The Beginner’s Guide to Life Cycles of Flies
A lot of fly fishing is based on imitating the insects that trout feed on. Understanding the basics of insect life cycle can help you hone in on what trout are feeding on, which in turn can help you catch more fish.
There are textbooks and encyclopedias written on life cycles of every species of insect that lives in the water, numbing the mind with entomological terms and fancy sounding Latin names. This will break it down to the essentials to prime your knowledge of bugs and knowing the food source is key to knowing how to catch fish.
Key Points
Each species of fly has its own unique life cycle with different names and timespans, but essentially it boils down to 4 main stages: Egg, Nymph/Larvae, Emerger, Adult. Each fly starts as an egg and grows into a nymph where it spends most its life. Those nymphs then emerge into egg-laying adults.
Species of Flies
There are 4 major groups of flies that trout feed on, depending on your specific location and ecosystem:
Each of these groups of flies may be present in your water system, though one may be more prevalent depending on location and the time of the year.
Mayflies
Egg–>Nymph–>Emerger–>Dun–>Spinner
Mayflies are very common in trout streams and can be identified by clear, upright wings.
Almost exactly 1 year after they hatch from their eggs and grow into nymphs, mayflies are ready to fly.
When they are ready to hatch into flies, they swim/drift up to the surface of the water column and begin to split from their exoskeletons. These is the stage known as emerging.
Once they have shed their shells, they float on the surface to dry their wings and prepare for flight. This stage the fly is known as a dun.
Once they are able to fly (and aren’t eaten by a hungry fish), mayfly duns will fly to trees/brush and molt (shed) into what are known as spinners. The spinners will mate soon after.
The spinners mate, lay eggs, and quickly pass away. Then the cycle begins again.
Caddisflies
Egg–>Larvae–>Pupa–>Emerger–>Adult
Caddisflies are another big source of food for trout. They can be identified by condensed wings that are parallel to the body at rest.
Majority of caddis larvae build cases out of natural debris in the water. They protect the larvae from predation and help anchor them to the stream. They spend about a year in this larvae stage.
Caddisflies have another stage known as the pupa stage. This is when they shed their cases and begin to float to the surface.
After floating to the surface, they emerge into winged adults. Adult caddisflies live up to a month before laying eggs and dying.
Stoneflies
Egg–>Nymph–>Emerger–>Adult
Stoneflies live as nymphs underwater for 2 to 4 years.
Unlike mayflies/caddisflies, nymphs often swim to shore during emerger stage, which makes it tough for anglers to imitate.
After emerging to adults, stoneflies are notably clumsy fliers and often get blown into the water.
Similar to other flies, adult stoneflies return to the water to lay their eggs
Midges
Egg–>Larvae–>Pupa–>Emerger–>Adult
Midges are another plentiful food source for trout. They’re often smaller but swim in huge swarms.
In the larvae stage, midges have a distinct worm-like appearance.
Pupae form from larvae. From there, pupa emerge into adults very quickly (a matter of seconds) when they are extremely vulnerable to trout.
Adults emerge at the surface, often in huge swarms that trout feed upon.
Summary
Understanding fly life cycles can be as complicated as you want it to be. Knowing the basics can help you understand what and how trout feed, which in turn will help you catch more fish.
