.......................  ......Fly Fishing Yellowstone National Park


Bug Made Easy

At the request of several people in various ways regarding basic questions
about aquatic insects, I though I would run this article I wrote a year or two ago.

Identifying Bugs:
Probably most of you can tell one type of bug from another but for those who
can’t, or are just getting started fly fishing, let me briefly cover some basics of

An aquatic insect is one that is born and lives most of its life in the water. A
terrestrial insect is one that is born on land and spends all of
its life on land, unless it accidentally falls or is blown into the water.

Mayflies, caddisflies, stoneflies and midges are aquatic insects. Grasshoppers,
ants, crickets and such are terrestrial insects. There are others that fit into
these categories, damselflies, dragonflies, crane flies, and so forth, but for the
most part, this represents the bugs trout eat. Trout Bugs 101 is being able to tell
a caddisfly from a mayfly from a stonefly from a midge.

Mayfly Nymphs:
Mayfly nymphs have either two or three tails. They can be easily confused with
stonefly nymphs. If you are not sure, check their legs. Mayfly legs end with a
single claw and stonefly nymphs with two claws. Plate like gills are present along
the abdomen of a mayfly.

Stonefly Nymphs:
Stonefly nymphs have two short tails.  Their legs end with two claws. They either
have no visible gills or their gills are found under their head or upper body.

Caddisfly Larvae:
A Caddisfly larva looks like a little worm or if it is a cased caddis, a little worm in
a case with its head and maybe its tail stuck out. They are very easy to
distinguish from a mayfly or stonefly nymph.

Midge Larvae:
A Midge larva is a tiny, worm looking creature that is usually burrowed in the soft
bottom of the stream or lake. They can be confused with an uncased caddisfly
larva, but for the most part, are much smaller. Now lets look at the adult flies.

Adult Mayflies:
Mayfly adults look like little sailboats on the water. The have two, larger upright
wings and can and usually do have two little ones called hind wings.  

Adult Stoneflies:
Adult stoneflies have (4) four wings but they are folded flat on top of the fly and
look like one wing when they are at rest. In the air, they look larger than they
really are.

Adult Caddisflies:
Adult caddisflies also have (4) four wings but they are folded in a tent shape
when the fly is at rest. They two look much larger in the air than they really are.

Adult Midges:
Midges are tiny (2) two winged flies that look like mosquitoes. Much of the time
they are difficult to see in the air or on the water. Don’t just assume the small
flies you see are midges. They may be mayflies. Take a closer look.

You should learn to be able to recognize these (4) four different types of flies as
a nymph or larva, as a pupa (if this stage of life exist), and as a full grown adult
whether they are at rest, on the water or in the air. There are others, but they
are easy to tell apart, like the crane fly, the dragonfly and the damselfly.  

Mayflies 101:
Most of you probably familiar with the life of a mayfly, but for those who don’t,
here is a brief overview. I’ll call this Mayflies 101. The mayfly life cycle is one of
incomplete metamorphous - a big word that means he or she starts their life as
an egg and then as a nymph that has several stages of growth or instars they
are called. In other words they get larger and larger during the one to two years
(usually one) that they are nymphs.

When they hatch, they turn into adult flies, which anglers call duns. In short, the
life cycle of a mayfly is an egg, a nymph and a dun. During its entire life, which
is usually a year but can be two years depending on the species, the mayfly is a
fly with wings only for a day or two, sometimes even less. Caddisflies and
Midges undergo complete metamorphoses which means they insect start as an
egg, then become a larva, then a pupa and finally an adult.

Types of Mayfly Nymphs:
There are basically 4 types of mayfly nymphs. The swimming nymphs that
actually can swim, some like a minnow and others not so good. The
species and most other Blue-winged Olives are swimmers. The
Isonychia bicolor, or Slate Winged Drake is a swimmer is a strong swimmer. The
swimmers are available for trout to eat most of the time.
Then there is the burrowing nymph that lives most of its life in burrows in the
bottom of the stream's soft soil or fine gravel. Most of these are the big drakes.
These are only available to trout some of the time, mainly when they come out
of their holes to eat or hatch.  
The clinger nymphs can attach themselves to a rock and live most of their lives
under rocks in fast water. They are only available to trout at certain times -such
as just before the hatch.
And finally there are the crawlers. For the most part, these are moderate water
nymphs but their habitat can vary quite a bit. Green Drakes are examples of
crawler nymphs. They are available to trout much of the time.
A swimmer mayfly nymph looks and behaves as much like a clinger nymph as a
deer looks like an antelope. A crawler nymph looks and behaves as much like a
burrower nymph as a moose looks like a buffalo.

You need to know which type of nymph you are imitating. Otherwise, to be
frank, when you are fishing a nymph imitation, you simply do not know what you
are doing - much less what it is you are imitating.

Copyright 2009 James Marsh