As May progresses toward June in Maine’s bottom third, rivers and streams start producing predictable aquatic insect hatches that send trout and salmon into feeding binges on most days. These emergences create pleasant memories to help get us through severe winters.

Fly-fishing friends often talk about common mayflies and throw around Latin names such as Paraleptophlebia adoptiva, Ephemerella subvaria and Drunella cornuta. This has nothing to with snobbery but rather pragmatism.

If a friend plans to accompany me to a river I can say, “There will be a Stenonema vicarium hatch,” and he or she will bring that fly pattern in the correct size, silhouette and color scheme to match the exact bug.

My reason for this spiel about Latin names has a more relevant point. Most fly-fishers I know may refer to mayflies in a foreign language but when it comes to caddis flies that are equally as common in Maine, we often switch gears and say, “The caddis with a medium-olive body and light-dun wings is hatching on the upper Medomak River right now.”

Yes, this generic description for caddis discussions is slowly changing to Latin names, particularly for the younger generation when they discuss the ubiquitous Trichoptera order. God bless their diligence, but I’m slower to change, even though I studied Latin in school.

This fly-fishing quirk of using 1. Latin for mayflies; and 2. colloquial words for caddises has long fascinated me, and knowing why the sport evolved this way helps fly rodders because the answer relies on understanding aquatic-insect behavior in trout streams.

For starters, most emerging mayflies swim up from bottom and perch on the surface film to dry their newly forming wings before flying ashore to transform into egg-laying spinners. A kid can observe this behavior and make the connection – floating flies attract foraging trout that sip them.

Serious fly fishers learn to catch the targeted mayfly and match it to a natural in size, color scheme and silhouette. They then cast upstream of a rising trout and dead-drift the fly over the lie. For consistent success, the fly must float at the current’s exact speed to duplicate that behavior.

Once mayflies and caddises fly ashore, they hide under foliage or perch on bark to escape detection. These insects have evolved with certain body and wing colors to match bark or underside of leaves. Insects in early season before foliage dominates are often dark to match bark, and bugs in summer are light green or cream to match the backside of foliage.

Some mayflies like Isonychia bicolor, a summer hatch, are an exception.

This species swims to shallows near shore and crawls onto say, dry rock tops or onto bridge abutments, to dry their wings where trout cannot eat them. So fly rodders must match them in their larva stage. On the other hand, most mayflies drying their wings on the meniscus hope fish won’t gobble them during their long float.

Caddis are devils to match. Many emerge by swimming furiously from the bottom, bursting through the surface film with a barely perceptible dimple and then flying ashore. When fish concentrate on hatching caddis, they make showy surface splashes because the fish are chasing the fast-swimming bugs to catch them before they escape into the air.

We get little chance to scoop a fast-escaping caddis off the water with a baitfish net or even have an opportunity to see one flying – unless we’re standing exactly beside the spot where one breaks from the surface film.

The secret to caddis hatches begins with matching an imitation fly to the body and wing color, and the body proves the most important consideration. Once we ascertain body color of the emerging caddis, we’re usually in business to catch fish.

During a hatch I like to cast a dry-fly imitation such as an Elk Hair Caddis downstream and quartering across the current. I want the fly wet enough to sink and swing in an arc across the flow, and then I retrieve it in 4- to 6-inch strips, trying to get the right speed to attract a strike.

At this time a stripped fly imitates a caddis swimming from bottom, and it works far better than a dead-drifted, surface fly.

Many folks accustomed to dead-drifting mayflies stick to this presentation with caddis and watch experienced caddis casters nearby having all the fun.

Caddis are a tough hatch to crack and this tactic above is just one of many – a common one that leads to success – and it often works during these prevalent hatches on Maine rivers and streams.

Ken Allen of Belgrade Lakes, a writer, editor and photographer, may be reached at: 

[email protected]