Summary of Aquatic Insect Groups for the Fly Angler

Fly fishing is just a matter of tying on a fly of the right size when we see fish, such as a trout or a bass; feeding on similar-looking insects on the water’s surface. Knowing more about the identity, behavior, and life history of the insects that make up our target’s diets improves the odds that we fool those fish into taking our offering. The acquisition of this knowledge has for many anglers become a pleasurable end in itself, an integral part of fly fishing because it helps us to understand and appreciate the natural world of freshwater fish.

Although all insects will at some time be found in rivers or lakes, only eleven of the twenty-seven orders of insects are usually encountered by freshwater gamefish. This cuts down on the number of imitations we need to carry in our fly box to something less than the 750,000 species of insects described by scientists thus far.

River and lake insect orders can be easily divided into two main groups that entomologists call the Exopterygota and the Endopterygota. (see images)  


The first group of orders develop their wings externally (exo+ptera, for wing),


while the second group develop wings internally (endo). This distinction is useful for fly anglers because it separates all the flies with a pupal stage from those without a pupal stage.

Mayflies, dragon and damselflies, grasshoppers, stoneflies and waterboatmen are representative of the five Exopterygote  orders; beetles, alderflies, caddis, moths, midges, ants and wasps are the six endopterygote orders.

The exopterygote condition is a consequence of what is termed an “incomplete metamorphosis”, when the immature stages progress through slight incremental changes with each molt until the externally developing wings are complete and the insect flies away as an adult. If the adult as compound eyes, they are also seen in the immature stages. From the egg to the reproductive adult stage can require more than twenty stages, during which the insect is termed a ‘nymph’.

Many anglers carry a ‘nymph fly’ box and a ‘dry fly’ box so to separate floating flies from sinking flies. Imitations tied for flyfishing need to consider not only the size of the nymph but also any indicators that it might be approaching maturity and ‘hatching’, such as darkened wing pads, more prominent eyes, and a line along the back where the nymphal skin will split.  Mayflies have two flying stages: a sub-imago or ‘dun’ stage, and an imago or ‘spinner’ stage. The dun emerges from the nymph, near or at the water’s surface, and flies away.  It is not the mature reproductive stage at this time – it must shed its skin one more time, usually within 24 hours of emerging before returning and looking different, with longer tails, prominent eyes in the male, and clearer wings. At this stage the insect can mate and lay eggs on the water’s surface.

The endopterygote orders have a complete metamorphosis, with only a few fixed number of larval stages (i.e. Caddis flies have five larval stages). These larval stages (“stadia”) are caterpillar-like and are all similar within a species, except for the steady increase in size. At the end of the last larval stadia, the insect often constructs a cocoon in which it pupates; complete changes in development and appearance occur. Internally forming wings, genitalia, and compound eyes appear, and the adult insect that emerges looks almost nothing like the larval stages. Fly anglers must imitate larvae of different sizes, an emerging pupal stage, and the adult. Most insect larvae are poor swimmers, but the pupal stage may be optimized through evolution, for a rapid transition to the adult stage to lessen the stage of being eaten. Pupae of some species, such as Caddis can be much more adept swimmers than they were at the larval stage. Adults emerge from the pupal skin and are ready to mate as soon as their cuticle has hardened, with the exposure to air.

Many details of insect biology are unique to particular orders or even species; all may be used by fly tiers to aid in designing appropriate imitations to “match the hatch” or having the right meal at the right time.

Fly anglers don’t need to know scientific names. You won’t be tested on the names of insects when meeting another angler on a river. Just look around you and ‘match what you see the fish taking, with something in your flybox.

The first thing you want to match is to have something that looks like the live insect, even if its not the same color. Next, try and match the size, then finally, you can try and find the color. Or, refer to your hatch chart for the particular river you’re fishing.

Our hatch charts are less than 5 years old, because the editors of the website are avid anglers and we fish the rivers we create hatch charts for all the time, take notes on what’s hatching, what works, and what doesn’t. For instance, in 2020 I fished Schoharie Creek (actually one of my favorite rivers not far from here) in April, May and September, each time in a different part of the river. In 2021, I fished it in May and June, and again at the end of August. In 2022, I fished it in April, May, and June. I’ve got one of those little voice recorders, and I talk a lot of notes, then when I come back from my trip, I’ll assemble the notes into data. You can do this as well. Just buy a little notebook for a particular river read the page on this website about keeping journals.