Streamside Entomology: A Practical Guide

You don’t need a PhD in entomology to catch fish. A practical understanding of aquatic insects is all you need.

The Simplified Approach

Most anglers need to recognize:

• Mayflies (upright wings)
• Caddisflies (tent-shaped wings)
• Stoneflies (folded wings, large)
• Midges (tiny, mosquito-like)

That’s it. Four insect groups. Everything else is details.

Quick Identification Guide

On the Water

Flying over water:

• Mayflies: Sailboat-like, flutter, float
• Caddis: Erratic, darting flight
• Stoneflies: Awkward, floppy flight
• Midges: Mosquito-like, swarm

On the water surface:

• Mayflies: Upright wings like sailboats
• Caddis: Tent-shaped wings
• Stoneflies: Laid flat on water
• Midges: Tiny, barely visible

On streamside rocks:

• Mayfly nymphs: Three tails, plate-like gills
• Caddis larvae: Cases or stick protruding
• Stonefly nymphs: Two tails, feathery gills
• Midge larvae: Tiny red worms

The Carrying System

Essential Tools

Small bug seine:

• Frame with fine mesh
• Hold in current to catch drifting insects
• See what trout are eating
• Fits in vest pocket

Small container:

• collecting jar
• Magnifier (optional)
• Compare to fly box

Small note pad:

• Record what you observe
• Note sizes, colors
• Remember successful patterns

The Bug Seine Method

1. Place seine in current
2. Disturb upstream rocks
3. Collect insects in seine
4. Examine what you found
5. Match with your patterns

Quick Size Reference

Mayflies

Large (Size 8-12):

• March Browns
• Green Drakes
• Brown Drakes
• Golden Stones

Medium (Size 12-16):

• Blue-winged Olives
• Pale Morning Duns
• Hendricksons
• Cahills

Small (Size 16-20):

• Tricos
• Small BWOs
• Mahogany Duns

Tiny (Size 20-28):

• Midges
• Tricos (smaller ones)
• Tiny BWOs

Caddisflies

Sizes 10-14:

• October Caddis
• Mother’s Day Caddis
• Large sedges

Sizes 14-18:

• Most caddis species
• Elk Hair Caddis range
• Most common sizes

Stoneflies

Sizes 4-8:

• Salmonflies
• Large golden stones

Sizes 8-12:

• Golden stones
• Yellow sallies

Midges

Sizes 18-28:

• Tiny to very tiny
• Most common: 20-24

Color Coding

Mayfly Colors

Olive/gray:

• Blue-winged Olives
• Most common mayfly

Tan/gray:

• Pale Morning Duns
• Cahills

Brown/gray:

• March Browns
• Hendricksons

Yellow/green:

• Green Drakes
• Pale Evening Duns

Black/cream:

• Tricos

Caddis Colors

Tan/olive:

• Most common caddis
• Elk Hair Caddis color

Olive:

• Hydropsyche species

Black/dark gray:

• Little black caddis
• Grannoms

Orange:

• October Caddis

Seasonal Hatch Chart

Spring (March-May)

Summer (June-August)

Fall (September-November)

Winter (December-February)

The Three Questions

When you’re on the water, answer three questions:

1. What Are They Eating?

Check:

• Rising fish (what stage?)
• Streamside rocks (turn them over)
• Air above water (flying insects)
• Spider webs (catch insects)
• Seine the water

2. What Size?

Check:

• Catch an insect if you can
• Compare to hook sizes
• Match exactly if possible
• Size is most important

3. What Stage?

Check:

• Are fish rising to duns?
• Refusing duns? Try emergers
• Subtle rises? Try spinners
• No rises? Fish nymphs

Simplified Matching

Mayfly System

Carry these patterns:

Nymphs:

• Pheasant Tail: 14-20
• Hare’s Ear: 12-18
• Copper John: 14-20

Duns:

• Adams Parachute: 12-18
• Comparaduns: Various colors
• Sparkle Duns: Various colors

Emergers:

• RS2: 16-22
• Barr’s Emerger: 14-20

Spinners:

• Rusty Spinner: 14-22
• CDC Spinners: Various colors

Caddis System

Carry these patterns:

Larvae:

• Green Rock Worm: 12-16

Pupae:

• Sparkle Pupa: 12-18 (olive, tan)
• Soft Hackle: 14-18

Adults:

• Elk Hair Caddis: 12-18 (tan, olive, black)
• X-Caddis: 14-18

Midge System

Carry these patterns:

Larvae/Pupae:

• Zebra Midge: 18-24 (black, red)
• Miracle Nymph: 18-22

Adults:

• Griffith’s Gnat: 18-22
• Midge Cluster: 16-20

The 80/20 Rule

20% of the patterns catch 80% of the fish:

Nymphs:

• Pheasant Tail (16-18)
• Hare’s Ear (14-16)
• Prince Nymph (12-14)
• Copper John (16-18)
• Zebra Midge (20-22)

Dries:

• Adams Parachute (14-16)
• Elk Hair Caddis (14-16)
• Royal Wulff (12-14)
• Griffith’s Gnat (20-22)

Streamers:

• Woolly Bugger (6-10)
• Clouser Minnow (6-10)

Learning Resources

Carry

• Small bug seine
• Basic fly box
• Notepad
• Forceps (for examining insects)

Practice

• Stop and observe
• Catch insects
• Compare to flies
• Record what works

Learn

• Local fly shop reports
• Online hatch charts
• Guide recommendations
• Other anglers

Common Mistakes

Over-complicating:

• Don’t need to know exact species
• General categories work fine
• Size matters most

Not observing:

• Don’t just cast blindly
• Look around first
• What are fish eating?

Carrying too much:

• Patterns you never use
• Every size of every pattern
• Simplify and focus

The Practical Approach

1. Observe first: Spend 5 minutes watching
2. Match size: Most important factor
3. Match profile: Upright vs. tent wings
4. Match color: Third priority
5. Match stage: Nymph, emerger, dun, spinner
6. Present well: More important than perfect imitation

Confidence Patterns

When in doubt, fish:

Nymphing:

• Hare’s Ear (14-16)
• Pheasant Tail (16-18)
• Prince (12-14)

Dry fly:

• Adams Parachute (14-16)
• Elk Hair Caddis (14-16)

Don’t worry:

• These work when nothing else is hatching
• Fish aren’t always selective
• Presentation beats pattern

The Journey

Entomology knowledge accumulates over time:

• Every trip teaches you something
• Take notes, remember successful patterns
• Ask questions
• Observe carefully
• Stay curious

You don’t need to be an expert. You just need to be observant and willing to learn.

The best fly fishers aren’t necessarily the best entomologists. They’re the best observers and the most adaptable.

Keep it simple, observe carefully, and you’ll catch more fish.