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Colorado's Bug Guide

Colorado's Bug Guide

Matching the hatch becomes easy with this simple look at the bugs that will be swimming, crawling and flying about the Centennial State this summer. (May 2006)

Colorado's rivers and streams share a common heritage in the Rocky Mountains' snowy alpine heights. Over descents that often exceed 9,000 feet, these rocky waterways nurture eight major insect hatches each year -- insects that sustain trout, the No. 1 passion of Colorado anglers.

Flyfishermen hoping to outwit their wily adversary tie thousands of artistic renditions from feathers, fur and artificial components that are designed to emulate these insects. Which fly patterns work best is subject to debate, but anglers who fill their fly boxes with the following patterns can entice trout virtually any day, if they match hatches exactly and present their ties with precision.


Small members of the order Diptera, midges are a year-round trout food. They hatch in huge numbers in winter, spring and fall, and exist in many colors. Mimic them with the following flies on hook sizes 16-24:

Nymphs: Miracle Midge; Mercury Midge Series -- RS II, Black Beauty, Blood Midge.

Emergers: Biot Midge Emerger; CDC Midge Emerger.

Adults: Griffith Gnat; Adams; Black Smut; Biot Midge Adult.



The baetis, or blue-winged olive (BWO), becomes a trout favorite by late February. Trout gorge themselves on baetis from March into May and August into November. These widely distributed, tiny mayflies have an affinity for nasty weather, preferring gloomy, wet days to hatch in profusion, attracting trout to the surface.

Flyfishermen should begin mornings fishing No. 18-22 BWO nymphs in moderate flows and switch to a BWO dun with an emerger dropper when they see the bulges or rises of trout eating emerging or adult bugs. Mimic baetis with the following flies on hook sizes 16-24:

Nymphs: Pheasant Tail (BH and Flashback); Baetis Nymph.

Emergers: CDC Baetis Emerger; Barr's BWO Emerger.

Adults: BWO Comparadun; Parachute BWO.


Pale morning duns (PMDs) hatch from early June to September, and are one of the most important Western hatches for trout. These medium-sized mayflies inhabit slow to rapid-flowing waters in virtually every Colorado stream and river. Hatching normally occurs in slower flows, early in the morning on warm days and as late as afternoon on cool days. Mimic PMDs with the following patterns on hook sizes 14-20:

Nymphs: Pheasant Tail (BH and Flashback); Gold-Ribbed Hare's Ear.

Emergers: Quigley's PMD Cripple; Barr's PMD Emerger.

Adults: Sparkle Dun; Thorax Dun; Parachute PMD; Lt. Cahill; Quill Dun.


Caddis hatch in every stream from spring into fall and attract trout in significant numbers. While the famous Arkansas River Mother's Day hatch attracts anglers from afar, blizzard hatches also occur on many other rivers and streams each spring.

A wide variety of caddis species can make hatches quite complex, but most can be imitated with just a few patterns on hook sizes 12-18:

Larvae: Brassie; Caddis Larva (olive, gray, and tan); Breadcrust.

Pupae: LaFontaine's Sparkle Caddis Pupa; Soft Hackle Partridge and Green, Yellow, and Orange; Deep Sparkle Pupa and Emergent Sparkle Pupa (olive, gray, and tan).

Adults: Elk Hair or Deer Hair Caddis (olive, gray, and tan); X-Caddis; Goddard's Caddis.


Not as widespread as other insects, green drakes hold a special place in flyfishermen's hearts because they draw large trout to the surface. Green drakes are relatively large and easy to see. They hatch while waters clear after spring run-off. Mimic drakes with the following flies on hook sizes 10-12:

Nymphs: Olive Hare's Ear; Green Copper John.

Emergers: Green Drake Emerger; Quigley's Green Drake Cripple.

Adults: A.K.'s Biot Green Drake; Hairwing Green Drake.


The red quill is not widespread, but its patterns can simulate other mayflies. When they do hatch, it's usually at midday on warm days. To mimic them, try the following patterns on hook sizes 12-18:

Nymphs: Pheasant Tail (BH and Flashback); Red Quill Nymph.

Emerger: Red Quill CDC Cripple; Red Quill Quigley Cripple.

Adults: Mahogany Sparkle Dun; Red and Blue Quill Dun/Spinners; Rusty Spinner; Red Quill Spinner.


A four-year lifespan makes several species of stoneflies available all year, making these meaty morsels a major part of a trout's diet. The salmonfly is the largest stone, but its distribution is limited. Little yellow and golden stoneflies are slightly smaller and widely spread. Late in the evenings and at night, stonefly nymphs migrate to shorelines to crawl out of the water prior to emergence, drawing trout into shallow shorelines to feed. Nymph patterns are often more productive than adult flies. Use hook sizes 4-16 to tie these:

Nymphs: Gold-Ribbed Hare's Ear; Kauffman's Stonefly; Halfback.

Adults: Improved Sofa Pillow: Bird's Stonefly (No. 4-8 for Salmonfly); Yellow and Orange Stimulators.


Distribution of the diminutive trico is limited, but they are important to trout wherever they exist, providing food during the hatch and spinner fall. Trico-eating trout can be quite selective because astronomical numbers of tricos blanket the water, lowering the odds that an imitation will be selected instead of a natural. Tie these on size 18-24 hooks:

Nymphs: Pheasant Tail; Trico Nymph.

Emergers: Trico CDC Emerger.

Adults: Trico Poly-Wing Spinner; Trico Comparadun; Trico Sparkle Dun.


The following patterns are successful on most Colorado waters, especially when no hatches are active.

Terrestrials: In late summer into fall, beetles, ants and grasshoppers entice trout as insect hatches diminish. I like them small, 14-18.

Attractors: Royal Wulff; H&L Variant; Humpy (yellow, orange, red) in sizes 14-20.

Nymphs: Copper John (various colors); Prince Nymph; Palomino Midge, in 14-20.

Versatiles: Woolly Bugger (olive, black, purple); Hornberg; Muddler, in 12-16.


The hatch chart reflects conditions throughout Colorado, but not specifically for every river or stream. Variations are described below. For hatch information and specific fly patterns, contact local fly shops or guides.

South Platte -- Home to highly selective trout, the South Platte has no salmonflies; the North, Middle and South Forks have green drakes.

Cache la Poudre -- The Poudre has all major insects except salmonflies. It is prime terrestrial water in late summer/early fall.

Arkansas -- It's famous for the Mother's Day Caddis, but don't forget green drakes, tricos and red quills.

Conejos -- A brown drake substitutes for the green drake here. Leave the trico and salmonfly at home.

Rio Grande -- The mid-June salmonfly hatch is a big event on the middle Rio Grande; no tricos here.

Animas -- The Animas is a caddis river; also popular are golden stones and streamers. There are no tricos, green drakes or red quills.

Gunnison -- The once world-famous salmonfly hatch is now restricted to the river below Blue Mesa Dam; no tricos here.

Colorado -- The Colorado hosts a major salmonfly hatch starting in April; PMDs have a pinkish hue. You won't find green drakes here.

Roaring Fork/Fryingpan -- The Fork's most popular hatches are on both sides of runoff: caddis in April/May, green drakes in July; no salmonflies or tricos. The 'Pan has tricos, but no salmonflies.

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