“Brush-legged Mayflies”
Genus Overview
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 unique to this group of mayflies. They are important in the trout and fly fishing community due to their frequent but periodic hatches (emergence of subimagos) in June–October.
Characteristics
POLLUTION TOLERANCE
Southeast: 3.8
Upper Midwest: 2
Midwest: 1.9
Mid-Atlantic: 2
0 = least tolerant, 10 = most tolerant
FEEDING HABITS
Collector / Filterer
Engulfer / Predator
Engulfer / Predator
MOVEMENT
Clinger
Swimmer
Swimmer
DISTRIBUTION
Widespread (east of the Rocky Mtns.)
HABITAT
Lotic-erosional
Diagnostic Characters
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