Albert R. Mann Library
The dun stage of a Black Quill mayfly

The process in which the adult or sub-adult form of an aquatic insect emerges from its nymph or pupal form, and leaves the water. During emergence, the insect is particularly vulnerable to predation; mayfly nymphs, for example, must journey from the relative safety of the stream bed to the surface of the water, and then hang, helpless, as they struggle from their exoskeletons. In many species, local populations of a particular insect will all emerge simultaneously, and trout will feed voraciously, and exclusively, on them. In fly-fishing terminology, this is β€œthe hatch.”

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