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Entomology Basics

 

Brief and basic foundation for understanding the insects that trout eat.

The Very Basics of Fly Fishing Entomology Image

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Wallace Westfeldt - April 1, 2008

This article is not intended to be a substitute for infinitely better articles, books, and pictures on this subject. Rather, it is intended to be the briefest basic foundation for understanding the insects that trout eat. Beginning anglers or experienced ones who are starting to learn the entomology may find this useful as a starting point. The pictures of the naturals are only single examples not intended to be representative of all varieties. Likewise, the imitation examples are not suggestions of what to use. Specific conditions, experience, and luck will help you select the right imitation for the specific situation.

INTRODUCTION:

When it comes to imitating insects, the fly fishing angler is interested in five types: Mayflies, Caddisflies, Stoneflies, Midges, and Terrestrials. The Terrestrials that are of primary interest are hoppers, beetles, and ants. Imitations of these are usually fished on the surface. If you see the naturals around, this is frequently an effective choice, particularly presented near banks, shorelines, or bushes. This article focuses on the aquatic insects.
AQUATIC INSECTS:
Throughout the year, Trout feed on different kinds of aquatic insects. Most of that feeding is subsurface. All of these insects have life cycle that consists of the egg, one or two forms of pre-adult, and one or two forms of adult stages. Adults mate and females bring the eggs back to the water. The egg stage is not discussed here. Bear in mind that the transition from pre-adult into adult (called emergence) is of particular interest because that is when the insect is most vulnerable and therefore a primary feeding target for trout.
IMITATIONS:
The fly patterns anglers use to imitate the natural insects vary from the realistic to abstract impressions. There are many patterns that serve two or more insect varieties as well as patterns that are designed to attract rather than imitate. There is much study and debate (scientific and otherwise) as to which patterns to use and why they work. Consult your local flyshop/guide for what’s working in local waters. Several beers have been known to create much confidence should you desire to enter in the debate. When working solo, use the generalization (to which there are many successful exceptions) Size, Shape, Color. In other words, select a pattern that appears to match what the trout are feeding on, first by size, then shape, and then color. Bear in mind that the correct pattern presented incorrectly will fail much of the time.
MAYFLIES
Order: Ephemeroptera

 

Life Cycle
Identifiers
Natural
Imitation
Nymph
Usually 3 tails sometimes 2, single large wingcase, hair or paddle-like gills on abdomen
Baetidae, (Blue-Wing Olive)
 
 
BH Flashback Pheasant Tail
Dun
Two large upright wings (looks like small sails on water)colored, pair of small insignificant wings, 2 or 3 tails
Baetis, (Blue-Wing Olive)
Adams
Spinner
Wings are translucent. Spent spinners fall back onto the water with wings splayed flat.
Trico Spinner
Trico Spinner

 

*For the best pictures and explanations of naturals go to www.troutnut.com
NOTES:
1. The emergence phase of MayFlies is one of the most efficient feeding times for trout. Therefore, there are numerous “emergence” imitations designed to float lower on the water, in the surface film, or just below the surface film. One of the most popular of these imitations is the Parachute Adams which has a horizontal hackle instead of the vertical one shown in the table above.
Parachute Adams
2. Once the Dun leaves the water, it molts into a Spinner. Spinners mate, lay eggs, and then fall spent onto the water (Spinner Fall).
3. Tricos are very small mayflies (#22). Fishing the Trico Hatch and the subsequent Spinner Fall is great fun, but requires special techniques. Ask for advice for this hatch.
 
CADDISFLIES
Order: Tricoptera

 

Life Cycle
Identifiers
Natural
Imitation
Larva (uncased)
Green worms. Bright green, dark olive.
Uncased
Electric Caddis
Larva (cased)
Green worms in tubular or stone cases.
Stone Case
Case Caddis
Pupa
Small versions of the emerging pods from the original version of “Invasion of the Body Snatchers”
Sedge Pupa
Emerging Sparkle Pupa
Adult
Long low wings extending beyond body like a tent or inverted V. No tails. Long antennae
Brachycentrus
Elk Hair Caddis

 

*For the best pictures and explanations of naturals go to www.troutnut.com
NOTES:
1. Caddis pupae fill their sheaths with gas bubbles and float to the surface. This is prime feeding time for adults.
2. Adult caddis can be very active on the surface. Twitching the fly will often instigate a strike.
STONEFLIES
Order: Plecoptera

 

Life Cycle
Identifiers
Natural
Imitation
Nymph
Flat, two short tails, two antennae, two equal wing cases. Most stoneflies are large.
Golden Stone Nymph
Pat's Rubber Leg, Girdle
Adult
Four long wings laying flat across the body when at rest. Two tails
Golden Stone Adult
Stimulator

 

*For the best pictures and explanations of naturals go to www.troutnut.com
NOTES:
1. Found in fast, cool, rocky streams.
2. Nymphs crawl out on land before molting into adults. Look for empty shucks on streamside rocks.
3. Check out the times for your local Salmon Fly hatch and carry a few, in case you get lucky.
 
MIDGES
Order: Diptera(True Flies) Family: Chironomidae

 

Life Cycle
Identifiers
Natural
Imitation
Larva
Skinny, no bulbous thorax.
Larva
Red Thread Midge
Pupa
Skinny profile, bulbous thorax. Black, olive, tan, red, gray, cream.
Pupa
Zebra Midge
Adult
Wings flat and tight across body. Shorter than body. No tail
Adult
Griffths Gnat

 

*For the best pictures and explanations of naturals go to www.troutnut.com
NOTES:
1. Midges are available all year long, which means they are usually the preferred winter hatch.
2. They are frequently small and dry fly fishing with midges can be quite challenging. Trout seem to be selective about the size of adult midges.
3. Having a midge pupa or larva as part of multifly rig is quite common in tailwater.
ImageWallace Westfeldt
303 601-1902
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www.mudbugco.com

Last Updated (Friday, 19 November 2010 13:42)