CHIRONOMID

article by Ron Newman

Scientific Name:

Class-Insecta, Order-Diptera, Family-Chironomidae. (Over 2000 species)

Common Names:

General

Small two-winged flies in the adult stage. Closely related to mosquitoes and Chaoborus (Phantom Midge or Glassworm). However, mosquitoes do not normally live in our lakes due to wave action and Chironomid do not bite like mosquitoes. Due to their similarity, the Chaoborus will be included in this discussion.

Life Cycle:

Adults swarm and mate in flight. Most lay eggs singularly or in strings while skimming over the water surface. Some species lay eggs directly on vegetation or bottom substrates. The eggs hatch into larva and form mud tubes from bottom material and mucous. A few species have free swimming larva such as the Bloodworm and Glassworm. The larva grow and develop into the pupa stage. When fully developed, the pupa wiggle their way to the lake surface. It often takes several minutes for the pupa to get through the "surface tension" of the water before it can hatch. The process of breaking open the pupal skin, the adult crawling out, drying its wings, and flying away is usually accomplished in less than a minute. Once hatched, the adults may live from a few hours to a couple of months before mating and dying.

Appearance:

The larva have segmented bodies, are worm-like and look much like a long skinny grub or maggot. This appearance gradually changes as they develop into a pupa. The pupa develop an eye-spot and wing casing and most notably have feathery white gills near the head. The head and wing casing are usually one quarter to one third of the body length and the abdoman has 7 or 8 body seqments. Adults look like a mosquito with feathery antenna.

Size:

Pupa are up to 20 mm long ( � inch) but average about 8 to 15 mm ( � to � inch).

Colour:

The pupa tend to be black, brown, reddish-brown or green but can come in a variety of other colors. Larva tend to be cream colored or may have a greenish tinge. There is a type of free swimming Chironomid larva that stores oxygen in it's blood and is thus blood red in color (Bloodworm). A free swimming larva of the Chaoborus family is virtually transparent (Glassworm).

Movement:

Free swimming larva like the bloodworm, do just that. They crawl, float or swim around the lake but generally tend to hide under rocks or rotting logs and remain fairly immobile. Most larva build and stay inside a mud tube on the lake bottom and don't move very far from that. When the larva develop into pupa they leave their mud tubes or hiding places, fill air sacks within their skin for buoyancy, and slowly wiggle their way to the surface to hatch. Often during this process they are stationary, suspended between lake bottom and surface. As adults, Chironomid fly over the water surface laying eggs and sometimes land on the water surface.

Habitat:

As long as they can get a food supply, Chironomid larva will live in almost any type of water. Clear or polluted with bottoms that are muddy, rocky, weedy or sandy doesn't seem to matter. However, their food source is generally most abundant on or near shoals and this is where their numbers peak. The preferred food seems to be Blue-Green Algae. The fecal pellets of Chironomid which have been feeding on Blue-Green Algae is the major component of 'Marl Shoals'. These are very similar to the oil forming shales. The adult and pupa of the Chironomid don't feed.

Importance to Fly Fishing

After freshwater shrimp, Chironomid are the next most important food source for the Kamloops Trout. Throughout the fly fishing season, daytime feeding samples show that 27% of the trout's daytime feeding consists of Chironomid. This drops to 14% for those fish feeding in the evening or at night.
Of importance is the fact that Chironomid are much more significant as a daytime food source. I suspect the 14% for the evening to night samples is a bit high. Some of those samples have probably included fish that were also feeding during the daytime.

Larva:

In their larval stage, only the free swimming larva (Bloodworm and Glassworm) are normally found in the feeding samples of the rainbow trout. Most other larva tend to stay in their mud tubes on the lake bottom and thus are of little importance for imitating with flies. Due to it's transparancy, the Glassworm is almost impossible to imitate with a fly and thus looses importance. However, Bloodworms total to 3% of the trout's diet and shouldn't be ignored. Retrieve the Bloodworms much the same as you would a Chironomid pupa and in the same types of water.

Pupa:

Chironomid in the pupal stage are at their most important point of development for the fly fisher. When leaving the bottom of the lake and traveling to the surface to hatch, they are most vulnerable to predation by the trout. Even the largest trout will actively feed on these pupa and they are successfully fished throughout the year.
Chironomid pupa should be fished on a dry line and the flies should be weighted. The retrieve should be very, very slow or even still. Vary your leader length to achieve the desired depth for the fly. The pupa can be found at most any depth in the lake but the trout will feed on these more actively on the shoals and drop offs. The colour and size of the fly seem to be more important than whether the flies have ribbing or gills. Flies with or without the gills and/or ribbing seem to work equally well.
Here is a hint that most fly fishers haven't yet picked up on when tying flies to imitate the Chironomid pupa. Make the bend and point of the hook appear as the tapering abdomen and tail part of the pupa rather than something the pupa is attached to. It will look like the pupa is in the curled position for wiggling to the surface. This is one of the few flies on which you can totally camouflage the hook.

Adults:

Chironomid adults, or when they are emerging into adults, are taken throughout the year by the rainbow trout. Most any of the very small dry flies will do as an imitation. Although taken by the trout, the adult Chironomid is taken much more actively by the smaller fish than the larger fish. When presenting the adult, try to get an 'S' shape in your leader (or even an arc) and retrieve with a long, slow, steady pull to imitate an adult skimming the surface laying eggs. Letting the fly just sit on the surface also works. For an emerging Chironomid, try tying an un-weighted pupa but where the gills would normally be tied, insert a clump of deer hair (or other lighter coloured floating material) of about two-thirds the pupa length.

Hatches:

Various species of Chironomid hatch whenever there is water free of ice. Seasonal peaks occur from the third week in May to the second week in June and then steadily decline into the fall months. However, very large hatches of individual species can occur at most any time of the year. Chironomid larva on the lake bottom will sometimes exceed 50,000 individuals per square metre and thus form 'major' hatches. . If you are fishing in a 'major' hatch, use a fly that is slightly larger than the actual size of the pupa. For the fly fisher, minor hatches often result in more fish than a major hatch. Hatches usually occur during the daylight hours but various species will hatch at night.

Recommended Fly Patterns:

Be sure to read other articles by Ron Newman