Giant Black Stonefly (Salmonfly) (Pteronarcys dorsata)

Stonefly, hatching May, active in water between 50 and 62°F, and imitated at #4–6. Recorded from southeast Minnesota, where 99 Minnesota rivers on this site carry a page.

#4–6Hook size
50–62°FWater, active
MayPeak months
2Life stages fished

Subbasins with trout water where it is on record: 5 of Minnesota's 72.

See Minnesota's trout water on the live map → Every reach coloured by water temperature — the water these hatches come off.

What it is

Stonefly · Pteronarcys dorsata · nymph → adult

The largest insect in these rivers — a stonefly nymph two inches long, glossy black-brown, with two tails and two hooked claws on each leg. Multi-year life cycle, so the nymph is in the river every day of every year.

The eastern cousin of the western salmonfly. The emergence is at night and easy to miss; the nymph is a year-round meal.

When it hatches

These are Minnesota's own dates, not this site's shared calendar. They are the Giant Black Stonefly (Pterynarcys sp.) row of Hatch Chart for Southeast Minnesota Trout Streams, Minnesota Department of Natural Resources, Lanesboro Area Fisheries (Vaughn Snook, Assistant Fisheries Supervisor), as of 15 June 2016. The chart's calendar runs January to October and makes no claim about November or December. Its own footer says it is a general time frame, that some streams have only a few of these hatches, and that others may see hatches it does not list.

Peak is May. 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.

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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.

50°F 62°F

Active from 50°F to 62°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	Crawls among cobble and woody debris. Dislodged constantly, and a big black rubber-legged nymph is a searching fly on any river that holds them.
adult	Crawls to the bank to hatch rather than emerging in open water, which is why the nymph matters more than the dry. Adults return to lay eggs at dusk.

Matching flies

4 patterns in this book imitate the Giant Black Stonefly (Salmonfly), 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.

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.

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
the Upper Peninsula MI
northern Wisconsin WI
the Virginia mountains VA
southeast Minnesota MN

Rivers in these regions with a page here

Related hatches

Same family, or overlapping this one's calendar on the same water.

Open the trout map →Every trout stream near you, coloured by today's water temperature.