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Hellgrammite (Corydalus cornutus)
Other, in the drift all year, active in water between 55 and 78°F, and imitated at #2–8. Recorded from southern lower Michigan, where 155 Michigan rivers on this site carry a page.
- #2–8Hook size
- 55–78°FWater, active
- all yearAvailable
- 2Life stages fished
What it is
Other · Corydalus cornutus · larva → adult
The largest invertebrate in the river: up to three inches of dark, armoured, flattened larva with visible pincers, lateral filaments and a pair of hooked prolegs at the tail. The adult dobsonfly is enormous and unmistakable.
The dobsonfly larva: three inches of armoured, pincered nymph living under cobble in warm freestone rivers. It is the largest single invertebrate meal in southern Appalachian water and the reason a big black rubber-legged nymph works there all summer.
When it hatches
In the water twelve months a year, which is why the panel in the app ranks it below anything with a season.
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 55°F to 78°F. On this map that is cold, cold-transitional, cool, warm water — the band crosses 3 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 |
|---|---|
| larva | Lives several years under cobble in warm freestone rivers, hunting. Available every day, and worth fishing deliberately in the southern Appalachians where a single one is a substantial meal. |
| adult | The dobsonfly, huge and short-lived, on the water only by accident. It is the larva that trout and smallmouth are eating. |
Matching flies
4 patterns in this book imitate the Hellgrammite, 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.
- Girdle Bug nymph · #6–12 — Rubber legs on a chenille body. The cheap ancestor of Pat's Rubber Legs.
- Hellgrammite nymph · #2–8 — Big, black, rubber-legged and heavy. A southern Appalachian summer fly for trout and smallmouth in the same water.
- Pat's Rubber Legs nymph · #4–10 — Ugly, heavy, and the single best searching nymph in high or coloured water.
- Woolly Bugger (Black) streamer · #2–12 — If you could only own one fly. Leech, sculpin, big nymph, all of it.
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.
- Blue Lake Drain southern lower Michigan · July mean 66.0°F
- Fivemile Creek southern lower Michigan · July mean 66.0°F
- Flinton Creek southern lower Michigan · July mean 66.0°F
- James Creek southern lower Michigan · July mean 66.0°F
- Martin Creek southern lower Michigan · July mean 66.0°F
- Mena Creek southern lower Michigan · July mean 66.0°F
- Mullen Creek southern lower Michigan · July mean 66.0°F
- Rattlesnake Creek southern lower Michigan · July mean 66.0°F
- Rosy Run southern lower Michigan · July mean 66.0°F
- Second Cole Creek southern lower Michigan · July mean 66.0°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.
- southern lower Michigan MI
- the Wisconsin driftless WI
- the Virginia mountains VA
- the North Carolina mountains NC
Rivers in these regions with a page here
- Kalamazoo River
- Apel Drain
- Augusta Creek
- Bancroft Noles Drain
- Bassett Creek
- Bear Creek
- Bear Creek
- Belle River
- Bennett Creek
- Big Creek
- Big Dailey Bayou
- Big and Outlet Drain
- Bigelow Creek
- Black River
- Black River Canal
- Blue Lake Drain
- Brandy Creek
- Brayton Drain
- Brooks Creek
- Bunton Drain
- Butler Creek
- Camp Brook Drain
- Cave Creek
- Cedar Creek
- and 131 more
Related hatches
Same family, or overlapping this one's calendar on the same water.
- Cranefly Tipula spp. · Other · April–June and September–October
- Water Boatman Corixidae · Other · September–November
- Fish Eggs Other · Other · October–January and April
- Alderfly Sialis spp. · Other · May–June
- Aquatic Worm Oligochaeta · Other · all year