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Hatch MatchHook the Horizon · field intelligence

Observe first · name later

Thirty-nine groups, held to the same standard.

Every entry is built on the reviewed reference set the comparison already uses. No entry claims a current hatch — it tells you what the animal is, what it looks like at each stage, and what it gets mistaken for.

Specimen plate: mayfly nymph in dorsal view showing three tail filaments, plate-like abdominal gills along both sides, and dark wing pads on the thorax.

Ephemeroptera

Mayfly

This one grows wings, and then does it over.

First checkCount the tails, then look for gills along the sides of the abdomen. Three tails plus side gills is about as close to a clean mayfly call as field observation gets.

Specimen plate: caddisfly larva in a portable case of cemented sand grains, with hardened head and legs protruding from the open end.

Trichoptera

Caddisfly

Not every caddis builds a house, and the ones that don't are the ones you miss.

First checkIgnore the case. Look for a hard dark head against a soft pale abdomen, and hooks at the back end.

Specimen plate: stonefly nymph in dorsal view with two tail filaments, two long antennae, and thread-like gills at the thorax rather than along the abdomen.

Plecoptera

Stonefly

Two tails, two antennae, and a poor opinion of swimming.

First checkTwo tails AND two long antennae, with gills at the thorax rather than along the abdomen. Then check whether it can swim — stoneflies mostly cannot.

Specimen plate: midge pupa hanging vertically beneath the surface film with a bulged thorax and a pale feathery gill tuft at the head.

Diptera · Chironomidae

Midge (non-biting)

Small, everywhere, and the reason a dead-looking river isn't.

First checkNo true legs and no long tails. If you see jointed legs or filaments, look somewhere else in the guide.

Specimen plate: hellgrammite, the aquatic larva of a dobsonfly, showing heavy mandibles and eight pairs of lateral filaments down the abdomen.

Megaloptera · Corydalidae

Hellgrammite

Big, armoured, and genuinely able to pinch you back.

First checkSize first. If it is under 25 mm you are almost certainly not looking at a mature hellgrammite. Then check for the row of lateral filaments down both sides.

Specimen plate: freshwater scud or amphipod, a curved translucent side-flattened crustacean with many pairs of walking legs and no insect tails.

Amphipoda · Crustacea — not Insectalook-alike

Scud / Amphipod

Not an insect, not a hatch, and the most common false positive there is.

First checkWatch it swim. On its side means scud, and you can stop there.

Various — not an aquatic hatch order

Terrestrials (ants, beetles, hoppers)

It did not hatch here. It fell.

First checkDid it fall from the bank, or did it come up from the water? If you cannot tell, do not name it a terrestrial.

Osteichthyes — not Insectalook-alike

Baitfish / forage silhouette

If it has fins and a school, stop calling it a bug.

First checkCount fins. If it schools, you are done naming insects.

Odonata

Damselfly / Dragonfly

The mask is the tell. The 'tails' on a damsel nymph are gills.

First checkLook at the mouth. If you can see a grasping mask, you are in Odonata.

Coleoptera

Aquatic beetles

Hard covers, a silver bubble, and no case.

First checkHard wing covers in a dorsal line, or an air bubble under water. If you see a case, look at caddis instead.

BELLY, ENLARGED

Clupeidae (Dorosoma)

Shad (gizzard and threadfin)

Look for the thread, then feel the belly.

First checkIs there a long thread trailing off the back fin? That is the one character in this group that nothing else shares.

EYE VS SNOUTsnout

Clupeidae (Alosa pseudoharengus)

Alewife / river herring

The sawbelly with the oversized eye.

First checkIs the eye wider than the snout is long, with no thread on the back fin? That is alewife rather than shad.

ADIPOSE FIN, ENLARGED

Salmonidae (Coregonus artedi)

Cisco / lake herring

Called a herring, built like a trout.

First checkIs there a small fleshy fin between the back fin and the tail? That is an adipose fin, and it means salmonid, not herring.

No plate is drawn for this group, and that is a decision rather than a backlog item. This family is identified by what is missing — no belly keel, no spines, no adipose fin, no thread off the back fin — so a drawing of one shiner would be asserting a shape the record does not claim for the family. Read the four absences below instead. A plate becomes possible here the day this entry narrows to a named species.

Cyprinidae

Shiners and minnows

One soft fin, smooth belly, nothing else to it.

First checkRun a finger along the belly and look at the front of the back fin. Smooth belly and no spines is a minnow.

TWO FINS, WITH A GAP

Percidae (Perca flavescens)

Yellow perch, young of year

Spines at the front, bars down the side.

First checkTwo separate dorsal fins with a gap between them, and bars rather than a stripe. That is a young perch.

EAR FLAP, ENLARGED

Centrarchidae (Lepomis)

Sunfish, young of year

Deep as a coin, with a dark ear flap.

First checkOne joined dorsal fin and a dark ear flap on a very deep body. That is a sunfish, not a perch.

Decapoda (Cambaridae, Astacidae)

Crayfish

Claws in front, tail fan behind, bottom underneath.

First checkAre there pincers much larger than the walking legs? Then it is a crayfish.

Hirudinea

Leech

A sucker at each end. Nothing else needed.

First checkIs there a sucker at both ends? That is a leech and nothing else.

Oligochaeta (Tubificidae, Naididae)

Aquatic worms

Segments, bristles, no head worth speaking of.

First checkSegmented, round, no legs, no hard head — then look for bristle bundles and check both ends for suckers.

UNDERSIDE — NOTHING THEREno pelvic fin

Ammodytidae

Sand lance (sand eel)

A fish that solves the predator problem by becoming part of the beach.

First checkLook at the underside where the pelvic fins should be. If there is nothing there, and the dorsal runs most of the length of the back, that is a sand lance and you can stop.

TWO DORSALS, GAP BETWEEN

Atherinopsidae

Silversides

The band down the side is the easy part. Count the back fins.

First checkCount the dorsal fins. Two, with a clear gap, on a slim fish with a bright band down the side — silverside. One dorsal — go and look at the anchovy and menhaden entries instead.

SNOUT STANDS IN FRONTjaw sits behind

Engraulidae

Anchovies

You can see through it. That is the character.

First checkCan you see light through the body? One dorsal fin, a big eye and a narrow faint stripe with it, and you are on an anchovy.

SPOTS TRAIL BEHINDnot on herring

Clupeidae (Brevoortia)

Menhaden (bunker, pogy)

Everyone knows the shoulder spot. The shoulder spot is not the answer.

First checkFind the shoulder spot, then look BEHIND it. Rows of smaller spots trailing back is menhaden. A single spot on its own settles nothing.

MOUTH FROM BELOW

Mugil cephalus, Mugil curema

Mullet (young)

Blunt head, small mouth, two back fins, and a habit of leaving the water for no reason anyone can prove.

First checkLook at the head end. Blunt, flat, and a small mouth at the very front, with two widely separated back fins behind it — mullet.

TAIL — ROUNDED, NOT FORKEDeverything else

Fundulus heteroclitus, Fundulus majalis

Killifish (mummichog and striped killifish)

The tail is round. In a marsh creek, that is the whole conversation.

First checkLook at the tail. Rounded or squared off, on a stout fish with a flat head and an upturned mouth, is a killifish. Forked is something else.

HEAD FROM ABOVE

Cottidae

Sculpin

All head and no swim bladder — which is not, on its own, the tell everyone thinks it is.

First checkIs the head clearly wider than the body behind it, with fan-shaped side fins it props itself on? That is a sculpin. Then check for scales — there should not be any.

ROSTRUM — TOOTHED BLADE

Decapoda

Shrimp (grass and penaeid)

Count the clawed legs. Two pairs or three — that is the whole family key.

First checkToothed blade over the eyes, humped back, fan tail. Then count how many front leg pairs carry claws: two is a grass shrimp, three is a penaeid.

GOES IN BACKWARDStail first

Decapoda (Hippidae)

Mole crab (sand flea)

It cannot pinch you. It goes into the sand backwards. It rides waves on purpose.

First checkLook for claws. There are none — anywhere. Add an egg-shaped smooth shell and a pair of feathery antennae and you are holding a mole crab.

APRON, UNDERSIDEmalefemaleyoung

Callinectes sapidus

Blue crab (young)

Twenty-five millimetres across is when it stops hiding in the grass and starts crossing open flats.

First checkCount the spines along one side of the shell and check the back legs. Nine teeth with a long spine at the end, and a rear pair flattened into paddles, is a blue crab.

JAWS — TWO OR FOURclam wormbloodworm

Polychaeta

Marine worms

The short red one swimming at the surface is the same animal as the long brown one in the mud.

First checkLook for the row of leg-like flaps down both sides. Then get the proboscis out if you can: two jaws is a clam worm or sandworm, four is a bloodworm.

Cephalopoda, Loliginidae

Inshore squid

The class this reference has had a name for since v8, and no animal in it until now.

First checkCount the long arms. Eight arms plus two much longer tentacles is a squid; eight and nothing longer is an octopus.

BEAK, NOT JAWSbroad, blunt

Hemiptera (Corixidae)

Water boatmen

Right way up, ruled across the back, and the one aquatic bug that will not bite you.

First checkWhich way up is it swimming? Back uppermost, with dark parallel crosslines across a flat back, is a water boatman.

AT THE SURFACE — SO IS A BEETLE

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.

head, withdrawnTAIL DISC

Diptera (Tipulidae)

Cranefly larvae

A grub with nothing to walk on and a head it keeps to itself.

First checkLook for legs. None at all, on a plump segmented grub, means a fly larva. Then look at the blunt back end for a disc ringed with lobes.

CROSS-SECTIONlies flat, back uppermost

Isopoda (Asellidae)

Aquatic sowbug

It lies flat. A scud falls on its side.

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.

Gastropoda

Freshwater snail

One coiled shell, and a foot out of it.

First checkIs the shell coiled into a spiral, and is what comes out of it a foot rather than a head with legs?

Bivalvia

Clam (small freshwater bivalve)

Two halves and a hinge. That is as far as this goes.

First checkTwo halves with a hinge along the top edge, or one coiled shell?

TAIL: ONE FILAMENTalderfly · hellgrammite

Megaloptera (Sialidae)

Alderfly larva

One filament, straight back. A hellgrammite has two hooks.

First checkLook at the back end. One filament, or two hooks?

currentATTACHMENThooks on a silk pad

Diptera (Simuliidae)

Black fly larva

Bowling pin, gripping the rock, waving downstream.

First checkIs the back end swollen, and is it holding on to the stone with the body standing up in the current?

Before you lose signal

Keep every entry on the phone.

Every reviewed entry, the seasonality read, the patterns and the dossiers, downloaded now and readable with no connection. Nothing is stored until you press it. The whole offline picture is on the log page.

— of —

Checking what is on this device…

Scope of this guide

What a group-level answer is worth.

These are orders and families, not species. A mayfly result means the observation is broadly consistent with Ephemeroptera — it does not name the insect, establish that it is emerging, or say anything about what a fish in front of you is eating. Those are separate questions and this guide does not answer them.

What a group-level call is actually good for is narrowing the field fast, in hand, with cold fingers, without a key. That is the job.