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 Terrestrials (ants, beetles, hoppers) 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
Terrestrials (ants, beetles, hoppers)
Fish-shaped forage silhouettedecisiveAt a glance
Yes
No
School or bait cluster, not a single insectdecisiveWatch it
Yes
No
Reported size
38–230 mm
2–76 mm
Water it is recorded in
river, stream, lake margin, lake open, reservoir, spring
river, stream, lake margin
How it moves
flashing school; coordinated turns
struggling or kicking on the surface; hopping on bank vegetation
Reference seasonality
Forage present: All year
Bank falls: Jun, Jul, Aug, Sep
The same for both: life stages.
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 Terrestrials (ants, beetles, hoppers)
A hopper is an insect. A school is not.
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.
Did it fall from the bank, or did it come up from the water? If you cannot tell, do not name it a terrestrial.
What it is
Terrestrial invertebrates are an important part of stream fish diets, especially in summer, and none of them lived in the water. Hoppers, ants and beetles arrive from the bank. The observation class is 'fallen terrestrial', not a hatch.
Stages
Fallen adult (2–76 mm: ants to about 25 mm, grasshoppers mostly 13–25 mm and up to 76 mm. No source here gives beetle sizes.)
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.
Typical windows
Bank falls (adult)
Patterns (correspondence)
Dave's Hopper · Fur Ant · Foam Beetle
Limits
Broad observation class only — not a species ID and not a hatch.