First checkPut it flat on a wet palm. If it lies there back-up, it is a sowbug. If it rolls onto its side, it is a scud.
Sowbugs and scuds are the same size, live in the same water, and both have seven pairs of walking legs. Almost everything written about telling them apart is a list of characters you would need a lens for.
One character does not need a lens: which way the animal is squashed. A sowbug is flattened top to bottom, so it sits flat in a wet palm with its back uppermost and stays there. A scud is flattened side to side, so it falls onto its flank.
The behaviour agrees with the shape. A sowbug crawls, slowly and deliberately, over rock and wood. It does not swim in open water, and it does not flick.
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 Aquatic sowbug
Body flattened top to bottom — it lies flat with its back uppermost+6
Aquatic insect crawling on rock or debris+3
Two long antennae+3
Argues against it
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
Pincers or claws on the front legs-4
Fan-shaped tail; escapes by flicking rapidly backwards-4
A shell with no claws or pincers on it at all-3
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
A toothed blade projecting forward between the eyes-3
Body translucent — light passes through it, and the backbone or gut shows-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.
Aquatic sowbug — Every stage — they all look the samedrawn
Every stage — they all look the same
Size in hand5–20 mm
What you see
Flattened top to bottom; broad and plate-like from above
Seven pairs of walking legs, all much the same
Two pairs of antennae, one pair conspicuously long
No tails, no wing pads, no gills along the sides
Where it turns up
Springs and spring branches, small streams, shallow pond and lake margins — under rocks, wood and debris on the bottom.
How it moves
A slow crawl over hard surfaces. Never a swimmer, never a flicker.
Cues this stage offers the comparison
Body flattened top to bottom — it lies flat with its back uppermost
Aquatic insect crawling on rock or debris
Two long antennae
Confused with
Telling it from what it isn't.
Aquatic sowbugvsScud / Amphipod
The flattening axis, and it is the whole tell: a sowbug is squashed top to bottom and lies flat, a scud is squashed side to side and lies on its flank. If the animal is also C-curved and darting, it is a scud.
Where in the column it mattersNear the bottom. On the bottom and under it. A sowbug crawls; nothing consulted describes it swimming, so this reference does not put it in the column.
Read from the record's own position notes: under rocks, wood and debris on the bottom; among sediment and vegetation in seeps and spring branches.
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 reviewerFamily level only. This does not separate Caecidotea from Asellus, and it does not tell a surface animal from a groundwater one.
Declared by the reviewerSize says nothing about age here — every stage is the same shape, so a 6 mm and a 19 mm sowbug are the same animal at different times.
Declared by the reviewerSowbugs are crawlers rather than behavioural drifters, so this entry makes no claim about when one would be in the drift.
Declared by the reviewerA sowbug result is the family level. It does not separate Caecidotea from Asellus, and it does not distinguish a surface-water animal from a groundwater one.
Declared by the reviewerSize is not a stage cue here: every stage looks the same, so a 6 mm animal and a 19 mm animal are the same shape and tell you nothing about age.
Declared by the reviewerSowbugs are crawlers rather than behavioural drifters. This record says nothing about when one would be available in the drift.
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 4 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.
Let's Scope it out!. The life stages, including the brood pouch and juveniles — a size range that explains a lot of misidentified small specimens.
Science media · 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.