Not every caddis builds a house, and the ones that don't are the ones you miss.
First checkIgnore the case. Look for a hard dark head against a soft pale abdomen, and hooks at the back end.
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.
So the reliable caddis larva signal is not the case. It is the body plan: a hardened, darker head and forward thorax against a soft, pale, often worm-like abdomen, three pairs of legs clustered up near the head, and a pair of hooked prolegs at the tail end that grip rock, net, or case.
The winged adult is a different silhouette entirely — hairy wings folded tent-like or in an inverted V over the body, no long tails, and a moth-like flutter rather than a mayfly's upright drift.
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 Caddisfly
Portable case or case-like structure present+5
Hardened head with softer worm-like abdomen+4
Terminal prolegs or hooks at the rear+4
Wings held tent-like or inverted-V over body+4
No long tail filaments visible+1
Winged insect at or near the surface+1
Aquatic insect crawling on rock or debris+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
No hardened head capsule and no legs — soft and segmented throughout-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Head withdrawn into the front of the body, hard to see-4
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
Three tail filaments clearly visible-3
Wings held upright (sailboat posture)-3
Wings held flat and parallel along the body-3
A single tail filament pointing straight back, and no paired hooks-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
Plate-like or feather-like abdominal gills visible-2
Gills at the thorax or leg bases-2
Two long antennae-2
Two tail filaments clearly visible-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 →
Life stages
What it looks like, stage by stage.
Caddisfly — Larvaplate
Larva
Size in hand3–40 mm (most 5–25 mm)
What you see
Hardened, darker head and forward thorax against a soft pale abdomen
Three pairs of legs bunched near the head, none further back
Terminal prolegs with hooks at the rear
Sometimes — not always — a portable case of sand, leaf, or twig
Where it turns up
Subsurface on and under rock, in leaf packs, or inside a fixed retreat with a spun net beside it in flowing water.
How it moves
Case-bearers drag the case along, head and legs protruding. Free-living forms crawl quickly and curl when handled.
Cues this stage offers the comparison
Portable case or case-like structure present
Hardened head with softer worm-like abdomen
Terminal prolegs or hooks at the rear
Aquatic insect crawling on rock or debris
Caddisfly — Pupaplate
Pupa
Size in hand4–30 mm
What you see
Wings and legs visible but folded against the body, not yet functional
Often a gas bubble sheen trapped under the pupal skin
Long trailing legs held back along the body while rising
No case — the pupa has cut free of it
Where it turns up
Rising through the water column toward the surface, or already in the film working to break through.
How it moves
Actively swims upward, often in an urgent, darting rise rather than a passive drift.
Cues this stage offers the comparison
No long tail filaments visible
Hardened head with softer worm-like abdomen
Caddisfly — Adultplate
Adult
Size in hand4–25 mm
What you see
Hairy wings held tent-like or in an inverted V over the body at rest
No long tail filaments at all
Long antennae swept forward, often as long as the body or longer
Moth-like appearance, but held tight rather than flat
Where it turns up
On streamside vegetation, on the water during egg-laying, and in the air over riffles at dusk.
How it moves
Erratic fluttering flight. Egg-laying females may dive or swim down, which is why a sunk adult is not a contradiction.
Cues this stage offers the comparison
Wings held tent-like or inverted-V over body
Winged insect at or near the surface
No long tail filaments visible
Confused with
Telling it from what it isn't.
CaddisflyvsMayfly
Wing posture at rest settles it: caddis tents its wings over the body, mayfly holds them upright like a sail. And caddis adults have no long tails.
Stonefly adults hold their wings flat and parallel along the body, not tented. Stonefly nymphs have two long tails and two long antennae; caddis larvae have neither.
At arm's length on a stone, a grit-built caddis case and a snail shell look the same. Pick it up: a caddis case has a jointed head and legs coming out of the front, a snail has a soft foot that grips your finger.
A caddis case is built of glued grit and has a jointed head and legs coming out of it. A clam is a shell the animal grew, with nothing coming out but a foot.
Where in the column it mattersNear the bottom. Larvae are on or in the bottom; the pupa crosses the whole column to emerge, which is why the ascent matters more than the resting place.
Read from the record's own position notes: subsurface (larva/pupa); surface or near-surface (emergence); resting with tent wings.
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.
3 reference windows
Available year-roundlarva
JFMAMJJASOND
Cased and free-living larvae are present continuously; free-living forms are more available in the drift.
All day
Emergencepupa
JFMAMJJASOND
Pupae rise fast and actively rather than drifting up. That is the mechanism people reach for when a dead-drifted fly gets refused and a rising one does not — a reasonable read of how the insect moves, and not something this reference has watched happen.
50–62 °F · Afternoon into dusk
Egg-layingadult
JFMAMJJASOND
Females may dive or crawl underwater to lay. A sunk adult is normal behaviour, not an anomaly.
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, Emerger, Pupa. 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.
Elk Hair Caddis
Dry
Hook12–20
An adult caddis at rest with its wing tented over the body.
Dead-drifted, or twitched and skated to suggest egg-laying movement.
X-Caddis
Emerger
Hook14–20
An emerging caddis still hung in its trailing shuck.
Fished in the film. The trailing shuck is the whole point of the pattern.
Sparkle Pupa
Pupa
Hook12–18
A rising caddis pupa carrying a gas bubble under its pupal skin.
Swung or lifted through the last of the water column rather than dead-drifted.
Green Rock Worm
Nymph
Hook12–18
A free-living caddis larva tumbling loose in the drift.
Dead-drifted on the bottom. Tied curved to suggest the larva's natural hook shape.
6 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 reviewerCase-building behavior varies and absence of a visible case does not rule out caddis.
Declared by the reviewerThis guide does not claim a current emergence or recommend a specific pattern as correct.
Declared by the reviewerBroad group only; many families exist and differ substantially.
Declared by the reviewerThis preview does not claim a current emergence or recommend a specific pattern.
Declared by the reviewerBroad group only; many families exist.
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 1 published page.
Attribution here is to the whole record, not to individual sentences — the carrier attaches a source set to a record and does not say which page carried which line. Naming one per claim would mean inventing a mapping nobody reviewed.
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.
Deep Look. The larva spinning silk and building its case underwater, which is what makes the portable case a behaviour rather than an ornament.
Science media · external video · title read back from the publisher 2026-09-09
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