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 Caddisfly 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
Caddisfly
Terrestrials (ants, beetles, hoppers)
Fallen terrestrial (hopper, ant, beetle)decisiveAt a glance
No
Yes
Portable case or case-like structuredecisiveAt a glance
Yes
No
Hopper / grasshopper silhouettedecisiveAt a glance
Hardened head with softer worm-like abdomendecisiveClose look
Yes
No
Terminal prolegs or hooks at the reardecisiveClose look
Yes
No
How the wings restdecisiveAt a glance
Wings tent-like / inverted-V
Varies
Abdominal gills (plate or feather)decisiveClose look
Not diagnostic
No
Reported size
3–40 mm
2–76 mm
Life stages covered
larva, pupa, adult
adult
How it moves
crawling with case; swimming pupa
struggling or kicking on the surface; hopping on bank vegetation
Reference seasonality
Emergence: Sep, Oct, Nov
Bank falls: Jun, Jul, Aug, Sep
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
Trichoptera
Caddisfly
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.
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.
