“Brush-legged Mayflies”
Family Overview
Isonychiidae
Brush-legged Mayflies
Isonychia is the only genus in the family Isonychiidae. There are about 15 known North American species. They have a widespread distribution east of the Rocky Mountains, and tend to be found swimming in fast-flowing water. They have a fusiform, minnow-like body shape, making them strong swimmers and clingers. Long setae (hair) on the inner margins of the femora and tibia of forelegs are used for filter feeding, a trait almost unique to this group of mayflies (also occurring in the rare family Oligoneuriidae). They are important in the trout and fly fishing community as "Slate Drakes" due to their frequent but periodic hatches (emergence of subimagos or "duns") and return to the water surface as spent adults (imagoes or "spinners") in June–October.
Characteristics
POLLUTION TOLERANCE
Mid-Atlantic: 2
Upper Midwest: 2
Midwest: 1.9
Southeast: 3.8
0 = least tolerant, 10 = most tolerant
FEEDING HABITS
Collector / Filterer
Engulfer / Predator
Engulfer / Predator
MOVEMENT
Clinger
Swimmer
Swimmer
Diagnostic Characters
Media
Isonychiidae
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