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Blue-Winged Olive (Baetis spp.)
Mayfly, hatching March–May and September–November, active in water between 38 and 58°F, and imitated at #16–22. Recorded from the Wisconsin driftless and northern Wisconsin, where 1611 Wisconsin rivers on this site carry a page.
The broadest name in the box: a family of small olive-bodied mayflies with dusky blue-grey wings, Baetis and its relatives, running size 16 down to 22 with the smallest coming off in the coldest weather. Two broods a year account for the peak months of March, April and May and again September, October and November, and the working temperature band is 38 to 58 degrees — cold and cold-transitional water. The nymph is slim and fast-swimming, olive to brown, at home in almost any current, present year-round and the reason a small pheasant-tail is never wrong. Grey, drizzling days are the days; emergence is slow and film-bound, and a trailing-shuck emerger outfishes the dun most of the time. The dun itself rides a long way in cold water because it cannot get airborne quickly. The spinners are small and rusty and often fall in the morning, reversing the usual mayfly clock.
- #16–22Hook size
- 38–58°FWater, active
- Mar–May · Sep–NovPeak months
- 4Life stages fished
What it is
Mayfly · Baetis spp. · nymph → emerger → dun → spinner
The broadest name in the box: a family of small olive-bodied mayflies with dusky blue-grey wings, from Baetis and its relatives. Sizes run 16 down to 22 and the smallest come off in the coldest weather.
Two broods a year, spring and fall, and the worse the weather the better the hatch. Grey, drizzling, 45°F is the day.
When it hatches
Peak is March–May and September–November. 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 38°F to 58°F. On this map that is cold, cold-transitional water — the band crosses 1 of the three break 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 slim, fast-swimming nymph, olive to brown, at home in almost any current. It is present year-round and is the reason a small pheasant-tail is never wrong. |
| emerger | Cold, grey, drizzling days are BWO days, and the emergence is slow and film-bound. A trailing-shuck emerger outfishes the dun most of the time. |
| dun | Small olive body, upright grey wings, riding the surface a long way in cold water because it cannot get airborne quickly. |
| spinner | Small rusty spinners, often falling in the morning rather than the evening — one of the few mayflies that reverses the usual clock. |
Matching flies
8 patterns in this book imitate the 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.
- Higa's SOS nymph · #16–20 — Small, slim, and deadly in clear low water.
- Parachute Adams dry fly · #12–20 — Universal mayfly dun imitation. Every angler carries these.
- Perdigon nymph · #14–20 — Slim, epoxied, sinks like a stone. The euro-nymphing point fly.
- 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.
- Zebra Midge nymph · #18–24 — Two materials and a bead. The winter fly, and the fly for the last two feet of a tailout.
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.
- Basteen Creek northern Wisconsin
- Beaver Creek northern Wisconsin
- Blake Creek northern Wisconsin
- Bonita Creek northern Wisconsin
- Casco Creek northern Wisconsin
- Chickney Creek northern Wisconsin
- Cunningham Creek northern Wisconsin
- Devils River northern Wisconsin
- East Twin River northern Wisconsin
- Embarrass River northern Wisconsin
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.
- northern lower Michigan MI
- southern lower Michigan MI
- the Upper Peninsula MI
- the Wisconsin driftless WI
- northern Wisconsin WI
- the Virginia mountains VA
- the North Carolina mountains NC
- southeast Minnesota MN
Rivers in these regions with a page here
- Saint Croix River
- Adams Creek
- Alder Creek
- Alder Creek
- Allen Creek
- Allen Creek
- Allen Creek
- Allen Creek
- Allenton Creek
- Allequash Creek
- Alvin Creek
- Amo Creek
- Anderson Creek
- Annis Creek
- Apple Branch
- Apple Creek
- Apple River
- Arkansaw Creek
- Armstrong Creek
- Armstrong Creek
- Arnold Creek
- Ash Creek
- Auburn Lake Creek
- Augustine Creek
- and 1587 more
Related hatches
Same family, or overlapping this one's calendar on the same water.
- Hendrickson Ephemerella subvaria · Mayfly · April–May
- Blue Quill Paraleptophlebia adoptiva · Mayfly · April–May
- Mahogany Dun Paraleptophlebia spp. · Mayfly · September–October
- Light Cahill Maccaffertium ithaca · Mayfly · May–July
- Sulphur Ephemerella invaria · Mayfly · May–July