From the flyfishing perspective all aquatic insects are created equal. Fish will eat virtually any aquatic insect at any life stage but that does not mean flyfishers appreciate all of them.
If you strip away the flyfishing mystique of fancy equipment, well meant advice and the blizzard of "guaranteed" fishing equipment; you are left with the true art of fly fishing: illusion. Both the practiced magician and the flyrodder foster their illusions with props. Flyfishing props are tiny bits of fur, feathers and thread fashioned on a hook to create an imitation of an aquatic insect that looks sufficiently real to fool a fish. Some of these insects are beautiful to behold, others bite.
One biter you swat is the mosquito. The word mosquito is Spanish meaning little fly and it has been around to worry warm and cold blooded animals for 80 million years. There are 3,500 known species of mosquitoes. Nymphal mosquitoes called wigglers are found in slow moving and stagnant waters doing their twitchy little dance that carries them between feeding on algae, bacteria and other micro-organisms in the water column and then up to the surface to breath air through their siphon. Wigglers hang upside down when breathing since the siphon is located on the last segment of their body. Once they hatch out into adults they can be a bother to flyfishers on or off the water but they are a go to imitation when there are no other insects on the water.
And then there is that most robust biter in the North Country, the black fly. The black fly is a member of the family Simuliidae. There are over 1,800 known species of black flies and they have been around at least for 2.5 million years. Black flies emerge as just one or multiple generations in any given year depending on the species and/or the human efforts to control these insects. In some cases if one generation is killed off another develops to fill the void.
Adult winged black flies are small, dark flies with a humped back. The female can give a painful bite when they slash our skin and lap up the pooled blood. It was a bit disheartening to read that DEET-based insect repellents attract greater numbers of black flies. Based on personal experience though, black flies seldom bother a flyfisher standing in the middle of a stream. The warm blooded black fly prey is on the land, they know it and once hatched make for the shore.
Black flies are an indicator species. They thrive in streams with clean, clear, cold, well-oxygenated, unpolluted water. While mosquitoes, deer flies and horse flies tolerate warmer ponds and wetlands including brackish tidal marshes, black flies require cold oxygen rich water to nourish eggs and larvae that live underwater for a year before getting their wings. You swat black flies but these pesky insects are harbingers that more fisher friendly insects called mayflies are about ready to appear on the river.
As rivers awakens from winter, warming water prompts aquatic insects to metamorphose from their nymphal underwater life form to the adult winged stage. Once conditions are right all the individuals of a mayfly species "hatch" in a defined window of time lasting days to weeks long. These hatches can be timed with the seasons with a progression from the early Iron Fratador through the spring Hendrickson to the summer Trico to the fall Blue Wing Olive.
Many of the most delightful mayflies belong to the order Ephemeroptera meaning "short-lived with wings" accurately describing the short life span of the adult that can vary from just 30 minutes to at most a few days during which the adults perform a mating flight above the stream. The female deposits eggs by delicately fluttering up and down touching the stream and with each touch dropping eggs to start the regeneration of the species. The eggs sink to the bottom and will hatch into a crawling underwater nymph. This stage may last from months to years with a number of molts along the way.
The habitat of mayfly nymphs is under the rocks at the bottom of a stream filtering out microscopic food and oxygen. Fish feed on mayflies in that brief period of time either while a nymph drifts or swims to the surface to emerge from their nymphal case or while the newly emerged insect sits on the surface waiting for its wings to dry and harden so it can fly off and complete the only mission of the adult and that is to mate and produce the next generation.
Imitations can be made for any of these insects in most of their life stages. So a flyfisher on stream might have to swat a few insects now and again but fished properly and with a wee bit of luck these props will fool a fish.
David Deen is River Steward for the Connecticut River Watershed Council. CRWC has been a protector of the 4 state Connecticut River watershed for more than half a century.