therefore called emergers.

Duns: When the nymph molts (produce wings) the bug is now called a dun. The dun sits on the surface in order to dry its wings and then becomes an adult mayfly.

Adult mayflies then become spinners…the males and females mate…. the females lay their eggs on the surface and the cycle starts all over again.

The types of flies are cyclical, so it is now up to us fly fisherman to focus on the type of fly, size, shape and color. Since, I mentioned on previous posts, that I am a dry fly fisherman, I focus on the duns and adult mayfly/spinner stages. Stay tuned for the more popular ones on the Pennsylvania trout streams.

2 comments on “Fly Life Cycle

  1. Bass Man says:

    Good stuff “Troutscout” I have always wondered about
    the different stages, just never had the time to look it up.
    I was wondering though, how long does the life cycle of
    a mayfly last? In other words from the egg stage to an adult
    mayfly….how long does this take to happen and does water
    temperatures have anything to do with the process?
    Thanks for the information.

  2. Good question Bassman! The nymph stage can last from 2 months or longer -up to 2 years. The stage after emerging to dun and the the adult mayfly is short. The average adult only last 3 days. As I said before, the mayflies are cyclical and a specific hatch repeats every 12 months. So a Brown Drake which hatches on a specific stream in March will normally occur again in March the following year. Water temperature is also a factor. Stream temperature in the 50s is ideal to start the emerging stage. When water temperature exceed 70 degrees, trout become lethargic and will go in shock if hooked and can die if played too long. Good flyfisherman should be aware of the temperature and should refrain from fishing during these warm stream temperatures. That is why spring creeks are always good because stream temperatures stay consistently cool. Freestone streams with “tailwater” (dam controlled) normally stay cool as well. Freestone mountain streams are not “tailwater” but are typically well shaded; therefore, have desirable temperatures under 70 degrees even during the hot summer months.

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