The comparison scores every group at once. This page is for the moment you already have a pair of names in mind — mayfly or stonefly, scud or sowbug, shad or alewife — and want the structures that keep them apart, in one look. Nothing here is a current hatch.
The differences, and nothing else
Best separating check: Fish-shaped forage silhouetteAt a glance It separates Baitfish / forage silhouette from Mayfly cleanly, and every pair of groups still in play differs on it and you can check it at a glance.
What to look at
Baitfish / forage silhouette
Mayfly
Fish-shaped forage silhouettedecisiveAt a glance
Yes
No
School or bait cluster, not a single insectdecisiveWatch it
Yes
No
Reported size
38–230 mm
2–40 mm
Water it is recorded in
river, stream, lake margin, lake open, reservoir, spring
Rows come from the reviewed diagnostic weights the comparison scores with. “Decisive” means one answer puts them at least four points apart — the carrier's own rule for a structure that separates a pair.
The two entries, side by side
Osteichthyes — not Insecta
Baitfish / forage silhouette
If it has fins and a school, stop calling it a bug.
First check
Count fins. If it schools, you are done naming insects.
What it is
This entry exists so a forage observation is not forced into an insect order. Minnows, shiners, fry and shad are not a hatch.
Stages
Forage fish (juvenile or adult) (About 38–230 mm across common baitfish species, fathead minnow to golden shiner)
Water
river, stream, lake-margin, spring
Separates from Mayfly
Any true insect tails rule out forage.
Typical windows
Forage present (adult)
Patterns (correspondence)
Clouser Minnow · Deceiver
Limits
Silhouette class only. Many genera exist; do not name a minnow from this card.
Count the tails, then look for gills along the sides of the abdomen. Three tails plus side gills is about as close to a clean mayfly call as field observation gets.
What it is
Mayflies are the only insects that grow a full set of working wings and then moult again. The winged insect that leaves the water is not the finished animal — it is a dun, a subimago, cloudy-winged and dull-bodied. Within hours to a couple of days it sheds one more time into a spinner: clear-winged, smooth and shiny, built only to mate and die. Two winged forms of the same animal, hours apart, sitting on the same water.
Stages
Nymph (2–32 mm) · Dun (subimago) (Under 4 to 40 mm body; most families 4–20 mm) · Spinner (imago) (Under 4 to 40 mm body; most families 4–20 mm)
Water
river, stream, lake-margin
Separates from Baitfish / forage silhouette
This entry does not name Baitfish / forage silhouette as a look-alike. That is a gap in the prose, not proof they cannot be confused.
