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Large Blue-Winged Olive (Drunella cornuta)
Mayfly, hatching May–June, active in water between 50 and 64°F, and imitated at #14–16. Recorded from the North Carolina mountains, where 1575 North Carolina rivers on this site carry a page.
- #14–16Hook size
- 50–64°FWater, active
- May–JunPeak months
- 4Life stages fished
What it is
Mayfly · Drunella cornuta · nymph → emerger → dun → spinner
A stout olive mayfly with dark grey wings and three tails, at a #14 or #16 — three or four sizes larger than the autumn Baetis that share the name. The nymph is a heavily built crawler with spined, mossy-looking legs.
Not the little autumn Baetis everyone means by 'BWO' — a #14 olive dun off on cold mornings in the southern Appalachian spring. Anglers fishing a #20 through it are the standard reason the hatch gets called unproductive.
When it hatches
Peak is May–June. The pale months either side are the shoulder — the app widens a peak by one month in each direction and recommends the bug there, and no further: that widening is bounded so that a bug peaking in May is never offered in August.
peak shoulder not recommended
Water conditions
The band is a water temperature, not an air temperature, and it is the range in which this insect is worth fishing — for a mayfly that is the emergence window; for a scud or a midge it is simply the range trout will still eat one in.
Active from 50°F to 64°F. On this map that is cold, cold-transitional, cool water — the band crosses 2 of the three breaks the river colours use. Breaks at 58, 64 and 70°F.
Stages
What the insect is doing, and what that means for what you tie on.
| Stage | What it is |
|---|---|
| nymph | A robust crawler in cobble, dark olive-brown and often camouflaged with debris. Available for months before the hatch. |
| emerger | In the film on cool mornings. Slow emergence in cold water is the point of the hatch, and a stuck-shuck pattern is often the fly. |
| dun | Olive-bodied, dark-winged and large. The single most common mistake on this hatch is fishing it at #20 because the name says blue-winged olive. |
| spinner | Falls in the evening, considerably less fished than the morning dun. |
Matching flies
5 patterns in this book imitate the Large Blue-Winged Olive, across its stages. Which one to tie on follows the stage the water temperature says it is in — the app makes that call on a live reading; this page lists the whole set.
- BWO Comparadun emerger · #18–22 — Flush-floating. Baetis emerge in the film and the fish know it.
- Parachute BWO dry fly · #16–22 — Olive body, grey post. The fly for a cold grey day in April or October.
- Hare's Ear Nymph nymph · #10–18 — Looks like everything and nothing. The other half of a two-nymph rig.
- Pheasant Tail Nymph nymph · #12–22 — The mayfly nymph. Beadhead or not, size 16, and half the trout in the world have eaten one.
- RS2 emerger · #16–24 — The emerger that saves a hatch you cannot otherwise crack. Fish it in the film.
Where to find it right now
The rivers with a page here that sit in this insect's regions, with a USGS gauge reporting water temperature. This list is re-ranked against the reading each gauge is sending now and today's date, so it is live — the fallback below it, if the readings do not arrive, is each river's measured July mean.
- Back Creek the North Carolina mountains · July mean 59.3°F
- Beaverdam Creek the North Carolina mountains · July mean 59.3°F
- Bill Davenport Branch the North Carolina mountains · July mean 59.3°F
- Bill White Creek the North Carolina mountains · July mean 59.3°F
- Black Fork the North Carolina mountains · July mean 59.3°F
- Bridge Branch the North Carolina mountains · July mean 59.3°F
- Brier Creek the North Carolina mountains · July mean 59.3°F
- Buckwheat Branch the North Carolina mountains · July mean 59.3°F
- Bull Branch the North Carolina mountains · July mean 59.3°F
- Cambric Branch the North Carolina mountains · July mean 59.3°F
Regional presence
Regions, not collection records. This insect is recorded from the coarse regions below; nobody has surveyed which named river it has been caught on, and this page will not pretend otherwise.
- the Virginia mountains VA
- the North Carolina mountains NC
Rivers in these regions with a page here
- Catawba River
- Aaron Creek
- Acorn Branch
- Adamcamp Branch
- Aiken Mill Creek
- Alarka Creek
- Alfred Creek
- Allison Creek
- Allmon Creek
- Ammons Branch
- Amos Creek
- Amos Creek
- Anderson Creek
- Anderson Creek
- Anderson Creek
- Anderson Creek
- Andrews Creek
- Anthony Bolick Branch
- Anthony Creek
- Appletree Branch
- Ararat River
- Armstrong Creek
- Arrowhead Branch
- Arrowwood Creek
- and 1551 more
Related hatches
Same family, or overlapping this one's calendar on the same water.
- Green Drake Ephemera guttulata · Mayfly · May–June
- Light Cahill Maccaffertium ithaca · Mayfly · May–July
- Little Sulphur Ephemerella dorothea · Mayfly · May–July
- March Brown Maccaffertium vicarium · Mayfly · May–June
- Sulphur Ephemerella invaria · Mayfly · May–July