In hand the nymph reads as robust and flattened, with two tail filaments and two long antennae — a symmetry front and back that mayflies do not have. Gills, when you can see them, are thread-like or tufted and sit at the thorax and leg bases rather than ranking down the sides of the abdomen.MAINE-DEP-STONEFLY, MDC-STONEFLIES, MDC-MAYFLIESDispute
The adult holds its wings flat and parallel along the body, folded down over the back rather than tented or upright. Big western species crawl out onto rock and bank to emerge rather than emerging in the film, which is why you find shucks on dry stone.NCSU-ENT425-PLECOPTERA, MTFG-GIANT-SALMONFLY, MDC-STONEFLIESDispute
The tell
What settles it, and what settles against it.
Read off this record's own diagnostic weights, heaviest first. A structure near the top of the left column does most of the work on its own; one near the bottom only leans.
Argues for Stonefly
Wings held flat and parallel along the body+5
Gills at the thorax or leg bases+4
Two long antennae+4
Two tail filaments clearly visible+3
Aquatic insect crawling on rock or debris+3
Winged insect at or near the surface+1
Argues against it
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect-5
Fallen terrestrial insect (hopper, ant, beetle, etc.) — not an aquatic emergence-4
Moving as a school or tight bait cluster, not as a single insect-4
Portable case or case-like structure present-4
One pair of long, flattened, oar-like hind legs used to row-4
Swims on its back, belly upwards-4
Mouthparts form a pointed beak rather than chewing jaws-4
Fleshy lobes or a disc at the blunt rear end-4
Head withdrawn into the front of the body, hard to see-4
A single tail filament pointing straight back, and no paired hooks-4
Hopper / grasshopper silhouette — hind legs long, body blocky, wings folded along back-3
Pinched waist (ant / flying ant) with elbowed antennae-3
Hard wing covers (elytra) meeting in a straight line down the back-3
Extendable grasping mouthparts (labium / mask) on an aquatic nymph-3
No long tail filaments visible-3
No hardened head capsule and no legs — soft and segmented throughout-3
Swollen rear end gripping a rock in current, body standing up and waving downstream-3
Air bubble or silvery film carried under water (diving beetle / water beetle)-2
Three leaf-like caudal lamellae at the tail (damselfly nymph) rather than round filaments-2
Three tail filaments clearly visible-2
Hardened head with softer worm-like abdomen-2
Plate-like or feather-like abdominal gills visible-2
Wings held upright (sailboat posture)-2
Wings held tent-like or inverted-V over body-2
Terminal prolegs or hooks at the rear-1
A structure at −4 or below is treated as a hard exclusion by the comparison tool rather than as a penalty: if you saw it, this group is ruled out and no amount of matching elsewhere brings it back. Run a comparison →
Gill position is the honest separator. Stonefly gills tuft at the thorax and leg bases; mayfly gills are plate-like along the sides of the abdomen. Two tails alone proves nothing.
Caddis larvae carry a case or a hard head with terminal hooks and have no long tails or antennae. Caddis adults tent their wings; stonefly adults lie them flat.
Where in the column it mattersIn the substrate. Nymphs crawl rather than swim, and most crawl to the edge to emerge rather than rising through the column.
Read from the record's own position notes: subsurface under stones or debris; crawling on rock edges; adult near aquatic habitat.
Reference windows
When this group is typically available.
Typical published ranges only. Elevation, latitude, tailwater release and a given year's weather move all of these, often by weeks. This is never a statement about today.
4 reference windows
Nymphs presentnymph
JFMAMJJASOND
Most stoneflies spend one to two years as nymphs, and the giant salmonfly three to four, so large nymphs are in the water in every month.
No reviewed dossier names this group. That is an absence in the dossier layer rather than a finding about the animal — four dossiers exist and only one of them names any forage group at all.
The pattern layer ties this group in Nymph, Dry. That is a correspondence between an imitation and an animal, worked out when the patterns were written. Whether a fish is on it today is a question this page cannot reach.
Rubber-Legs Stonefly Nymph
Nymph
Hook4–12
A large stonefly nymph crawling among cobble.
Dead-drifted deep and slow. Weight matters more than profile because the natural does not swim.
Twenty-Incher
Nymph
Hook8–14
A medium stonefly nymph, with enough scruff to double as a large mayfly nymph.
Dead-drifted as an anchor fly. Deliberately broad in what it suggests.
Stimulator
Dry
Hook6–14
An adult stonefly on the surface with wings held flat along the body.
Dead-drifted or skittered against the bank where adults fall in.
Little Black Stonefly
Dry
Hook14–18
One of the small dark winter stoneflies.
Dead-drifted tight to the bank on cold bright days.
8 of them. The limits are part of what was reviewed rather than a disclaimer bolted on afterwards. An entry that hid them would be claiming more than it checked.
Written by the reviewer
Declared by the reviewerHabitat and emergence timing vary considerably by species.Dispute
Declared by the reviewerThis guide cannot establish a current observation, site-specific water status, or fishing success.Dispute
Declared by the reviewerTwo tails alone do not separate every stonefly from every mayfly.Dispute
Declared by the reviewerHabitat and emergence timing vary by species.Dispute
Declared by the reviewerThis record cannot establish a current observation, site-specific water status, or fishing success.Dispute
Sources disagree[object Object]
Sources disagree[object Object]
Read off the record
Nobody typed these. They are fields that are empty, said out loud rather than left for you to notice from a section that simply is not there.
What eats itNo reviewed species dossier names this group. Some dossiers describe forage in class terms — small forage, insects, bait — and those are shown below, but a class description is not a reviewed link to this group and none is claimed.
Sources
Everything above rests on 11 published pages.
These are every page behind this entry. Where a reviewer traced a line above to the pages that carry it, that line names them itself, with where the evidence comes from when it is narrower than the whole entry. A line with no names beside it rests on this list as a whole: nobody has yet checked which page carried it, and naming one would be a mapping nobody made.
A plate shows shape. It cannot show a gill beating, a mask firing, or an animal reversing into sand — so where motion is the field mark, the entry points at motion. These are demonstrations, selected by hand and by publisher. Nothing here is a source: it changes no score, no window and no reviewed claim.
Leaf Pack Network. A nymph doing push-ups to drive water over its thoracic gills. Gill position separates this group from a mayfly; the push-up is how you notice it.
Research institute · external video · title read back from the publisher 2026-09-09
Bug of the Week. Nymph and winged adult in the same field, in the season most anglers assume nothing is out.
Science media · external video · title read back from the publisher 2026-09-09
Carry it on
Take the group to the next step.
These send the class of animal and the water this record is documented in. They do not send a sighting, because this page does not have one — you have not told it what you saw.
Which fish in this kind of water are documented eating this class of forage, and how they behave when they are.
What this forage class asks of the setup — the weight it wants, and where the chain gives first.
Keep the group on the day's record, so a later entry can be compared against what you were looking at.
Found an error?
This entry was written and drawn away from your water. If something here is wrong, say so — the report is assembled in your browser and sent only if you send it.
