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Hemiptera (Notonectidae)

Backswimmers

Upside down, keeled like a hull, and it does bite.

First checkWhich way up? Belly upwards, on a body keeled down the back, is a backswimmer. Then check the mouth is a beak, not jaws — that is what makes it a bug and not a beetle.

A backswimmer swims on its back. Two independent sources state it plainly — belly-up, ventral side facing upwards — which makes it the settled half of a pair that is otherwise easy to muddle. Its back, which is underneath while it swims, is keeled like the bottom of a boat, and carries a dark V-shaped mark rather than the ruled crosslines a water boatman has.

It is also the predator of the two. Grasping front and middle legs, piercing tube-like mouthparts, large dark red eyes, and an ambush habit — sitting part-way up a plant stem waiting. It preys on aquatic insects and on small fish and tadpoles, and one extension account adds fish eggs and fry to the list. It will deliver a bite if you handle it, which is another thing a water boatman will not do.

The thing to be careful of is the surface posture, because it is the character most people use and it does not work. A backswimmer rests tilted head-down with the tip of its abdomen through the film — and a predaceous diving beetle, per the same publisher, hangs head downward with the tip of its abdomen protruding from the water surface. Identical description, different order of insect. Use the mouth: beak or jaws.

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 Backswimmers

  • Swims on its back, belly upwards+8
  • One pair of long, flattened, oar-like hind legs used to row+6
  • Mouthparts form a pointed beak rather than chewing jaws+6
  • Air bubble or silvery film carried under water (diving beetle / water beetle)+3
  • No long tail filaments visible+2
  • Wings held flat and parallel along the body+1
  • Winged insect at or near the surface+1

Argues against it

  • Hard wing covers (elytra) meeting in a straight line down the back-5
  • Fish-shaped forage silhouette (minnow / shiner / fry) — not an insect-5
  • Fallen terrestrial insect (hopper, ant, beetle, etc.) — not an aquatic emergence-4
  • Hopper / grasshopper silhouette — hind legs long, body blocky, wings folded along back-4
  • Pinched waist (ant / flying ant) with elbowed antennae-4
  • Portable case or case-like structure present-4
  • Three tail filaments clearly visible-4
  • Plate-like or feather-like abdominal gills visible-4
  • Extendable grasping mouthparts (labium / mask) on an aquatic nymph-4
  • Three leaf-like caudal lamellae at the tail (damselfly nymph) rather than round filaments-4
  • Two long antennae-4
  • Fleshy lobes or a disc at the blunt rear end-4
  • Head withdrawn into the front of the body, hard to see-4
  • A single tail filament pointing straight back, and no paired hooks-4
  • Two tail filaments clearly visible-3
  • Gills at the thorax or leg bases-3
  • Hardened head with softer worm-like abdomen-3
  • Terminal prolegs or hooks at the rear-3
  • Wings held upright (sailboat posture)-3
  • Wings held tent-like or inverted-V over body-3
  • Moving as a school or tight bait cluster, not as a single insect-3
  • Swollen rear end gripping a rock in current, body standing up and waving downstream-3
  • Aquatic insect crawling on rock or debris-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.

AT THE SURFACE — SO IS A BEETLE
Backswimmers — Nymphdrawn

Nymph

Size in hand2–10 mm

What you see

  • A small wingless version of the adult, swimming the same way up
  • Wings arrive at the final moult and not before

Where it turns up

Ponds and quiet water, clinging to submerged vegetation.

How it moves

Rows belly-up, like the adult.

Cues this stage offers the comparison

  • Swims on its back, belly upwards
  • One pair of long, flattened, oar-like hind legs used to row
  • Mouthparts form a pointed beak rather than chewing jaws
AT THE SURFACE — SO IS A BEETLE
Backswimmers — Adultdrawn

Adult

Size in hand10–29 mm, and the sources bracket it three different ways

What you see

  • Swims on its back, belly upwards
  • Back keeled like a hull, with no crosslines across it
  • Piercing tube-like mouthparts — a beak, not chewing jaws
  • Large dark red eyes
  • Grasping front and middle legs; long oar-like hind legs
  • A thin silvery bubble of air trapped against the body

Where it turns up

Ponds and quiet areas of lakes and streams, usually part-way up a plant stem.

How it moves

Rows belly-up; rests tilted head-down at the surface with the abdomen tip through the film; ambushes rather than chases.

Cues this stage offers the comparison

  • Swims on its back, belly upwards
  • One pair of long, flattened, oar-like hind legs used to row
  • Mouthparts form a pointed beak rather than chewing jaws
  • Air bubble or silvery film carried under water (diving beetle / water beetle)

Confused with

Telling it from what it isn't.

BackswimmersWater boatmen

Right-way-up swimming, a flat back ruled by dark parallel crosslines, and scoop-shaped front feet is a boatman. It also does not bite, and this one does.

Open Water boatmen →

BackswimmersAquatic beetles

Head-down at the surface settles nothing — a diving beetle does exactly the same. Look at the mouth: a beak is a bug, chewing jaws are a beetle. Hard wing covers meeting in a straight seam are a beetle too.

Open Aquatic beetles →

Water and depth

Where the record puts it.

Water types documented

  • lake margin
  • reservoir
  • stream
  • river
  • spring

Where in the column it mattersSurface film. Hangs from the film upside down between hunts, which puts it in the one band an angler can actually see into.

Read from the record's own position notes: a backswimmer rests tilted head-down at the surface with the tip of its abdomen through the film.

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.

1 reference window
Overwinter in the wateradult

Overwinters as an adult in the water rather than leaving it. One published behavioural threshold, for a European species, has it spending most of its time submerged below about 59 °F air temperature — quoted here as an observation about one animal, not a rule for the family.

More active in the dark than in the light

See the full seasonality view →

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.

Forage described only in class terms

What that implies for presentation

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.

10 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 reviewerThe most detailed account consulted covers a Eurasian species; its air-film duration, temperature behaviour and one-brood-a-year seasonality are not offered here as North American facts.
  • Declared by the reviewerNothing consulted states that backswimmers are important forage for fish — the same source describes them eating fish eggs and fry, which is the food web running the other way.
  • Declared by the reviewerBite severity differs between two sources, though both agree it takes handling.
  • Declared by the reviewerSize is stated three incompatible ways — usually under half an inch, about 13 mm, and a bracket class of 15 to 29 mm. The band spans them.
  • Declared by the reviewerThe most detailed account consulted covers a Eurasian species. Its air-film duration, temperature behaviour and one-brood-a-year seasonality are not offered here as North American facts.
  • Declared by the reviewerNo source consulted states that backswimmers are important forage for fish. The same source describes them eating fish eggs and fry, which is the food web running the other way — worth knowing before you tie one on.
  • Declared by the reviewerNo source consulted describes whether they row with alternating or simultaneous strokes.
  • Sources disagreeHow badly a backswimmer bites differs by source: painful if mishandled in one state field guide, very rare and usually the result of rough handling in a university extension account. Both agree it takes handling.

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.

  • 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.

Carrier reviewed 2026-09-04 · next review due 2026-12-03 · oldest page behind this record read 2026-09-04

Every source in the app, filterable →

Watch the structure

The field marks, moving.

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.

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.

Report an error in Backswimmers →

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