One of the aspects of fly fishing that has anglers scratching their heads is trying to better understand and identify the insects that play such a crucial role in a trout’s diet here in Colorado and throughout the west.

As anglers we often hear the phrase “Match the hatch”, in reality budding anglers tend to experience information overload which often leads to frustration and they loose some of their new found passion and ask themselves “Man, there is so much to learn, how am I ever going to get my head around this and retain all of the nuances of fly fishing”? We’ll the good news is we’ve all been there. One of the best attributes about fly fishing, and there are many, is you never stop learning, EVER!

The best advice we can pass along is to keep it simple! All too often we over-think the process of fly identification and fly selection. No need to go into a master’s level course in entomology (I couldn’t teach one if I had to), better to concentrate on a more simplistic approach – SIZE, SHAPE, and COLOR when trying to “Match a hatch”

Simply put, if you have box of flies and no clue as to what to use, spend 5minutes or so doing nothing but taking in your surrounding environment. Do you see any insects? If so, what size shape and color are they? Are you seeing fish rising? You get the idea…Fly fishing success depends largely on our visual acuity. You set the hook when you see a fish eat your dry fly, you set when your indicator goes upstream. Take a similar approach when selecting your flies. In most cases, trout are constantly telling us what they are eating each day. We just have to take the time to look at our surroundings and under a few rocks in the river now and again.

Common Hatches



Easy to identify, Mayflies have a transparent wing post that looks like a sailboat. Most Mayfly patterns can be imitated with the same pattern just by using different sizes and colors. Common Mayflies throughout Colorado include Blue Wing Olive (BWO), Pale Morning Dun (PMD), Drakes (green and grey), Quills (red & brown) and Tricos. After spending most of its life underwater as a nymph, a mayfly swims to the surface to hatch. During this swim up (emerger stage) the emerger hatches into a dun, which while on the surface is a primary food source for trout. The dun then flies off the water to nearby foliage where it undergoes another transformation. At this point, it becomes a spinner, which will join others and be seen swarming over the surface in mating flights. Some spinners will drop their fertilized eggs, others will touch down on the surface to deposit their eggs. With the act of renewing the species complete, the spinners fall to the surface to be eaten in great numbers by the trout.


Mayflies are a viable food source from March through October, with BWO's being a Spring and Fall hatch, and other mayflies coming more during the summer months


2 or 3 tails, 1 wing pad, plate-like gills found on the abdomen segments only, classified into 4 groups: crawlers, swimmers, burrowers and clingers


2 or 3 long tails, wings held up vertically, the body is slender and delicate, duns identified by gray opaque wings, spinners identified by transparent wings


Very abundant in Colorado, the Caddis fly can tolerate all types of water conditions, although they tend to prefer cool clean water (hence their love of Colorado). Caddis are one of the more abundant stream-bottom insects, to the point where they can produce prolific hatches, where insects literally "blanket" the river banks and shores. The caddis fly begins its life in an egg, and after the egg stage the insect spends most of its life in the larva stage, where it is encased in a protective shell it manufacturers either of small sticks or pieces of gravel. When its ready to hatch, the caddis swims up as a pupa, and rides on the flow of the river where it may be taken by a feeding fish if it doesn't escape to a nearby shore as an adult. When adults have mated, some deposit their eggs on the surface of the river, while others will swim to the bottom to deposit their eggs, and then swim to the surface again. It is these diving caddis that anglers frequently confuse with hatching caddis.


Caddis are resilient insects, that are typically present from early April through October


Small antennae, no tail, some are case builders, others free living


Antennae the length of body, no tail


4 well-developed wings, no tails, antennae the length of body


The Stonefly also referred to as a Salmon Fly or Willow Fly, is a staple food source for Trouts across the state of Colorado. This insect is unique in that it only has 2 life cycles, the nymphal stage, and the adult stage. Once hatched, the stonefly nymph crawls along the bottom of the river and will crawl towards the river's edge, as opposed to other insects who go through an emerger state. The life-cycle of a stonefly nymph is 1-3 years, during which time they are prime suspects for a trout's diet. Stoneflies are often considered to be a primitive insect, and are easily recognizable by their size, as they are the largest of the aquatic insects. Their presence in a stream or still water is usually an indicator of good or excellent water quality with healthy oxygen levels.


Stoneflies are available food sources 365 days a year, although they are predominantly a Spring, Summer and Fall hatch.

Nymph Stage Characteristics

2 Heavy Tails, 2 antennae, 2 wing pads, gills absent

Adult Stage Characteristics

2 tails (short or long), long stout antennae, 4 wings of equal length, wings normally longer than the abdomen.


A small two-winged insect group found in virtually every freshwater environment. Midges are a year-round insect, where they play an important role in a trout’s diet, especially during the winter months when rivers are nearly void of insect life. While they are commonly present on most fishable trout water, they are incredibly small with the most effective sizes being between size 18 and size 24. With that said, on lake and still water environments you may see arger sizes 10 – 14’s for still water fishing. Grey, red and black is always great color choices.


Midges are an available food source 365 days a year


no tail, small antennae (if at all), no leg and body looks like a segmented tube, colors include: tan, brown, green, red, black


Head, thorax and wings are clumped together, no tail, pupal color same as larva color


Males have fuzzy antennae, slender body and wings, very small in size


Terrestrials, or land-based insects, are another staple in diets of trout. Terrestrials include grasshoppers, crickets, ants, beetles, and just about any other bug that might get knocked down into the water. Although not "hatching" insects, terrestrials make up a significant portion of a trout's diet. On many western streams, using a grasshopper during the summer months can create a memorable fishing experience.

Eggs & Worms

Eggs & Worms

Like terrestrials, Eggs and Worms are not hatching insect, or even insects at all. But they are an important food source, as they are very high in protein and offer substantial substance in a small package. Worms can be found in most any freshwater environment, and are great to fish during our after rising water levels. Eggs will be available during spawning periods in the spring (rainbow and cutthroat spawn) and fall (brown trout, kokanee and brook trout spawn.

On your next visit to the river, leave your fly rod in the car for a half hour or so. Spend some time just observing your environment. You’ll be amazed at what you see and learn. And most importantly, trout don’t speak Latin, but they do speak size, shape and color. You just have to feed them!

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