Chironomids

Chironomids are abundant in our rivers, lakes, ponds, and streams playing a significant role in the aquatic ecosystems and prey for the trout.  They are often diminutive in size range, simple physique, and a challenge fishing them during wintry months.  Chironomids are a type of aquatic insect belonging to the family, Chironomidae, and from the order Diptera translating as two (Di) winged (ptera) indicative to the winged adult stage.  From the perspective of fly fishermen, chironomids represent a beneficial food source prominently during the winter fishing season.

Studying this midge under microscope from a water sample I collected.

Chironomids have a complete lifecycle metamorphosis of larva, pupa, and adult.  The chironomid larva grow through 3 to 4 instars, or developmental growth stages. Starting from the egg stage, the midge larva are then worm-like, slender bodied, and often called bloodworms red in color due to hemoglobin within their iron-based blood system.  They have 9 body segments and little, stubby legs.  Chironomids are important decomposers and contribute to the nutritional cycle in the freshwater ecosystems.

The Paisy Midge I tied in studying this midge under a microscope.

The pupal stage is characterized by more definitive features, including slim, tapered, and segmented bodies.  Their thorax is distinct and bulbous, featuring wing pads, while the legs and antennae trail beneath the thorax.  Pupae exhibit a diverse array of colors, ranging from olive and tan to shades of green, black, brown, and maroon.  This growth transformation occurs before the emergence of the insect as an adult.

A midge I collected from the river.

The adult stage represents the winged and reproductive phase of the insect’s life cycle.  Resembling like mosquitoes, adult chironomids possess slender, tapered bodies compared to the pupal stage, lacking tails, and have a pair of wings trailing back over the body.  Their thorax is humped, and they typically accentuated with noticeable eyes.  Male chironomids are distinguished by their plumose antennae, which helps them in seeking out a mate. Females, on the other hand, exhibit a finer, more indistinct antennae.  Adult midges swarm, mate and return back into the water.  Female midges typically lay their eggs by scattering them along the water’s surface as they fly low over the water, or underwater along the river bottom.

My Matchstick Midge fishes incredibly well on the S. Platte River.

Pupae ascend and undulate slowly through the water column until they reach the surface, where they undergo their final transformation into adults.  Upon reaching the surface, they momentarily suspend before adopting a horizontal posture.  A split emerges along the back of the thorax, and with the aid of trapped air and gases, the adult emerges in front of the discarded pupal shuck.  These cast shucks often retain the distinctive white gills near the head of the insect.

Pat Dorsey's amazing Black Beauty.

Once the emergence process is complete, the adults soar in the air and migrate to shoreline areas.  The adult stage is typically brief, as most adults do not dine, but instead focus on reproducing.  Male midges form swarms like dust clouds along the water’s edge.  These swarms release a high-pitched buzzing sound.  Males release pheromones to entice mates, and mating will occur either in the air or on the ground.  During low-light conditions, when waters are tranquil, and the risk of predator is low, egg-laden females return to the water to lay their eggs.  Females will glide across the water’s surface, or divine below the water to lay their eggs.  Adults so thick, they form mats on the water’s surface and accumulate in calms and back eddies of rivers and streams.  The hungry trout are drawn to these areas and found delicately sipping adult clusters.  Happy fishing!  See you on the rivers!

Happy fly tying and fishing chironomids!