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: Hopper / grasshopper silhouetteAt a glance It separates Terrestrials (ants, beetles, hoppers) from Caddisfly cleanly, and every pair of groups still in play differs on it and you can check it at a glance.
What to look at
Terrestrials (ants, beetles, hoppers)
Caddisfly
Fallen terrestrial (hopper, ant, beetle)decisiveAt a glance
Yes
No
Portable case or case-like structuredecisiveAt a glance
No
Yes
Hopper / grasshopper silhouettedecisiveAt a glance
Hardened head with softer worm-like abdomendecisiveClose look
No
Yes
Terminal prolegs or hooks at the reardecisiveClose look
No
Yes
How the wings restdecisiveAt a glance
Varies
Wings tent-like / inverted-V
Abdominal gills (plate or feather)decisiveClose look
No
Not diagnostic
Reported size
2–76 mm
3–40 mm
Life stages covered
adult
larva, pupa, adult
How it moves
struggling or kicking on the surface; hopping on bank vegetation
crawling with case; swimming pupa
Reference seasonality
Bank falls: Jun, Jul, Aug, Sep
Emergence: Sep, Oct, Nov
The same for both: water.
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
Various — not an aquatic hatch order
Terrestrials (ants, beetles, hoppers)
It did not hatch here. It fell.
First check
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 Caddisfly
A portable case or tent wings at rest is caddis. A hopper hind-leg or ant waist on the film is a terrestrial.
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.
Not every caddis builds a house, and the ones that don't are the ones you miss.
First check
Ignore the case. Look for a hard dark head against a soft pale abdomen, and hooks at the back end.
What it is
Caddis is the group most often identified by a thing that is only sometimes there. The portable case — grains of sand, cut leaf, twig fragments, spun into a tube the larva carries — is the classic image, and when you find one the call is easy. But a large share of caddis larvae never build a portable case at all. Free-living forms hunt loose among the rocks; net-spinners build a fixed retreat with a catch-net beside it and leave the retreat behind when disturbed.
Stages
Larva (3–40 mm (often 13–25 mm with case)) · Pupa (No source consulted gives a pupal size) · Adult (4–38 mm)
Water
river, stream, lake-margin
Separates from Terrestrials (ants, beetles, hoppers)
A pinched waist or hopper hind legs on the film is a fallen land insect. Tent wings or a case is caddis.
Typical windows
Larvae present (larva) · Emergence (pupa)
Patterns (correspondence)
Elk Hair Caddis · X-Caddis · Sparkle Pupa · Green Rock Worm · Peeking Caddis
Limits
Case-building behavior varies and absence of a visible case does not rule out caddis.
