Mayfly · Aquatic insect
Sulphur
Ephemerella invaria
Size
7–10mm
Hook size
#16–14
Hatch window
Season May–JulyPeak time 18:00–dark
Water temperature
15° peak
11°21°
Hatches from 11°C, peaking at 15°C, tailing off by 21°C.How fish feed on it
By the time the spinners are down the fly has finished its job and is simply lying there, spent, wings flat in the film, going nowhere. Trout know the difference between something alive and something that's stopped trying, and they take spinners with a quiet, unbothered sip that's easy to miss if you're still watching for something splashier. Look for them on the glides and in the slack water, wherever the current gathers what's left.
Flies that imitate this
Sulphur Comparadun
Sulphur Sparkle Dun
Sulphur Spinner
Sulphur Emerger
Ecology
Where you'll find this
- North America — EastPresent
Present throughout
Identification
Ephemerella invaria , the sulphur dun , is a species of spiny crawler mayfly in the family Ephemerellidae. It is found in southeastern and northern Canada and the eastern United States.