The comparison scores every group at once. This page is for the moment you already have a pair of names in mind — mayfly or stonefly, scud or sowbug, shad or alewife — and want the structures that keep them apart, in one look. Nothing here is a current hatch.
The differences, and nothing else
Best separating check: No hard head capsule and no legsClose look It separates Aquatic worms from Midge (non-biting) cleanly, and every pair of groups still in play differs on it (look closely with it still).
What to look at
Aquatic worms
Midge (non-biting)
No hard head capsule and no legsdecisiveClose look
Yes
No
Reported size
1–150 mm
2–20 mm
Water it is recorded in
lake margin, river, stream, reservoir
river, stream, lake margin, lake open, spring
Life stages covered
adult
larva, pupa, adult
How it moves
stretching and pulling like an earthworm; waving in the water while anchored in the sediment
wriggling or undulating; anchored by posterior prolegs
Reference seasonality
No family-level window
Emergence: Jan, Feb, Mar, Nov, Dec
Rows come from the reviewed diagnostic weights the comparison scores with. “Decisive” means one answer puts them at least four points apart — the carrier's own rule for a structure that separates a pair.
The two entries, side by side
Oligochaeta (Tubificidae, Naididae)
Aquatic worms
Segments, bristles, no head worth speaking of.
First check
Segmented, round, no legs, no hard head — then look for bristle bundles and check both ends for suckers.
What it is
A soft segmented tube, round in cross section, with no legs and no hardened head. Bundles of fine bristles run along the segments and are the character that separates it from a leech.
Stages
Adult (1–150 mm across the group, most 1–30 mm; tubificids to about 25 mm)
Water
lake-margin, river, stream, reservoir
Separates from Midge (non-biting)
A hard head capsule with prolegs at both ends is a midge larva. Red midge larvae and red worms are both called bloodworms, so the head is the check.
Typical windows
No family-level window in this layer.
Patterns (correspondence)
None mapped yet.
Limits
The regional guide gives 1–30 mm for most aquatic worms and up to 150 mm for the largest; treat the upper figure as the extreme, not the norm.
Small, everywhere, and the reason a dead-looking river isn't.
First check
No true legs and no long tails. If you see jointed legs or filaments, look somewhere else in the guide.
What it is
Chironomidae is enormous — more than 7,300 described species worldwide, found in every kind of water, including salt water. It is also the group most often written off, because everything about it is small.
Stages
Larva (2–20 mm (New Mexico State gives up to 12.5 mm)) · Pupa (No source consulted gives a pupal size) · Adult (2–12 mm)
Water
river, stream, lake-margin, spring
Separates from Aquatic worms
This entry does not name Aquatic worms as a look-alike. That is a gap in the prose, not proof they cannot be confused.
