PMD is a fisherman's acronym for Pale Morning Dun. In Montana they're usually ephemerella dorothea. Also often referred to as Sulfurs East of the Mississippi. The Females are lethargic, slightly larger and more olive. The males are more active, slightly smaller and far more yellow overall.
Female Pale Morning Dun

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Female-pmd
Female-pmd

Male-pmd-waving
Male-pmd-waving

PMD-nymph
PMD-nymph

Wing-goo
Wing-goo

Male-pmd
Male-pmd