Entomology for beginners

By Bruce Tait

Most fly fishing is based upon imitating the foodstuff of our quarry. For the river angler this predominantly means imitating insects at various stages of their life cycle. To be able to do this we need to be able to identify the insects and have a basic knowledge of their life cycle.

It is not necessary however to fully understand all the groups, sub groups and classes or to be able to identify them by their Latin names. What is important is to understand the basic types and at what stage in the life cycle the fish are taking them.

The following is a brief introduction to the basic fly types, including a fly calendar to show when during the year we can expect to see them and hence when a suitable imitation should reap rewards.

MAYFLIES: UPWINGED FLIES (EPHEMEROPTERA)

Characteristics

Two large upright transparent or opaque wings

Two or three long tails

A segmented body and a thorax

Almost all have two small hind wings

Examples
Mayfly (Green drake)
Blue winged olive
Large dark olive

Life cycle
All upwinged flies go through a four-stage life cycle

Egg –> Nymph –> Dun –> Spinner

The first two stages are underwater while the last two are the adult winged stages.

There are various forms of nymphs and these are generally classified by how they behave:

Burrowers: Live in tunnels in the mud, sand and gravel on the river bed eg, mayfly nymph

Silt crawlers: Tiny nymphs which crawl along the silty beds of rivers eg, caenis

Stone clingers: Spend most of their time on the undersides of stones and are rarely seen swimming around, eg, March brown nymph

Moss creepers: a group of weak-swimming nymphs who feed on mosses on the river bed, eg, Blue winged olive nymph

Laboured swimmers: Spend most of their time in the margins but can swim from place to place, eg, Claret nymph

Agile darters: Swim freely and rapidly from place to place and are therefore available for fish to feed on, eg, Dark olive nymph

SEDGES: FLIES WITH ROOF SHAPED WINGS (TRICHOPTERA)

Characteristics

• Four wings, with the front pair usually being longer than the rear pair
• When at rest the wings lie close along the body in an inverted V shape
• No tails
• Look similar to moths but have a coating of fine hairs on their wings whereas moths are coated in tiny scales

Examples
Sedge or Caddis

Life cycle
Sedges also have a four-stage life cycle; however it is different to that of the upwinged flies

Egg –> Larva –> Pupa –> Winged adult

The majority of the larvae live in cases which they construct from materials found on the river bed such as grit, sticks, leaves etc. The remaining larvae are free swimming.

Examples of free-swimming larvae
Rhyacophila larva
Hydropsyche larva

FLAT WINGED FLIES (DIPTERA)

Characteristics
• Two short transparent wings which mostly lie flat along the top of the body
• No tails
• Two of the most common species of this group are the house fly and mosquito

Examples
Midge
Hawthorn fly

Life cycle
This is a large group and many have a life cycle which are land-based and therefore not of interest to the angler. Only the adults which are blown or drop onto the river will be of interest. There are however, two members of this group that do have aquatic life cycles and are therefore of interest: these are the Reed smuts and the Midges. The reed smuts are tiny black flies and almost too small for the angler to imitate.

The midges are slightly larger. Their life cycle is:

Eggs –> Larva –> Pupa –> Winged adult

The larvae are worm-like and vary in colour from pale green through to bright red.

STONEFLIES: HARD WINGED FLIES (PLECOPTERA)

Characteristics
• Four wings which are hard and shiny
• Wings appear very narrow when the fly is at rest
• Wings lie flat along and slightly over the body

Examples
Willow fly
Needle fly

Life cycle
Stoneflies have a three-stage life cycle:

Egg –> Nymph –> Adult

The nymphs have two tails and quite long antennae. The mature nymph crawls to the shore or finds a convenient rock or post to climb out of the water where it emerges into the adult. During this migration it is particularly vulnerable to the trout.

FLY CALENDAR

This is a general idea of what you would expect to see on the River Derwent. Timing is deliberately vague as a number of factors will influence the hatches, including river and weather conditions.