First checkIs there a sucker at both ends? That is a leech and nothing else.
One character does the whole job: a sucker at each end of the body. Everything a leech might be confused with fails that test.
The two confusions worth naming are the flatworm and the aquatic worm, and they fail in opposite directions. A flatworm has no segments and no suckers. An aquatic worm has segments and bristles but no suckers. A leech has segments and suckers and no bristles at all.
Note what does not help: both leeches and flatworms are flattened. Flattening on its own separates nothing.
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 Leech
A sucker at each end of the body+6
No hardened head capsule and no legs — soft and segmented throughout+4
Argues against it
Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect-5
Bundles of fine bristles along the segments-5
A row of leg-like flaps down both sides of the body-5
Moving as a school or tight bait cluster, not as a single insect-4
Head everts a proboscis carrying dark jaws-3
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.
Leech — Adultdrawn
Adult
Size in hand5–500 mm — it stretches, so treat any measurement as approximate
What you see
A sucker at each end of the body
Segmented, with each segment further wrinkled into annuli
No bristles anywhere
Flattened in cross section, not round like an earthworm
Where it turns up
On vegetation, under stones, in bottom muck; warm calm shallow water with thick weed.
How it moves
Graceful undulating swimming, or looping along like an inchworm using both suckers. Usually avoids light.
Cues this stage offers the comparison
A sucker at each end of the body
No hardened head capsule and no legs — soft and segmented throughout
Confused with
Telling it from what it isn't.
LeechvsAquatic worms
Bristle bundles along the segments and no suckers is an aquatic worm. Suckers and no bristles is a leech. The pair is reciprocal and reliable.
Where in the column it mattersNear the bottom. Mostly on vegetation, under stones or in bottom muck, but a leech will also travel along the underside of the surface film, so it is one of the few soft-bodied animals you may meet at the very top.
Read from the record's own position notes: on vegetation, under stones and logs, or in bottom muck; warm calm shallow water, especially where weed is thick; travels along the underside of the surface film.
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.
7 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 reviewerNo source consulted states whether leeches are nocturnal or day-active beyond the observation that they usually avoid light, and none addressed seasonal activity.
Declared by the reviewerNo source consulted reports leeches in the invertebrate drift.
Declared by the reviewerThe size range is wide because leeches stretch and contract dramatically.
Declared by the reviewerThe size range is very wide because leeches stretch; treat any observed length as approximate.
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 3 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.
Stroud Water Research Center. The swimming undulation and the inchworm crawl that alternately anchors each end — which is what makes 'a sucker at each end' visible.
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.