Story by Harvey Thommasen with Photography by Nick Didlick

Chironomids are the most common aquatic insects in our coastal freshwater streams, lakes, and ponds. In some streams, the larvae of chironomids comprise up to 80% of the total stream insect population. Chironomids are an important food for both growing fish and carnivorous aquatic insects. The fish eat them whenever they are available.

In early spring, the most common chironomids are Orthocladiinae spp and Chironominae spp. Flyfishermen do not need to identify chironomids to species, or even to genus because while there are many different species, they all look the same to the naked eye - tiny, black, two-winged insects that resemble little mosquitoes.

Though chironomids emerge year round, April to September is when they are most conspicuous. Look for the adult mating swarms over stream waters. Some of these mating swarms are large enough that one can actually hear the hum of their beating wings.

Though they look like mosquitoes, chironomids do not bite. In fact adult chironomids do not feed at all; their main job is to reproduce the species.

The mating swarms are composed almost entirely of males who are waiting for females who periodically enter the swarms in search of a mate. Once the mate is selected, the pair head off to the shelter of the surrounding vegetation to breed. Within a few days of mating, the females returns to the water to deposit her fertilized eggs. The eggs sink to the bottom, and begin to incubate. The male dies shortly after mating, the female dies shortly after depositing her eggs in the water.

The larval which hatch from the tiny eggs have a well developed head capsule, and a worm-like body with a number of true, and false 'legs".

These legs are used for creeping or crawling movements. Depending on the species, colour ranges from light cream, tan, brown, green, black, red, to shades in between. Length of mature chironomid lar vae are typically 1 - 10 mm (1/32 to 1/2 inch) long.

Favoured habitat is a muddy bottom. There chironomid larvae typically build simple tube-like shelters from which they feed on algae or decaying plant and animal matter. When fully grown, the larvae retreats into its tube-like shelter, constructs a pupal case, and then undergoes a transformation into adult form. Once this is complete, the pupa wiggles out of it's cocoon-like larval case, and then heads for the surface of the water.

This is when a classic angling opportunity presents itself. Fly fishermen dead drift chironomids, often on extremely long leaders, from a floating line.

The key to successful chironomid fishing is to match the hatch in size and colour - and then match the depth.

Although there may be adult chironomid emerging from pupal cases on the surface - and fish do feed on this life stage - the mass of chironomid larvae may be suspended at some depth.

Fly fishers learn to experiment, sometimes using 18-20 foot leaders, to reach the level where the fish are feeding.

One key to watch for, are the abandoned pupal cases, that can be seen floating on the surface the morning after a hatch. The presence of the cases indicate chironomid larvae are suspended somewhere in the depths, waiting for the right conditions to trigger another drift to the surface.

The fish will know where the chironomids are - and they will be feeding on them heavily.