Hidden Lakes press

Hidden Lakes Press

Information for Recreation in Colorado and the Rockies

Colorado's Bugs Of Summer

© Al Marlowe

For the fly fisherman hitting the peak of a hatch is what trout fishing is all about. It's the equivalent of a hunter taking a trophy buck, or a skier schussing through a foot of fresh powder.

Anglers who are not regular fly fishermen may not be aware of it but Colorado waters offer a hatch somewhere year round. No doubt the hatches of summer present the most pleasant fishing conditions.

Before getting into the specifics of the a few hatches it may be well to first consider tackle. With a few exceptions aquatic insects are generally small. Most are imitated on hook sizes ranging from No. 14 down to No. 22, and even smaller. This means that light leaders are needed with tippet sizes tapering down to 5x or 6x. Length should run from a minimum of nine feet to as long as 12.

The use of fluorocarbon tippets is becoming more common among successful anglers since it has a refractive index close to that of water, meaning it becomes nearly invisible to the fish. A light rod of 3- or 4-weight is an excellent choice for fishing most hatches. A good cane rod is also a great choice for such fishing. Their typically soft, slow actions put less strain on the tippet and as an additional bonus, make it easy to gently place the fly on the water without a fish-spooking splash.

Fishing with light tippets and hooking a trout of 16 inches or more means a reel with a smooth drag is essential. It doesn't necessarily require an expensive reel, though. There are still lots of anglers who fish with the old reliable Pflueger Medalist and do just fine with it.


The mother of all hatches is probably the Mother's Day caddis hatch on the Arkansas River from Salida downstream. This one usually begins in April, reaches a peak in the first half of May, and continues through the summer.

Although there are likely several varieties of caddis on the Arkansas it's not critical to know each one. What is important is to have a good selection of sizes and colors in your fly box. Recommended patterns include the Elk Hair Caddis in gray, tan, and olive in sizes 12 to 18, Black Elk Hair Caddis in 14 to 18, and the Goddard Caddis in 12 to- 16. The Stimulator is a good searching pattern.

Just because there are caddis on the surface don't always assume that the fish want the adults. Depending on the stage of the hatch the trout may concentrate on larvae or emergers. Fish it by casting across stream with a bit of weight. Allow the fly to be carried by the current until it rises at the end of the drift.

Spring caddis hatches also occur on the Roaring Fork and Colorado River in the Glenwood Springs area. An emerger pattern that works well here is the Prince Nymph. Throughout the spring and summer, though, caddis will be available to trout. Come to think of it, there aren't many waters in Colorado where a caddis imitation won't take trout.

Giant Stonefly

The good news about this hatch, commonly referred to as the Willow Fly, is that the trout love it. The bad news is that it usually coincides with runoff. The trout don't care but high water of June and even into early July does present some difficulties.

Fishing this hatch is the time to switch to a heavier rod. With streams running high and fast a long cast can get your fly to a good spot easier. Along with longer casts the flies imitating the adults run large. Recommended size for the Sofa Pillow is 4 to 8. Big flies are quite wind resistant and can be cast easier using a rod of 6-weight and heavier. Heavier tippets, 3x or 4x, are needed to handle the large patterns. Other patterns to imitate the adults include the Stimulator and Fluttering Orange Stonefly, all in sizes 4 through 8.

The Colorado River is one of the premier stonefly streams, from Middle Park, and on down to Rifle. The stretch between Granby and Kremmling is the easiest to fish during runoff. Downstream from Gore Canyon the river is large. If you fish this section work close to shore. Use caution when boating, especially when flows exceed 3,000 cfs.

The stones begin hatching as early as April in Middle Park. When the adults don't draw interest from trout, tie on a nymph. Two patterns that work well here are the Halfback and 20-incher, both on hooks size 4 to 8. The stoneflies may continue hatching through August but are usually a bit sparse by then. It's still worthwhile to tie on a big Sofa Pillow, however, as the fish will continue to go for a large morsel even when the adults are seen much less frequently.

Other rivers with notable stonefly hatches in Colorado are the Roaring Fork, Gunnison, and Rio Grande. The timing of the hatch varies some but all will have action on either adults or nymphs

Green Drake

Green Drakes are some of the larger mayflies. Adults are imitated with dry-fly patterns sizes 10 and 12. As on other rivers, this one begins on the lower stretches and progresses upstream through the summer. Although the Drakes are large, it won't hurt to tie on a little smaller fly, particularly if trout inspect but reject your offering.

The hatch normally begins in July and Drakes continue to emerge through September. The peak is shortly after it starts and by late summer the Drakes are fewer in number.

Stream flows are usually low and clear for the hatch, making wading easy in most rivers. While the hatch is a mid-morning to mid-afternoon event, anglers will be able to take trout before it gets going good using emerger patterns. Use a small amount of weight on the leader and a strike indicator. In the clear water trout may be observed swimming actively in the pools. If they're not rising, take the hint and use emergers. Be prepared to switch to dries when trout begin taking the adults.


This tiny mayfly hatches beginning in July or August and continues through October. It's not a widespread hatch like other mayflies. The main rivers to fish tricos are the South Platte, Colorado, and Fryingpan. Tie on a Parachute Adams in 18 to 22 to imitate adults. Late in the day, after the adults have mated, they die and fall to the water. For this stage a No. 20 or 22 Trico Spinner gets action. Use a No. 18 to 22 Pheasant Tail to imitate the nymphs or emergers.


These minute insects are found about everywhere. On some waters they are seasonal. On others they are around all the time. Midges live at all elevations, too, so they hatch on high lakes. Probably the most frequently used imitation is the Griffith's Gnat. Keep it small, sizes 18 through 22. The same sizes of Adams work well, too. To imitate emergers try the Brassie, black or olive Palomino Midge, or Pheasant Tail.


By August some lakes and streams, particularly those other than tailwaters, run low and water temperatures rise. Insect hatches tend to occur early and late in the day then. Trout still have to eat, though, and terrestrial insects provide action at that time.

Quite often grasshoppers hanging out near the water's edge fall into the stream or lake, creating an artificial "hatch." Being poor swimmers they create fish-attracting commotion as they struggle for safety. Cast a hopper pattern close to the bank. Let it land with a splash and twitch it to suggest a struggling insect.

Ants are to trout what chocolate is to a chocaholic – irresistible. These insects also get into the water by accident. As with hoppers, work the fly close to the bank.

Beatles are a gourmet meal for trout. These important sources of protein are common in Colorado but are probably under-utilized by anglers. Beatles come in a variety of sizes, shapes, and colors, as should imitations in your fly box.

Although not every insect is discussed, these are some of the major hatches of summer and early fall. Stock your fly boxes with an assortment of patterns so you'll be ready when the trout are feeding fast and furious. With a bit of planning, you'll enjoy these hatches at their peak.