The Absolute Beginner
A Fly Fisher's Basic Entomology, Part One
We've had a number of enquiries from novice fly fishers about
the entomology of fly tying. This is understandable, as the
complexity of species and the various metamorphoses they
manifest can be confusing. A one-page column is no place
deal with such complexity, but beneath the complexity there
lies a relatively simple basic pattern which is easy to explain
and understand. Moreover, once it's understood, it provides
two clear conceptual frameworks on which to hang the
profusion of details which come later.
The two frameworks are:
- 1. The kinds of flies. These are what biologists call "orders."
There are many of these, but only a few are of interest to the fly
fisher. In fact, the vast majority of artificials are tied to imitate just
three orders: mayflies, caddis flies, and stoneflies. There are others,
such as midges, which are also important, but tend to be more
restricted in terms of habitat and geography. All are winged insects
which are hatched and spend their larval stages under water.
- 2. The stages of development. These are the larva (or nymph),
the pupa (or chrysalis), and the winged adult. There are differences in
how the three orders go through these stages, but they're easy to
By far the majority of artificial fly patterns are mayfly imitations.
With a few exceptions these correspond to the three stages and
one transitional stage of development.
Mayflies lay their eggs on the water and the nymphs (larvae) develop
on the bottom. Most spend a year there before hatching, although a
few of the larger species spend two. Nymphs are generally split into
four categories: swimmers, which dart about on the bottom in the
faster water; clingers, which cling to rocks (usually the underside)
in fast water; crawlers, which crawl around in the stuff on the
bottom; and burrowers, which burrow in soft sandy or muddy
bottoms in slower or still water.
All have distinctly different body shapes suited to their habits
and habitat. Swimmers are slim and streamlined; clingers are
flattened with strong, thick legs; crawlers are plump and
cylindrical with thinner legs; burrowers are long and slim
with feathery gills.
Artificial flies tied to imitate nymphs conform to these body
shapes, and are designed to be fished on a dead drift beneath
the surface, usually close to the bottom.
Mayflies do not have a pupal stage. The dun (adult) hatches directly
from the nymph. In some species, the nymphs simply swim to the
surface and split open, allowing the dun to crawl out. Because this
happens while the creature is floating down the stream, they're prime
targets for feeding fish. Many of the legendary mayfly hatches are of
this kind, such as Hendicksons and Blue Winged Olives.
Other species crawl out of the water on to rocks or emergent
vegetation and hatch there. Some fly away without touching the
water, but many get caught on the water and drift downstream.
Imitating these downstream drifting flies with an artificial is the
essence of classic dry fly fishing. This is where "matching-the-hatch"
started. Artificial flies tied to imitate duns are designed to float either
right on the surface or just in the surface film. Most have stiff hackles
to aid in floating.
As they float downstream, the newly hatched duns dry their wings
in preparation for their first flight. The time this takes varies according
to the dryness of the air, the heat of the sun, and the degree of wind - just
like the wash hanging out on a clothesline. Those which are fortunate
enough not to be eaten by a fish, take to air and head for the vegetation
along the banks of the stream. Here they have to run another gauntlet - birds
this time. One of the indicators that a hatch is going on, even though
the flies might not be immediately visible, is the activity of swallows,
waxwings, kingbirds and other fly-eaters working above the stream.
In the face of so many predators, it's a wonder that any flies
manage to make it to the safety of the streamside foliage, but
thousands do. Here, they rest for the day\emdash sometimes two.
And, as they rest, they go through a final metamorphosis: the skin
splits, and a very different fly emerges. Unlike the sombre coloured
dun, this second stage adult has a hard, almost metallic sheen to its
body, and its wings (in most cases) rather than grey or brown,
are crystal clear.
This stage of the mayfly is called a "spinner." The name is very
old, and derives from the behaviour of the fly over the water. Once
the metamorphosis is complete, the spinners return to the air above
the stream, where clouds of them dance or "spin" together. This is
their mating ritual. Gradually they will drop closer to the water, and
you'll see males and females coupling in the air. When this is done
both males and females drop to the water, dying. This what we call
a "spinner fall." Again, the fish are provided with a feast, but enough
fertilized eggs from dying females sink to the streambed to ensure
survival of the next generation.
Spinner imitations, like duns, are designed to float, but unlike duns,
which have upright wings, they have horizontal wings, which lie flat
on the water. Like duns, they are usually fished dead drift with either
an upstream or an across stream cast.
In our next issue, we'll publish the second part of this basic entomology - just
in time for the opening of the resident trout season. This will cover
the other orders of flies, as well as some variations on the basic
mayfly patterns, such as emergers, crippled duns, and drowned spinners.
If you just can't wait until the next issue of the Canadian Fly Fisher,
you will find more on the specific insects in the
Not Quite Entomology section - or Fly Fishing