The health of our rivers is directly related to the health of our snowpack. This winter’s snowpack was not only fantastic for the ski resorts, but it was equally fantastic for our rivers and streams. As we head into the last push of the runoff from a really great winter the anticipation of the first summer hatches of bugs start to make every fly angler get excited. On most western rivers that hatch is the Caddis fly. This hatch is one of the most anticipated aquatic insect emergences of the year on the Eagle, Colorado, Roaring Fork rivers as well as most larger freestone rivers and tributaries throughout Colorado. While there are over 14,000 different species of caddisflies worldwide here in the the Rocky Mountain west, we are only interested in a few select species of this prolific aquatic insect.
Life Cycle: Caddis flies undergo complete metamorphosis, which means they go through four distinct life stages: egg, larva (nymph), pupa, and adult. The larvae, known as caddisfly nymphs, spend most of their lives in the water and construct protective cases made of silk and various natural materials like sand, pebbles, or plant fragments. These cases serve to protect the larvae from predators and provide them with camouflage.
An important factor in their importance to Fly fishers is that they go through a complete metamorphosis.
Brachycentrus americanus: Commonly known as the American Grannom. This is probably the most prolific Caddis species on our river systems. The best way to describe this Caddis fly is that it’s the Cased Caddis. The Cased Caddis builds its cocoon like case from the wood it attaches itself to under the water surface. That’s why they are almost exclusively found on sticks and branches.
Hydropsyche: Another Caddis species very common to the rivers in Colorado. These caddisflies are known as net-spinning caddisflies due to their larval behavior of constructing silk nets to catch food particles in flowing water.
Rhyacophila: This is known as the free-swimming(living) Green Caddis and lives in faster more oxygenated water.
When it comes to fishing a caddis hatch there’s some good things to know before you jump in the water. Caddis fly hatches on rivers can occur under a variety of conditions, but there are a few factors that are generally considered optimal for a robust hatch. Here are some key elements that contribute to a favorable environment for a caddis fly hatch on a river:
Water Temperature: Caddis flies prefer water temperatures between 50°F (10°C) and 60°F (15.5°C). This temperature range is commonly associated with spring and early summer seasons when the water is cool but not too cold.
Water Quality: Caddis fly larvae, also known as caddisfly nymphs, are sensitive to water pollution. Clean, well-oxygenated water with low levels of pollutants and contaminants is preferred for their healthy development.
Flow and Current: Moderate water flow with a gentle current is generally favorable for caddis flies. The nymphs, which spend most of their lives underwater, need enough current to deliver oxygen and food but not so much that it becomes difficult for them to anchor themselves to the river substrate.
Photoperiod and Light Conditions: Caddis fly hatches are often triggered by specific light conditions and photoperiod cues. Generally, they tend to hatch during the late morning or early evening when light levels are lower. While a decrease in ambient light, such as during dusk, can stimulate the emergence of caddis flies. Over my 28 years guiding we have observed that caddis also hatch as the sun begins to hit the water in the mid mornings. The nice thing is that you don’t have to be on the water at 6:00am.
It’s important to note that specific caddis fly species may have unique preferences and adaptations, so optimal conditions can vary depending on the species in question. Additionally, regional and seasonal variations can also influence when and where caddis fly hatches occur. That’s why a quick call to your local fly shop before hitting the water can be a great benefit.