Plural of greyfly; insects belonging to the mayfly family, typically with grey-colored wings.
Compound from 'grey' plus 'flies' (plural of fly). The term is used in fly fishing and entomology to refer to mayfly species with grey coloration.
Fly fishermen have incredibly detailed names for insect life stages and colorations because their livelihood depends on matching the exact flies fish are eating—'grey dun,' 'pale watery dun,' each referring to specific insect hatches.
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