A grub with nothing to walk on and a head it keeps to itself.
First checkLook for legs. None at all, on a plump segmented grub, means a fly larva. Then look at the blunt back end for a disc ringed with lobes.
A cranefly larva is a plump, blunt, segmented grub, tan to grey to greenish, with a dark line of gut showing through the skin. It has no legs — and that is not a small observation, because one state assessment guide puts the whole order behind it: flies are the only aquatic insect whose larvae lack fully developed legs. If you can see three pairs of jointed legs, you are not holding one of these.
The rear end is where the identification actually lives. The abdomen finishes in a disc ringed by fleshy lobes or tentacle-like projections, and there are fleshy welts on the underside of some segments — swellings, not hooked prolegs. Compare a midge larva: hard visible head sticking out in front, thin worm-like body, two pairs of prolegs tipped with hooks, and sometimes bright red. Head and tail separate them. Size does not, and neither does habitat.
This entry ends with a gap rather than a flourish, and it is a real one. No source consulted describes how a cranefly larva moves, places it in the drift, or states that fish eat it. The picture of one tumbling helplessly down a riffle is supported by nothing reviewed here. That is an uncomfortable thing for a forage guide to admit about an animal half the fly bins in the country imitate — which is exactly why it is admitted rather than smoothed over.
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 Cranefly larvae
Head withdrawn into the front of the body, hard to see+8
Fleshy lobes or a disc at the blunt rear end+7
No long tail filaments visible+3
Aquatic insect crawling on rock or debris+1
Argues against it
Hardened head with softer worm-like abdomen-5
Terminal prolegs or hooks at the rear-5
Three tail filaments clearly visible-5
Extendable grasping mouthparts (labium / mask) on an aquatic nymph-5
Three leaf-like caudal lamellae at the tail (damselfly nymph) rather than round filaments-5
Hard wing covers (elytra) meeting in a straight line down the back-5
Wings held upright (sailboat posture)-5
Wings held tent-like or inverted-V over body-5
Wings held flat and parallel along the body-5
Winged insect at or near the surface-5
Fallen terrestrial insect (hopper, ant, beetle, etc.) — not an aquatic emergence-5
Hopper / grasshopper silhouette — hind legs long, body blocky, wings folded along back-5
Pinched waist (ant / flying ant) with elbowed antennae-5
One pair of long, flattened, oar-like hind legs used to row-5
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect-5
Two tail filaments clearly visible-4
Portable case or case-like structure present-4
Plate-like or feather-like abdominal gills visible-4
Gills at the thorax or leg bases-4
Air bubble or silvery film carried under water (diving beetle / water beetle)-4
Swims on its back, belly upwards-4
Mouthparts form a pointed beak rather than chewing jaws-4
Two long antennae-4
Moving as a school or tight bait cluster, not as a single insect-4
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
No hardened head capsule and no legs — soft and segmented throughout-2
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.
Cranefly larvae — Larvadrawn
Larva
Size in hand5–50 mm across the consulted sources, which disagree substantially
What you see
No legs at all
The rear end finishing in a disc ringed by fleshy lobes or tentacle-like projections
Fleshy welts on the underside of some abdominal segments — swellings, not hooked prolegs
A rounded head capsule present but usually withdrawn into the body and hard to see
Very small hairs along either side, and a translucent skin with the gut line visible inside
Where it turns up
On and in the substrate where decaying vegetation and leaf debris collect, in habitats from lakes and wetlands to fast water. A substantial share of the family is not aquatic at all.
How it moves
Classified as a crawler and burrower. That is the only movement statement any consulted source makes, and this entry does not add to it.
Cues this stage offers the comparison
Head withdrawn into the front of the body, hard to see
Fleshy lobes or a disc at the blunt rear end
No long tail filaments visible
Confused with
Telling it from what it isn't.
Cranefly larvaevsMidge (non-biting)
A hard dark head clearly out in front, a thin worm-like body and two pairs of hook-tipped prolegs is a midge. Bright red points that way too. Size and habitat separate nothing here.
No head, thorax or abdomen distinction at all, with bristle bundles along the whole body, is an aquatic worm. A cranefly larva has a head capsule, even a withdrawn one, and a distinct lobed tail disc.
These groups name Cranefly larvae in their own separators. If you arrived holding one of them and were not sure, this is the sentence that pointed you over.
Black fly larvasaid
Both are legless grubs. A cranefly larva is plump and even, with a rear disc ringed by fleshy lobes, and is not anchored in current.
Where in the column it mattersIn the substrate. In the bottom. Nothing consulted places a cranefly larva in the drift, so this reference does not put it there either — which is a different answer from the one most fly boxes imply.
Read from the record's own position notes: on and in the substrate, where decaying vegetation and leaf debris collect.
What eats it
Which fish the dossiers actually name.
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.
Nothing in the pattern layer is mapped to this group, so no presentation family follows from it here.
Not known
What this entry cannot tell you.
12 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 reviewerSources disagree about the head: one field guide says the larvae possess a definite head, an assessment guide says it is often reduced, barely visible and retracts so far that seeing it usually means cutting the thorax open. This entry follows the second.
Declared by the reviewerSize brackets conflict substantially, three of them from a single agency's own publications.
Declared by the reviewerNo consulted source describes how they move, places them in the drift, or states that fish eat them.
Declared by the reviewerThe name “leatherjacket” appears in no consulted source.
Declared by the reviewerSources disagree about the head. One state field guide says the larvae possess a definite head; a state assessment guide says the head capsule is often reduced, barely visible, and retracts so far that seeing it usually means cutting the thorax open. This record follows the second, and says so.
Declared by the reviewerSize brackets conflict substantially — 10 to 17 mm, 13 to 25 mm, 29 to 50 mm, and under 5 to over 50 mm, three of those from one agency's own publications.
Declared by the reviewerNo source consulted describes how cranefly larvae move, places them in the drift, or states that fish eat them. The angling picture of a cranefly larva tumbling helplessly down a riffle is supported by nothing consulted here. That is a real gap in a forage guide and is left visible rather than filled.
Declared by the reviewerNo source consulted describes gills, or names the tail structure a spiracular disc.
Sources disagreeHead visibility is a straight contradiction between two agencies, and it is the single character a beginner would reach for first.
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.
SeasonalityNo reference window is published for this group, so this entry says nothing about when it is available. That is an absence in the calendar layer, not a claim that the animal has no season.
PatternsNo fly pattern in the pattern layer is mapped to this group. Whether anything imitates it is not answered here.
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 7 published pages.
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.
Leaf Pack Network. The peristaltic, headless-looking crawl and the fleshy rear lobes flexing — why 'leatherjacket' describes a way of moving.
Research institute · external video · title read back from the publisher 2026-09-09
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