Fly Fishing with Terrestrials in Colorado

August in Colorado and throughout the West means it is time for dry fly anglers to focus on fly fishing with terrestrials. The big July aquatic insect hatches of caddis, stoneflies and mayflies have waned and land-based insects are now being eaten in large numbers by hungry trout. During late summer and early fall, trout become less selective when eating on the surface and will devour a wide-range of terrestrials, from tiny black ants and giant yellow grasshoppers to clumsy beetles and even spiders, wasps and little jassids.

This is the case from the highest alpine lakes above tree-line down to low elevation large rivers. Just when the predictable hatches taper off, nature provides trout with a huge biomass of terrestrials that commonly end up in the water, where they are general pretty easy to capture and consume.

Not many anglers appreciate a windy afternoon in August, but these conditions often provide the best terrestrial fly fishing scenario in Colorado’s rivers and lakes during late summer. The breeze dislodges ants, hoppers and other critters from nearby bushes, grass and trees where they end up floating helplessly in the water. This isn’t to say that fly fishing with terrestrial patterns will not produce fish in the mornings or evenings since the trout become accustomed to seeing all manner of these insects throughout the day.

Here is a quick look at the most important terrestrial insects and fly patterns for fly fishing in Colorado.


Grasshopper Fly

This is a great summer combo for Colorado anglers.

Everyone loves hopper fishing. They are big and trout eat them with gusto. During most years, August and September see the peak of the hopper hatch. Color schemes vary widely from bright green, to tan to pale yellow. Sizes can also range greatly from tiny size 14 baby hoppers to giant size 2 behemoths nearly three inches long. Catching fish on hoppers is all about finding the right holding water next to a grassy or brushy bank. Some anglers prefer gaudy foam patterns with crazy rubber legs like the Chubby Chernobyl while other like a lower riding more natural pattern such as Schroeder’s Parachute Hopper. Let the trout be your guide.


Carpenter Ant
Trout love ants and they are good trailer fly behind a big hopper.

Chernobyl Ant Original

Ants are everywhere and trout know it. This time of year when you see a single random sipping rise, chances good that trout just ate an ant. Carry black and red patterns from size #18 to #12. I like foam black ants that imitate the larger carpenter ants well. More traditional dubbed body ants can often be very effective fished sunk since ants often end up washed under the surface.


Fat Albert
Don’t overlook the abundance and importance of beetles.

Fat Albert

Fly fishermen in Colorado tend to overlook beetles for some reason. I’m guilty myself and tend to mostly fish them on lakes. But the fact of the matter is that beetles are the single largest group of insects found in the world. They exist nearly everywhere except the extremely cold regions found near the poles. Billions of beetles of hundreds of different species line the banks of every trout stream or lake in the world. Sizes vary widely but color schemes tend to be dark and shiny. Keep this in mind when choosing your fly pattern.  It’s hard to beat a small black Fat Albert  on the Colorado River.

For more information on the best terrestrial fly patterns, the latest fishing conditions or to book a guided fly fishing trip, check out the Vail Valley Anglers fly shop in Edwards, Colorado and chat wit our expert staff.
Brody Henderson, Guide and Content Writer