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.

MIDGES
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.

BAETIS
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
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
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.