Identifying Trout Stream Insects

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

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.  
Copyright 2009 James Marsh
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