Calendar of Insect Hatches

by Fly Fisherman

The transitions of these aquatic insects from nymphs or larvae to adults—or the coming up through the water of the nymphs and larvae to get ready for the adult stage—is called a hatch. This is the time when trout feed most heavily on aquatic insects and is the best time for fly fishing. Certainly it will pay any fly fisherman to study carefully the habits of the aquatic insects of trout streams.
The time when hatches of aquatic insects occur depends upon water temperature more than calendar date; and also varies greatly in different sections. In Eastern trout streams, the usual sequence of hatches of chief interest to anglers runs like this:

In April (1) Blue Quill;   (2) Quill Gordon and  (3) Dark Olive.

In May (1) Hare’s Ear; (2) March Brown; (3) Whirling Dun or Dark Cahill; and (4) Shad Fly.

In June (1) Flight’s Fancy; (2) Light Cahill; and (3) Pale Evening Dun.

It is interesting to note that 75 percent of the fish food that a trout stream holds is found in the riffles. Shallow, sun-flooded riffles hold more aquatic food than deep or shady ones.The life of adult aquatic insects is short. Some live but a few hours, other varieties several days. While in the air the adult aquatic insects join in the nuptial flight, mate in mid-air, and then return to the surface of the water to lay their eggs and die. Insects that have fulfilled their natural mission float downstream on the surface of the water. While alive they drift with wings erect and are supported on the surface by their legs and feet. As soon as they die, their wings flatten out side-wise and they float awash. In this stage they are called spent spinners. Spent-wing flies are imitations of this group.

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