Our Man In Canada
May 18, 1998
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Mayfly Primer
These insects are the foundation of fly fishing
by Clive Schaupmeyer



Adapted from The Essential Guide to Fly-Fishing by the author. With apologies to entomologists and ultra keen fly anglers this is a brief introduction to the bugs we most revere.

May Fly Hooks

Mayflies are the foundation of fly-fishing. The purest of "pure" fly anglers argue that you are not fly fishing unless you are casting a dry fly upstream to rising trout during a mayfly hatch. Fine. But most of us just appreciate them for what they are-beautiful bugs that trout eat and we can imitate with wet and dry flies.

They have neat names like Pale Morning Dun, Hendrickson, Light Cahill and Blue- winged Olive.

Mayflies are one of the most obvious groups of insects in trout streams and are of immense interest to fly anglers. They occur in large numbers and are a favored food of trout and other fish. The aquatic forms (nymphs) and adults (duns and spinners) lend themselves well to imitation with artificial flies. Fishing a good mayfly hatch can be pure delight-or hard to figure out.

Mayflies belong to the order Ephemeroptera ephemero, meaning "short lived" and ptera meaning "wings." Adults are slender, winged insects with two or three long, thin tails. Different species range in length from under 1/4 inch to well over 1 inch (4 mm to about 30 mm). Most species have four wings; however, only one pair is large and obvious. Wings of the first stage (dun) tend to be dull or darkly mottled. After the adult mayflies have molted into the second land stage (spinner), the wings are light and translucent. Spinner wings may be mottled.

Body colors range from pale to black with shades and mixtures of tan, grey, cream, green and brown predominating. Bodies are often banded with shades of colors because they are segmented. Mayfly bodies are often lighter on the bottom than top, which can be important when selecting the right fly.

Mayflies undergo incomplete metamorphosis, which means they miss one of the underwater stages common to some other insects. This cycle starts with an adult female laying eggs in water. The eggs fall to the stream or lake bottom and soon hatch into nymphs. Depending on the species, mayfly nymphs crawl around the bottom, cling to rocks, swim freely or burrow into silt. Most species spend one year in the water, and all but the burrowing nymphs are eaten by trout regularly. The nymphs are imitated with wet flies we call nymphs.

Exactly one year (give or take) after the eggs are dropped into the water, the nymphs swim to the surface and emerge, or hatch, as we say. This is of great importance to trout and trout anglers. The nymphs that have spent the last year crawling around and under rocks now have to swim to the water's surface. During this brief trip they are vulnerable and trout feed readily on them. At the surface, adults emerge from their skins or shucks - more correctly known as exoskeletons - and pump fluid into their wings. They sit on the water surface like little sailboats for anything from a few seconds to a few minutes while their wings dry. They can emerge, or hatch, like this by the thousands and trout love them. We use dry flies to imitate them while they are riding down the river drying their wings.

Drawing of mayfly

The adults, called duns because they are usually dull colored, then fly to nearby bushes. After a few hours-or perhaps a day or so-the duns molt into a second land stage and are now called spinners. The spinners mate near or over water, and after a short incubation period the females return to the water surface and drop their eggs, thus completing the cycle. The females usually die on the water surface with wings splayed apart. We call them spent spinners.

Most mayflies have one life cycle per year. However, some mayflies, like the many species of the blue-winged olives, are reported to have two or more life cycles per year. Blue- winged olives hatch in the spring and again in the fall if conditions are right.

Popular dry flies that imitate mayflies include the generic but widely effective Adams in standard and parachute styles; light-colored patterns, like Light Cahill, Light Hendrickson or Pale Morning Dun; Blue-winged Olive; and patterns like Dark Hendrickson, Quill Gordon or Rusty Spinner. Other mayfly dries of regional importance include forms of Green and Brown Drakes. Typical hook sizes for many mayfly species range from #12 to #18; however, a few are much larger and some smaller. Popular mayfly patterns vary from east to west as the species change.

Popular nymphs that imitate the underwater stage of mayflies include Hare's Ear, Pheasant Tail; Zug Bug; Prince Nymph; and Blue-winged Olive Nymph. There are subtle differences in body thickness (or at least length-to-width ratios) between various types of mayfly nymphs. But the general shape and pattern of the popular Hare's Ear resembles most mayflies' distinctive carrot shape. Most mayfly nymphs can be successfully imitated with a generic patterns (like Hare's Ears) tied in different body colors and a few sizes.

Emerger patterns imitate mayflies as they break through the surface film and out of their nymphal shuck. They are usually a hybrid of nymphs and dry flies. Typically emerger patterns are a nymph with a ball of floating material like poly yarn or foam tied near the head. The idea is to simulate a nymph floating at the surface and starting to crawl out of the nymphal case.

For further reading about mayflies and insects, find copies of the following

        'Handbook of Hatches' - by Dave Hughes
        'Mayflies' - by Malcolm Knopp and Robert Cormier


Our closing thought is attributed to
Mark Twain
" Golf is a good walk spoiled "

Bio on Our Man In Canada
Clive Schaupmeyer is an outdoor writer and photographer. He is the author of The Essential Guide to Fly-Fishing, a 288-page book for novice and intermediate fly anglers. His photo of a boy fishing was judged the best outdoor picture of 1996 published by a member of the Outdoor Writers of Canada. He fly-fishes for trout in Alberta's foothill and mountain streams and for pike near his home in Brooks, Alberta. For information on where to find, or how to get a copy of Clive's book, Click here!
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