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Basic Insect Entomology - Artificial Flies

At my first Trout Unlimited meeting they were talking about Mayflies, Blue-Winged Olives, Hendricksons, Duns, Wooly Buggers and many other things involved in catching trout. I thought they were all species of insects; Actually only one, the Hendrickson, was. A Mayfly is an order in the insect class (remember your taxonomy from biology:

Kingdom [animal] < Phylum [arthropod { Insects, Spiders, beetles, ticks, crabs, shrimps, ...}
  < Class [insect] {66-75% of all animal species} < Order [Ephemeroptera (Mayfly)] < Family [Ephemerellidae]
    < Genus [Ephemerella] < Species [Ephemerella subvaria (Hendrickson)].
The name Blue-Winged Olive can refer to a Family Baetidae, a Genus Baetis or Drunella or several species (Baetis tricaudatus, Drunella lata, ...)

A dun is a stage in the mayfly life cycle also a color of some fly tying materials.
A Woolly Bugger is an artificial fly pattern designed to imitate a dobsonfly larva, but used in a variety of situations where fish are feeding on other bait.

From the day that Alfred Ronalds published "The Fly-Fisher's Entomology" in 1836, anglers have been fascinated with aquatic insects and the flies to match them.

This page is a summary so a beginner will have some clue as to what they are talking about, for a excellent site with more complete information see Jason Neuswanger's Aquatic Insects of American Trout Streams at

Insect taxonomic classification:
- Phylum Arthropoda (Arthropods)
  - Class Insecta (Insects)

  Orvis Fly Patterns
Mayflies - Order Ephemeroptera
The Mayfly is the most important group for anglers.
The order Ephemeroptera, or mayflies, comprises 21 families, about 82 genera, and more than 600 species in North America. Of those, there are about 12 families, 30 genera, and a couple of hundred species potentially important to anglers.
Some genus and species in Ephemeroptera:
Brown Duns, Blue-Winged Olives (BWO), Hendricksons, Sulphurs, Hexagenia (Hex) and Big Drakes, Cahills, Quill Gordons, Slate Drakes, Green Drakes, Tricos, Black Quills and Blue Quills, White Flies,

Stages fly Pattern
Nymph Hare's Ear, Pheasant Tail, RS2
Dun1 (Adult) CDC Comparadun BWO, Sparkle Dun
spinner2 AK's Spinner
There are four types of nymphs: Swimmers (Baetidae - BWO), crawlers (Ephemerellidae - Hendricksons, Sulphurs, ..), clingers (Heptageniidae - March Browns, Cahills, Quill Gordons, ..) and burrowers (Ephemeridae - Hexes, Big-Drakes).
1. A dun is the first stage in the adult mayfly's life cycle; usually of short duration (1 to 24 hours); this is the stage most often imitated by the
2. Spinner refers to the stage when the female has dropped back onto the water to die after laying her eggs.
A mayfly spinner (imago) has wings that are hyaline (shiny and transparent).
The Duns will sit on the surface of the water letting their wings dry out in an upright position after emerging. The spinners usually drop their eggs from high then lie on the water usually with their wings prone (or "spent"), and lie motionless on the surface until they are eaten or drowned. See article at orvis.

Hatches: Duns most often emerge during an hour or two each day for a couple weeks sometime in the spring or summer, though there's great variation between species; Slate drakes have multiple generations with hatches thru Sept.. See Hatch Times below.

Caddisflies - Order Trichoptera
Families, Genus and species in Trichoptera:
Early Smoky Wing Sedges, Apple Caddis and Grannoms, Little Black Caddisfly, Little Brown-Green Sedges, Hydropsychidae, Little Brown-Green Sedges, Leptoceridae, Little Black Sedges, Northern Caddisflies, Tiny Black Gold Speckled-Winged Caddis, Green Sedges, Autumn Mottled Sedges, more.

Stage Fly Pattern
Larva Case Caddis, Czech Mate
Emerger SparkleWing Caddis Emerger
Pupa LaFontaine Sparkle Pupa
Adult Elk Wing Caddis
More images below.
Hatches: In the early or mid summer, the larvae reach maturity and move from the faster currents to the slower flows that are generally found along the margins of the stream to begin pupation which takes about 2 months.
It crawls into a protected niche and constructs a cocoon to start pupation. During this period the insect is unavailable as trout food except during catastrophic drifts caused by floods etc.
Most pupae emerge from waters that are too shallow or too exposed for trout.

Stoneflies - Order Plecoptera
Families and genus in Plecoptera:
Little Yellows and Little Greens, Little (Tiny) Black, Roachflies, Golden Stones, Medium Browns and Yellows, Yellow Sally, Salmonflies, Willowflies

Stage Fly Pattern
Nymph Kauffman's Stone
Adult Stimulator
Hatches: They emerge by crawling out of the water onto rocks, sticks, or other shoreline objects.
Order - Diptera (True Flies)
  Family Chironomidae (Midges)

Midges are small, down to hook size 28.

Stage Fly Pattern
Adult Griffith's Gnat, Syl's Midge

Other trout food:
Insects: Alderflies, Beetles, Damselflies, Dobsonflies, Dragonflies, Water Boatmen, Grashoppers
Crustaceans: Crayfish, Scuds, Sowbugs
Fish and amphibians: Minnows, Salamanders
Terrestrials: Insects which live on land and are fed on by trout only when they incidentally fall into the water. Important in late summer. E.g. Order Hymenoptera (Ants, Bees, and Wasps)
I caught a rainbow with an ant at Lola Montez in July.

Life Cycles (Stages):
Insects go thru a metamorphosis transforming into different forms. Stages vary by family. Some examples:

Metamorphosis - Metamorphosis is the change that occurs during the organism's development (life cycle) from egg to adult. Most aquatic insects can be divided into two groups: ones that develop through complete metamorphosis, and ones that develop through incomplete metamorphosis.
Complete metamorphosis, which consists of four stages: Eggs, Larvae, Pupa, Adult. During the pupae stage, which lasts about 2 months, the organisms inhabit a "cocoon-like" structure where the transformation from larvae to adult occurs. They may become completely encrusted with pebbles during this stage. When pupation is complete, the insect which begins the emergence sequence is called a pharate adult It is no longer technically a pupa in the language of entomologists, but anglers refer to it as a pupa.

Examples: Caddisflies, Midge, Mosquitoes, Aquatic Gnats and Flies

Incomplete metamorphosis has three main stages of development (except for the mayfly that has two winged growing stages). These immature insects are called nymphs and they undergo a series of molts until the last decisive molt transforms the organism into an adult or imago in mayflies. There is no intermediate pupae stage where transformation occurs. The nymphs resemble the adults closely except for wing development.
Examples: Mayflies, Stoneflies, Dragonflies
The adult stage of mayflies has two stages:
- dun - first stage < 24 hrs. after emergence.
- From there they molt into a second adult phase called spinners. Their second pair of wings now fully developed, they are also sexually mature. After a few hours or up to a day, they usually , though not always, return to over the water, where they mate, lay their eggs and drop back onto the water to die.
See Life Cycle of Aquatic Insects at

Flies are named by "Fly patterns" designed to imitate insects (in various forms from larva to adult), baitfish, and other fish food.
They can range in size from imitation fish eggs to mice and frogs. There are usually a variety of styles and colors within a given pattern.
They are made with various materials such as bird feathers, animal fur and hair, wool, yarn, foam, beeswax, mylar, ... and are usually held together with sewing thread and glue.

Ernest Schwiebert is credited with popularizing the term "matching the hatch" in 1955.
The theory is trout will go into a feeding frenzy during hatches and only go after dun's, emergers, etc. of the species that is hatching. Some anglers watch for these hatches to decide when to fish. Others claim that if you make a perfect presentation it doesn't matter what fly you use.

When there is no hatch some stick to nymphs because that is what trout are feeding on, others say multi-purpose dry flies will attract fish. There are books written on this and it makes for good discussion.

Gary LaFontaine said that the three main methods of deciding on a particular fly are empiricism (trial and error tempered by previous experience), generalism (actually a denial that fly choice is very important and that fish will take any fly as long as I present it properly.), and naturalism (bug watching).
Source: Unmatching the Hatch, by Mike Lawson

Hatch Times for mid-Atlantic streams:
Number of species with hatches by date:
Dates May-
Caddis Stone
Apr. 15- May 15 13 3 2
May 15- June 15 28 2 2
June 15 - Jul 15 4 0 0
July 15 - Sept 6 0 0
Hatches vary 2 weeks or more from year to year and by location, depending on water temperature.
Some species have multiple generations; e.g. Slate drakes have hatches from April to Sept.
Source: Mid Atlantic Trout Streams and their Hatches by Charles R. Meck
See also: Hatch Charts at Cold Water Fly Fishing for Trout by a volunteer organization.

Selecting a fly is not as simple as matching a pattern to an insect that lands on your arm as in the movie "A River Runs Thru It". Some flying insects only land on the water to die during a short period of time after laying their eggs from the air.

Patterns generally fall into 3 classes: Dry flies (usually imitating adult insects which stay on the top of the water) and 2 classes of wet flies (that sink below the surface of the water), Nymphs/Emergers and Streamers/Poppers/Terrestrials.
- Dave Hughes book, Trout Flies: The Tier's Reference gives two generic types:
searching flies (attracters), for those time when trout are feeding non-selectively, and imitative flies (naturals), when trout are taking a specific food form and nothing else. Imitative flies are most effective in slow-moving, clear water, with finicky trout in fertile streams with large populations of aquatic insects. lists the following types: Dry Flies, Hoppers, May Flies, Parachutes, Nymphs, Beadheads, Wet Flies, Streamers, Muddlers, Salmon, Bass Bugs, Deceivers. See terms below.

Most popular flies:
(Number of selections) out of 8 by "Experts' Top Ten" at
10 Best Trout Flies at

Woolly Bugger (5) (streamer):
Tied to imitate the Dobsonfly larva, leeches, baitfish (minnows, night crawlers, ...), tadpoles, damselfly larvae, dragonfly larvae, crayfish and others.
A generalist pattern that's always worth a try and a must have for any fly box, dry fly purists excepted!

In this 'original' dressing the pattern can be used for trout, largemouth and smallmouth bass, panfish, chub, and carp, to name a few. In suitable sizes and with more applicable colors you can expect to get into steelhead, salmon, stripers and more.

Pheasant Tail (4) (Nymph)

Mayflies, Midges, and Stoneflies

Hare's Ear (4) (Nymph)

Mayflies, Caddis, Stoneflies

Elk-Hair Caddis (4) (Dry fly)

Meant to imitate a fluttering adult caddis, though it will also work as a spent adult. Looking not unlike a stonefly, cricket, even a small hopper.

Adams (4) (Dry fly)

Used in its smaller sizes to cover midge hatches and mayfly hatches. In the right size it makes a reasonable impression of a blue winged olive (BWO) or other small grey/olive bodied mayfly. Larger versions are serviceable in a drake hatch.

- Partridge Soft Hackles
Actually more of a style of fly than a specific pattern.

- Midges and Chironomids
Term often used by lake anglers, are the smallest insects flyfishers commonly try to imitate.

Griffith's Gnat (3) (Dry Fly, Emerger)

This fly excels when midges are hatching and mating on all types of water.

Clouser Minnow (3) (streamer)
Primarily a saltwater fly effective on nearly every predatory saltwater species. It has also become a very popular freshwater streamer pattern, especially on the west coast. They are very versatile, impressionistic flies. They can imitate everything from an ascending caddisfly pupa to a drowned mayfly to a Yellow Sally stonefly.

Muddler Minnow (streamer)
The Muddler Minnow is one of the most versatile and effective flies ever conceived. Originally designed to represent a species of bottom-hugging sculpin in Lake Superior tributaries. Muddler is also a fine grasshopper pattern.

Other popular flies: Light Cahill, Royal Coachman
Purchase Flies:,, DiscountFlies Online Fly Shop, Discount Flies at,,, Orvis
Continental Flies Trout Dry Fly Assortment

  • AK - A.K. Best is one of the most well-known and innovative fly tiers in the world.
    AK's Spinner - An absolutely killing fly when fished during falls of E.ignita spinners in July (European blue-winged olives)
  • Beadheads - A type of nymph fly typically with a brass bead which helps keep the fly very close to the bottom where trout are used to seeing and capturing naturals. Hares Ears and Pheasant Tails (above) are beadheads.
  • Broods: When a species produces more than one generation per year, each one is called a brood.
  • BWO - Blue winged Olive. Several genus and species of Mayfly, most frequently the baetis. Tied as nymphs, emergers and dry flies. They have different sizes, colors, and behaviors.
  • CDC - stands for "Cul de Canard" which literally translates to "butt of the duck". Used both to refer to the feathers from the area around the oil gland of a duck and also to the flies tied with these feathers. The feathers from this area are very wispy and impregnated with natural oils making them extremely waterproof. Orvis CDC Comparadun BWO
  • Deceivers - The deceiver pattern is one of the best known and oldest fly patterns in saltwater fly fishing used to imitate different bait fish. Most recently, freshwater fisherman have begun using "tiny" deceivers for trout. Clousers (above) are a type of deceiver.
  • Dry Fly - any fly fished upon the surface of the water; usually constructed of non-water-absorbent materials; most commonly used to imitate the adult stage of aquatic insects.
  • Dun - (1) first stage in the adult mayfly's life cycle; usually of short duration (1 to 24 hours); this is the stage most often imitated by the dry fly; They then molt into the spinner (imago) stage, in which they mate and die.
    (2) A darkish gray-blue color that is very desirable in some fly tying materials.
  • Emerger - pertaining to aquatic insects, the name used to describe that time frame when the nymph reaches the surface and the adult hatches out; the emerging nymph may well be the single most important nymph phase for the fly fishers to imitate.
  • Hackle - A feather, usually from the neck area of a chicken; can be any color (dyed or natural); hackle quality, such as the stiffness of the individual fibers and amount of web, determines the type of fly tied with the hackle; many hackles are grown specifically for fly tying.
  • Hatch - The time when a large number of nymphs or pupas become fully winged flies, often producing frantic feeding activity among trout.
  • Hollow Hair - hair from some animals is mostly hollow, thus holding air and making these hairs float. Ideal for tying dry flies and bass bugs. Antelope, deer, and elk all have hollow hair.
  • Hoppers - Grasshopper flies.
  • Instar: Many invertebrates molt through dozens of progressively larger and better-developed stages as they grow. Each of these stages is known as an instar. Hard-bodied nymphs typically molt through more instars than soft-bodied larvae.
  • Larva - Many classes of aquatic insects, such as caddisflies, midges, craneflies, dobsonflies, alderflies, and many more, are known as "larvae" rather than "nymphs" in their juvenile stages. They have mostly soft bodies rather than hard exoskeletons. These insects also advance through a "pupa" stage before reaching adulthood. Many species of caddis larva build a protective covering of fine gravel or debris to protect them in this stage. The larva is a bottom dwelling non-swimming stage of the insect.
  • Metamorphosis - Metamorphosis is the change that occurs during the organism's development (life cycle) from egg to adult. See Life Cycle above.
  • Midge - a term properly applied to the small Dipterans that trout feed on. Many people call them gnats.
  • Muddler - A type of streamer fly that typically imitates Sculpins or juvenile bullhead catfish.
  • Nymphs: The juvenile, underwater stages of mayflies, stoneflies, dragonflies, and damselflies and other aquatic insects whose juvenile stages are covered by hard exoskeletons. 90% of the time fish feeding takes place below the surface on nymphs. The word can also refer to the fishing flies which imitate these creatures, in which case it is used as a blanket term for flies imitating any underwater stage of an invertebrate (except for crayfish and leeches).
  • Nymphing - word describing fish feeding on nymphs; nymphing right at the surface can be difficult to tell from fish feeding on adults, careful observation should tell.
  • Parachute - A type of dry fly where the hackle is wound horizontally around the base of the wing like a parachute instead of vertically around the hook of the fly. This drops the body of the fly down into the surface film of the water. It is usually most effective in medium to slow moving waters.
  • PMD - Pale morning dun
  • Popper - A bass bug made from a hard material. Usually cork or balsa wood, as these are high floating materials that can be made into a variety of shapes.
  • Pupa - In insects, the transition stage between the larva and the adult; to fly-fishers, caddis pupa are the most important of these insects.
  • RS2 - Rim's Semblance #2 The famous mayfly nymph pattern invented by Rim Chung. See RS2 at
  • Shuck - The shed exoskeleton left over when an insect molts into its next stage or instar. Most often it describes the last nymphal or pupal skin exited during emergence into a winged adult.).
  • Spent - The wing position of many aquatic insects when they fall on the water after mating. The wings of both sides lay flat on the water. The word may be used to describe insects with their wings in that position, as well as the position itself.
  • Spinner - The egg laying stage of the mayfly; overall not as important to the fly fisher as the dun stage; (see mayfly and dun).
  • Streamer - fly tied to imitate the various species of baitfish upon which game fish feed; usually tied using feathers for the wing, but can be tied with hair and/or feathers; tied in all sizes.
  • Sternites - The bottom (ventral) part of a single segment on an insect's abdomen.
  • Turbinate - Shaped like a top or elevated on a stalk; usually refers to the eyes of some adult male Baetidae mayflies which are wider near the tip than at the base.
  • Terrestrial - A terrestrial fly is a fly tied to imitate a ground insect that has fallen in the water or has drowned. Prime examples of terrestrial flies include the ant, beetle, cicada, cricket, and grasshopper. Terrestrials can make up more than 60% of a fish's diet at certain times of the year in late summer and early fall.
  • Wet Fly - (1) any fly fished below the surface of the water; nymphs and streamers are wet flies.
    (2) A traditional style of fly tied with soft, swept back hackle, and a backward sweeping wing; the forerunner of the nymph and streamer.
  • Wing pads - A protrusion from the thorax of an insect nymph which holds the developing wings. Black wing pads usually indicate that the nymph is nearly ready to emerge into an adult.
See: Fly Fishing Terms at Orvis
Trout Flies: The Tier's Reference by Dave Hughes
Haandbook of Hatches by Dave Hughes
Essential Trout Flies, by Dave Hughes
The Benchside Introduction to Fly Tying by Ted Leeson and Jim Schollmeyer

Best fly fishing places
Aquatic Insects of American Trout Streams at Jason Neuswanger's
Bug Basics at
Insect Illustrations at
Flytier's Page, by Hans Weilenmann
Entomology at
Aquatic macro invertebrates commonly found in the streams and rivers of Southeastern Ohio. by Jean V. D'sa
Fly Patterns at
Patterns at
Rise Form Studio NJ and W. PA fly fishing videos and information by John Collins and Mike McAuliffe
How fishing fly is made
Fly Fishing Terms at: Orvis | An International Glossary Of Fly Fishing Terms

last updated 7 May 2009