Light Cahill Mayfly vs Flat-headed Mayfly

Side-by-side species comparison

Attribute Light Cahill Mayfly Flat-headed Mayfly
Scientific Name Heptagenia solitaria Epeorus assimilis
Order Ephemeroptera Ephemeroptera
Family Heptageniidae Heptageniidae
Size 9-13 mm 10-14 mm
Habitat Rivers & Streams Rivers & Streams
Diet Omnivores Herbivores
Regions North America Europe
Conservation Least Concern Least Concern

Light Cahill Mayfly

A pale-colored mayfly highly prized by fly fishers for imitating hatches. Nymphs prefer moderate current over gravel substrates.

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Did You Know?

The Light Cahill dry fly pattern, designed to mimic this species, has been used since the 1880s.

Flat-headed Mayfly

A stream-dwelling mayfly nymph with a flattened body for clinging to rocks in rapids.

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Did You Know?

Its flattened nymph shape allows it to live in the boundary layer of fast currents.