Weather  MDC

Mayfly Life Cycle

Life Cycle Single most important of the insects
Over 125 species important to the fly fisherman in the United States. Only about 15 species important on most streams
Two tail wings, two or three tails and usually two hind wings. They look like little sail boats on the water and are the only trout insect with upright wings.
As a general rule, early season mayflies tend to be darker: gray wings with brown or olive bodies (March � May).
In the summer colors become lighter with the light yellows and greens prevalent. Wings become pale gray and the bodes yellow or pale buff or olive.
In the autumn, mayflies return to the dark colors.
Mayflies have a incomplete life cycle: egg, nymph and adult.

Mayfly Stages

Mayflies have an incomplete life cycle: egg, nymph and adult:

Nymph - The immature stage of the mayfly that has hatched from the egg.  The nymph goes through several moltings as it grows in size.

Dun - the sexually immature stage of the adult mayfly that emerges from the nymphal shuck prior to a further molt to the sexually mature spinner.  Also know as the subimago.Hatch Video

Spinner - The sexually mature stage of the adult mayfly.  Also known as the imago.

Spent Spinner - The stage of the mature mayfly after it has deposited its eggs.

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Mayfly Groups

Mayflies are sometimes divided into four groups based on the behavior of the nymphs.

Group 1Group II


Group I mayfly nymphs have a front section � from beginning of head to rear edge of wing pad � that is as large or larger than the rear section � from end of wing pad to end of abdomen. Group I


Crawler � The width of the head includes eyes is similar or equal to the width of the abdomen, excluding the gills.

Clinger � The width of the head including eyes is always wider than the width of the abdomen, excluding gills.


Group II mayflies nymphs have a front section, from the beginning of the head to the rear edge of the wing pad, that is smaller than the rear section, from the end of the wing pad to the end of the abdomen.

Group II Swimmer

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