Claws in front, tail fan behind, bottom underneath.
First checkAre there pincers much larger than the walking legs? Then it is a crayfish.
Nothing else in fresh water carries a pair of pincers that size. The claws settle the identification on their own; everything after that is about which crayfish and what condition it is in.
Two things about the animal matter more than its name. It lives on and in the bottom, and it walks forward slowly but escapes backwards in a hard flick of the tail fan. Those are two entirely different movements from the same animal.
The third is moult. A newly moulted crayfish is soft for two to four days and is the same animal, not a different one. Young crayfish moult six to fourteen times in a first year, so size within a season is not fixed.
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 Crayfish
Pincers or claws on the front legs+6
Fan-shaped tail; escapes by flicking rapidly backwards+5
Aquatic insect crawling on rock or debris+3
Two long antennae+3
Argues against it
A shell with no claws or pincers on it at all-6
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect-5
Moving as a school or tight bait cluster, not as a single insect-4
Body flattened side to side, often lying or swimming on its side-4
No hardened head capsule and no legs — soft and segmented throughout-4
Backs into wet sand rear end first-3
A pair of feathery antennae fanned out into the water-3
Back legs flattened into paddles-3
Body translucent — light passes through it, and the backbone or gut shows-3
Body flattened top to bottom — it lies flat with its back uppermost-3
A toothed blade projecting forward between the eyes-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.
Crayfish — Adultdrawn
Adult
Size in hand25–150 mm, excluding antennae and legs
What you see
One pair of pincers, far larger than the walking legs
Domed carapace with a triangular rostrum between the eyes
Segmented abdomen ending in a flat fan-like tail
Abdomen flattened top to bottom, not side to side
Where it turns up
On and in the bottom; under rocks and logs by day; burrowed in the substrate.
How it moves
Walks slowly forward; flicks rapidly backwards when threatened; active largely at night.
Cues this stage offers the comparison
Pincers or claws on the front legs
Fan-shaped tail; escapes by flicking rapidly backwards
Aquatic insect crawling on rock or debris
Two long antennae
Confused with
Telling it from what it isn't.
CrayfishvsScud / Amphipod
A body flattened side to side with no enlarged pincers is a scud. Crayfish is flattened top to bottom and has claws.
Where in the column it mattersNear the bottom. A bottom animal that is under a rock by day and walking on the bottom at night. Burrowing species spend most of their lives in the substrate itself.
Read from the record's own position notes: on and in the bottom; under rocks and logs by day; burrowed into the substrate; rarely far from the bottom.
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.
9 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 on basic counts — four pairs of walking legs plus chelipeds or five pairs with the first enlarged, and five or seven abdominal segments. Neither is offered as a field character.
Declared by the reviewerSize varies with moult stage; a single moult can add up to fifteen percent in length.
Declared by the reviewerNo source consulted states that crayfish enter the invertebrate drift, so this reference makes no such claim.
Declared by the reviewerSources disagree on basic counts: whether crayfish have four pairs of walking legs plus chelipeds or five pairs with the first enlarged, and whether the abdomen has five or seven segments. Neither count is offered as a field character.
Declared by the reviewerSize varies with moult stage. Young crayfish moult six to fourteen times in the first year and adults only one to three times, and a single moult can add up to fifteen percent in length.
Declared by the reviewerNo source consulted stated that crayfish enter the invertebrate drift, so this reference makes no claim that they do.
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 5 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. Walking forward on its legs, then the backward tail-flick retreat. Two locomotion modes, one of them this entry's cue.
Research institute · external video · title read back from the publisher 2026-09-09
Carry it on
Take the group to the next step.
These send the class of animal and the water this record is documented in. They do not send a sighting, because this page does not have one — you have not told it what you saw.
Which fish in this kind of water are documented eating this class of forage, and how they behave when they are.
What this forage class asks of the setup — the weight it wants, and where the chain gives first.
Keep the group on the day's record, so a later entry can be compared against what you were looking at.
Found an error?
This entry was written and drawn away from your water. If something here is wrong, say so — the report is assembled in your browser and sent only if you send it.