Entomology Primer

Understanding fly fishing entomology, or the aquatic environment and the insect life that thrives there is important facet of the fly fishers’ skill set.

The different stages of an insect’s life cycle determine what trout will be feeding on, and answers the other w’s of when, where, and why. Identifying the insects and which ones the fish are keying on, then “matching the hatch” is often critical to success.

A hatch refers to the time of year, and time of day that an insect emerges from its nymph or pupal stage (spent mostly in the water), crawls out of the water, or floats to the surface, dries, sheds its exoskeleton and emerges into its adult, winged, terrestrial form.

The food chain begins with microscopic organisms such as algae, flagella, diatoms, bacteria, and protozoa otherwise known collectively as plankton. These are food sources for larva and pupal form of aquatic insects such as Chironomid and Chaoborus (midges and mosquitoes) that in turn are fed on by larger orders of insects, such as, mayfly and stonefly nymphs, damselfly and dragonfly nymphs as well as shrimp, leeches, water boatman etc. At the various stages of their life, trout will feed on all these creatures. Trout fry feed on plankton and chironomids and, as they grow, their diet changes.

Of course, the presence and diversity of insects depends upon the aquatic environment as well as the time of year and time of day, so vary your fly fishing and flies selection and come prepared.

Chironomid emergence from larva (bloodworm) to pupa begins in early spring when the water warms to about 5 C. Still too cool for other insect hatches, the trout feed heavily on these pupa and larva during this period.

Other insect hatches occur later. As the water warms and the season progresses stoneflies, mayflies, caddisfly, dragonfly, damselflies as well as terrestrials such as grasshoppers, flying black ants, cicadas and beetles become active and are all food sources for cruising trout.

The observant angler is a successful one – be sure to observe your surroundings, match the hatch.

Local Hatches

Caddisfly

From June to August the caddisfly hatch on the Columbia River near Trail and Castlegar is one of the natural wonders of the world.

Millions of the Grannom and spotted caddis emerge from the river and form like thunder clouds above the surface. While the heavy hatch may be a minor annoyance to anglers, the caddisflies are a consistent and plentiful food source for feeding trout all summer long.

The caddis belongs to Family Phryganeidae, of which there are over 20 species of caddis in North America. Caddisflies have a full life-cycle, from egg to larva, pupa, and adult to repeat the process. They emerge from eggs as larva on the bottom of rivers and lakes, form tubes made of pebbles and other bottom debris to build cases as they pull themselves along the bottom and feed on algae and other detritus.

After about two years and five instars the caddis pupa emerges and begins its swim to the surface, propelling itself with powerful back legs about four to six inches at a time. The journey is rife with dangers as trout and other water mammals feed voraciously on the emerging caddis. However, it is a perfect time for fly anglers to target trout by fishing emerger patterns.

Upon breeching the surface, the adult breaks through the pupal shuck with its wings upright to dry briefly, then fold tent-like over the caddis’ body. It will skate across the surface, then take flight to mate over streamside vegetation before returning to the water to deposit eggs.

When not in flight, the adult caddis holds its long, tapered wings tent-like over its body, with lengthy antennae protruding forward. The caddis is an erratic flyer that emerges in the late afternoon and early evening.

Techniques: As a fly fisher, it seems overwhelming to have to compete with hundreds-of-thousands of naturals trying to draw a trout to your imitation. Even with all this competition big rainbows still manage to take a favourite caddis pattern as it floats amidst a crowd of emerging adults.

The dry fly action on the Columbia can be frantic. The action begins early in the afternoon with fly fishers nymphing caddis emerger patterns. When the sun sets and darkness falls be prepared for the real wild rainbow feeding frenzy to begin. Use a dry fly imitation that rides on the surface but slips under on the retrieve imitating an emerging caddis.

Fly Patterns: There are numerous caddis dry-fly patterns including the popular Elk or Deer hair caddis, parachute caddis, Goddard, or Tom Thumb. Emerger patterns include the Sparkle Pupa, Pulsating Caddis, Iris Caddis and Klinkhammer Caddis can be fished naked on floating lines or with indicators, as well as on sink tips early in the day.

Mayfly

Mayflies are another delicacy for rainbows that come in a variety of shapes and sizes. Blue-winged olives and pale morning duns emerge early in spring, and in summer Green Drake and hexagenia hatches are highlights, mixed in among the clouds of caddis.

Trout will key on mayfly hatches, despite the robust caddis hatches, as they stay on the water longer and are likely a welcome change of diet to the steady stream of caddis. Mayflies thrive in clear, clean, and fast water so hatches are often more pronounced at the mouth of tributaries like Beaver and Bear Creeks.

On rivers like the Columbia and its tributaries, the mayfly nymph will crawl out of the water and dry on shore, shedding its exoskeleton, and emerge as the dun or sub imago. Upon emergence the mayfly “dun”, once its wings dry, will fly to nearby bushes or weeds where it will shed its outer skin once more and become the mayfly “spinner” (imago).

This is the reproductive stage of their life cycle. During this stage, mayfly males will swarm and fly in a bobbing motion over the water. The female flies straight through these swarms allowing a male to clasp onto her and engage in a lethal consummation.  Once the two mate, the male goes off and dies while the female releases her eggs by dipping her abdomen onto the water’s surface. Once complete, she’ll then also fly off and expire without ceremony in a process called semelparity.

Technique: Depending on the species of mayfly hatch and type of water, the approach and technique will vary.

Adult mayfly patterns are best fished with a fly rod, but many anglers on the Columbia use a spin caster and bobber with a dry fly, and have great success floating them in eddies and deep pools.

When the hatch is on, usually during the late morning and early evenings, large trout will often abandon all caution and feed aggressively on these flies as they touch down on the surface depositing eggs or expiring.

For fly anglers, when nymphing either use a type-6 sinking line with relatively short leader (4-6 feet) or a floating line with strike indicator and a weighted nymph. Adjust length of leader and tippet according to depth.

On rivers and streams cast into the current and allow the nymph to tumble along the bottom. When it reaches the end of its drift, retrieve it slowly to imitate it crawling along the bottom. Often on the swing is when you will get most of your strikes so be ready.
If casting dry flies on the softer water, presentation is very important. Light tippets and good imitations generally mean better success.

On riffles, runs and tailouts cast at a 45-degree angle up stream and allow the fly to free-float downstream. Stack line as you get to the end of the run to prolong the drift.

Fly Patterns: For mayfly imitations use sizes 12-16, depending on species: Adams, Blue Dun, PMDs, March Brown, Grizzly Wulff and the humpy. Mayfly nymphs are also effective patterns to fish sub-surface. Some of the more popular nymphs are the Prince, Pheasant Tail, Hare’s Ear, and Hendrickson nymphs.

Stonefly

Stoneflies are an important food source for rainbow trout throughout the year.

Depending on geography and weather, the spring salmonfly hatch can be one of the most exciting times of the year for fly fishers.

The largest of aquatic insects require clean, cold-water habitat and live among the rocks of fast-flowing riffles and runs. April brings the first emergence of the golden and salmonfly adults, so imitating stonefly nymphs leading up to the hatch is a favoured tactic for catching big trout on the Columbia.

The golden stonefly species, Caleuneria californica, of the Perlidae family, and the giant western stonefly, Pteronarcys californica, also known as the salmonfly, are common and at times abundant on many western streams.

Pteronarcys engage in behavioural drift. In the morning first-year nymphs will emerge from underlying rocks and vegetation to feed. Second year nymphs will then follow, grazing for a while, before making way for the mature third-year nymphs.

While grazing, nymphs often lose their tenuous hold on the substrate and tumble downstream into the waiting mouths of large trout. When they prepare to emerge into the adult form, their activity increases, and they move into shallow water, closely followed by rainbow trout.

The adult Pteronarchys californica has a bright orange body with dark abdomen, two large antennae and two pairs of cross-hatched wings that lie flush against its body at rest. However, when forced to the water, its wings often move erratically splayed, its body riding low on the surface. The adult salmonfly commonly grows to almost three inches in length, so casting large dry-fly imitations is highly recommended

Technique: Early in the season, nymphing stones is your best bet for success. Use a strike indicator with six-to-10 feet of leader, tie on a micro-swivel with about 12-inches of tippet to help get the nymph-pattern down or weight the nymph itself with wire or beadhead.

These weighted flies can be drifted through the seams of large eddies, riffles, runs and tailouts, and when the indicator goes under, set the hook, and hang on.

Using sink-tip and sinking line is also effective. Cast about 45-degrees up river and let line move through run or riffle. Just before you begin the retrieve, the action of the line stopping raises the fly, and as it moves abruptly up and away from an interested trout, the shift in direction (the swing) triggers a response that often results in an aggressive take

When casting dry flies, the adult salmonfly pattern is not your usual delicate presentation but rather a deliberate and aggressive touch-down on the water`s surface. Gravid salmonflies dip their abdomens onto the water and release their eggs, but because of their size and erratic flight pattern, gusting winds will often knock them off course and force a hard landing creating a substantial splash down.

A fly angler tossing adult patterns should occasionally try to imitate the same hard landing when throwing line. Aim your delivery low so that it lands with a not-so-subtle splash or use a sidearm cast where the fly descends with conviction, alerting cruising trout. Allow the pattern to drift drag-free, then twitch and skate it across the water, let it drift some more, repeat, and get ready.

Flies: Popular stonefly-nymph patterns include the Evolution Stonefly, Kaufmann’s Stonefly pattern, Giant beadhead stone, or JB’s.Stoner.

Adult stones can be imitated with stimulator patterns, with size 10-12 yellow bodies for golden stones, and size 6-8 orange bodies for Salmonflies. Other patterns include the Clark’s Fork, Foam Fork, Sofa Pillow, Phil’s salmonfly, and the Columbia River salmonfly pattern.

Chironomids

Chironomids: Like stillwater fly fishing, chironomid fishing on the Columbia River is an effective technique for targeting rainbow trout.

Chironomids or midges are the first insects to emerge in early spring, starting as soon as the water temperature warms to about 5 C. The Columbia hatch can start as early as March and continue through to November.

Mosquitoes and midges begin their life in larval form ( ie: bloodworm stage)and stay that way for up to two years feeding on diatomes before emerging into the pupal stage.

The pupae gather gasses under their abdomen, ascend and become shinier as they rise to the surface. Once the chironomid reaches the surface, a split forms in their thorax and the adult emerges fully formed and flies off.

Fly anglers mainly target Chironomidae and chaoborus (midges and mosquitoes) in the pupal or larval form.

But unlike stillwater angling, chironomid fishing on the Columbia has its own unique challenges.

Finding the sweet-spot for depth can mean the difference between a good day and a great day. A fish-finder is a helpful device on the Columbia in identifying what depth most trout are feeding, but the currents, deep pools, and sweeping eddies can play havoc with your line.

Trout usually cruise at a depth of about six- to 12-feet, feeding on the abundant supply of chironomid pupae as they rise to the surface.

Technique: Fly anglers use a strike indicator on a 12-foot leader. Tie a micro-swivel to the leader and attach about 12-24 inches of tippet. Tie on a size 12-16 chironomid pattern with a loop knot to help impart a livelier presentation.

Keep a close eye on the indicator and slowly retrieve the fly. Casting against the wind is recommended as trout feed against the prevailing current.

Fishing from shore is also possible for fly anglers and gear fishermen. A spin caster with a weighted float and chironomid pattern can use a similar technique casting off the rocks near Rock Island or wading into a riffle and cast into the seams, letting the current carry the rig into the eddy or run.

Similarly, the technique works well for fly-fishers casting their strike indicator-chironomid setup through runs, deep pools, and back eddies. Keep a close eye on the indicator or float and adjust the depth or chironomid size and colour as required.

Using these still-water techniques in the Columbia River will keep your lines tight with non-stop action.

Fly Patterns: blood worm, hylos, chromie, anti-static bag, copper-top, EC chironomid, gas bead.

Terrestrials

Flying Black Ant

The flying black ant hatch emerges with the first sign of summer heat. A two-day hot spell will induce the terrestrials to hatch, but it can be as fleeting as it is abundant, if rain and cool weather follows, the hatch can shut down as fast as it started.

Black ants fly well over land and are often attracted to water, yet, as soon as they get over the Columbia River the temperature drops a few degrees and this puts a damper on their flight pattern, as they’ll often drop to the surface and become prime fish food.

The flying-ant emergence heralds the turning point of spring to summer fishing, when fish start to think that food can be found on or near the surface instead of always on the bottom. Afternoon until dark will find trout looking for food near the surface on any hot summer day.
Fish a flying ant pattern with a floating line, and nine to 12-foot leader to keep the fly floating naturally and with little drag.

Cicadas

On the Upper Columbia, the cicadae emerge in May, and will gather on the concrete walls or other structure to let their exoskeletons dry and pump blood into their wings before they fly off to mate.

The adult cicada will also feed on streamside deciduous flora, such as poplar, willow, and cottonwood, and lay their eggs in the branches. Once the eggs have hatched, the larva fall from the tree and burrow into the ground feeding on rootlets from two to 17 years, depending on the species, before emerging.

Like the flying ant, their flight over water often grounds them and their desperate struggle on the surface attracts trout. Skating the imitation in big eddies will result in more strikes, or letting it drift along on a riffle or run will have large rainbows throwing caution to the wind and engulfing these large morsels.

The hatch can last anywhere from a few days up to a month, depending on the weather.

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