Chironomids belong to the insect order Diptera and are characterized by a four-stage life cycle. This is complete life cycle, which consists of the egg, larva, pupa and adult. The cycle starts when a female lays eggs during the early morning or evening hours when the waters surface tends to be calm and the risk of predation from birds and other insects is low. The eggs drift down to the bottom were they soon hatch into the larval stage.
Capable of surviving in a diverse range of habitats and conditions chironomids are found in bogs, lakes, ponds, rivers, and streams. You will find them in the tropics and all the way to the Arctic. They are one on mother natures most hardy insects. Their preferred aquatic environments feature soft stable bottoms and weeds, traits of slow moving stretches, spring creeks, tail waters, lakes and ponds. Here in western North America productive mud bottom lakes are home to a staggering number of chironomid species, many capable of attaining large sizes. They can obtain sizes as close to an inch in some instances, which is quite a but larger than most people realize. This is a definite contradiction to their midge moniker.
Depending upon the chironomid species and habitat they are found in a wide range of sizes, from too small to imitate to the big "extra large" chironomids of the west, as mentioned larva can reach to a size that is close to an inch in length. When you find them in rivers and streams they often of smaller sizes due in part to multiple generations. Species capable of more than one hatch cycle per season are often smaller as a result of less growing time between hatches. Multiple emergences are common in southern latitudes and warmer water temperatures.
On the opposite end of the spectrum, some species feature one year cycles and are typically large. Because of this pattern choices can range from as small as #24 to as large as #16. Depending upon your region, stillwater fly boxes will often feature larger sizes, #18 to #6 in some cases. Clear water lakes and ponds tend to feature smaller sizes while rich mud bottom algae type lakes are ideal habitat for the larger species.
Most fly fishers overlook the importance of the chironomid larva. Maybe its because of their slim nature, perceived small sizes or the fact that majority of species live out their larval existence burrowing and writhing about in the bottom ooze. Trout don't have the same opinion and are finely tuned to the intrinsic food value of chironomid larva.
Chironomid larvae grow through 3 to 4 instars. Within species there is a downsizing between stages, a trait common to many insects. Larvae are larger than pupae which in turn are larger than adults, a key consideration when choosing patterns during an emergence.
In the chironomid larval stage, only the free swimming larva (Bloodworm and Glassworm) are normally found in the feeding samples of the rainbow trout. This is also very important vent selecting larva patterns. The typical size range for most stillwater larva or bloodworm patterns ranges from size 8 2xl down through size 16 standard. The use of a throat pump when fishing will help determine the size of the larva that the fish are feeding on. You have to catch one first of course.
Chironomid larvae are present in a wide array of colors. The most popular schemes include brown, medium green, olive, maroon and red, the red larvae have been christened by many as "bloodworms." The distinct red coloration is a result of hemoglobin that many species use to survive in oxygen poor waters. A certain times of the year such as the middle of summer oxygen levels in lakes drop as a result of increasing water temperature. Larva use iron molecules in their red blood cells (hemoglobin) to bind and carry oxygen. Later in the season as the oxygen levels return to comfortable levels the larvae return to their natural green and olive colorations. During this transition period it is not uncommon to see unique candy cane colored larvae of red and green. Keep some of these 'candy cane' patterns in your fly box to take advantage of these occasions. Other color considerations include olive, green and a unique candy cane combination of red and green.
Phil Rowley has a fantastic book titled "Stillwater Selections" that has many "Go To" chironomid larva and pupa patterns.
Where the Larva Live, their Habitat.
Most species of chironomid larva, and there are over 2500 chironomid species in western North America alone, construct tubular homes in the mud water interface along the bottom. Within the safety of their homes the larva pulse their worm like bodies to draw detritus and other food sources into their tube. Feeble swimmers, the larvae move through the water with a lashing head to tail motion reminiscent of a severed worm. Despite this handicap larva often leave the sanctuary of their homes to forage and migrate. Spring and fall are two such times for these migrations and larval patterns should be primary considerations. During low light hours chironomid larva often venture out for a feed making a bloodworm pattern a favored lead off hitter. Plying the waters after a good windstorm with larval imitations is another wise strategy as many larvae are swept from their homes by the swells and aggressive wave action.
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.
The worm-like larva are a year round food source or staple as important as the more famous staples that includes scuds, dragon nymphs, damselfly nymphs and leeches. In the absence of a hatch imitating a stillwater staple of some sort is the way to go. In the early morning hours many food sources are active, foraging under the relative security of the low light conditions.
Chironomid larvae venture out of the protective tubes many species construct in the mud water interface. Feeble swimmers chironomid larva writhe and wriggle about at the mercy of the elements, foraging upon detritus and decaying vegetation. Opportunistic trout cruise above tipping head down to vacuum chironomid larva from their mud tubes and those left wandering too far from home. During intense windstorms many larvae are swept from their homes and dashed amongst the weeds. Using the ambient wind to sweep or wind-drift a larval imitation on a floating line and long leader (15 feet plus) can be lethal. Any time an angler sees chironomid larva adrift in the water column try sweeping a larval imitation using this wind-drifting tactic. Wind drifting is an excellent tactic to cover water with a near static presentation.
As with many insect larva and nymphs in stillwaters bloodworms migrate on a seasonal basis. In the spring larva migrate into the shallower reaches and reestablish their tubular homes. During the late fall those larvae not mature for their transition to the pupal stage travel to deeper climes to escape the harsh temperatures and ice of winter. Matching presentation techniques to simulate the natural travel of aquatic invertebrates is a sound plan.
The stillwater fly fisher should use the same presentation techniques that have been refined for the pupal phase of the chironomid life cycle. The key is keeping the offering near the bottom, within one to two feet. Strike indicators are of great assistance to novice fly fishers struggling with the confidence to fish a pattern that reassembles a tiny red stick in the vast expanse of a lake.
Chironomid Pupa Life Cycle
Chironomid pupa are a year round food source and a regular feature on the trout's menu making them the number one food source for trout in stillwaters.
When chironomids enter their pupal stage they are at their most important point of development from the perspective of 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.
Depending upon the species chironomids can spend up to 1 year in the larval stage. The larva seals itself within its tube or constructs a temporary home to transform into the pupa. During this transformation the larva develops wing pads and a distinct thorax. When the time is right the now transformed pupa cuts its way free and prepares for its journey to the surface to emerge. Once 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 stop their upward progression and are stationary, suspended between lake bottom and surface. Many anglers are mistaken and believe that the pupa rocket to the surface without stopping. The real story is that the move to the surface in stages and often hover near the bottom. These hovering pupa can take up to 4 days to ascend so trout have ample time to feed on them. This explains why fishing pupal patterns can be deadly while there appears to be little evidence of an impending hatch at the surface. The trout are busy feeding on the bottom. Figuring out what depth the trout are feeding at is the key to chironomid fishing. Remember this!
During this staging process the chironomid pupa absorbs air and gases under its pupal skin. Starting off as a dull almost gun metal sheen these air and gases turn the pupa to almost silver as the emergence process nears the end. These trapped air and gases often obscure the pupa’s natural coloration and during the pupal ascent its color can change and vary in intensity. Common pupa colors include black, maroon, olive, brown and various shades of green.
Adults closely resemble pesky mosquitos. Fortunately chironomid females possess no piercing proboscis. You won't be troubled by bothersome bites. Adult chironomids have slender tapered bodies similar to the pupa no tails and a pair of wings that trail back over the body when at rest. The thorax area is humped and they often feature prominent eyes. Males are easily be identified by their plumose antenna is used to aid their search for a mate. Females on the other hand display fine difficult to see antenna.
.Adult coloration varies little from the pupa, upon emergence however adult coloration tends to be brighter until their bodies harden. Trout preying on adults in selective situations can become color sensitive and brighter, recently emerged adults still unable to take flight until their bodies and wings harden are easy fare.
Once emergence is complete adults fly off to shoreline areas. Most adults do not feed and this stage is short lived, just long enough to propagate the species. Males form large swarms resembling dust clouds along the margins. Large concentrations of adults are audible from a distance and create a high pitched buzzing sound. Hence their English nickname, "buzzers". Males release pheromones to attract a mate. Mating takes place in the air or on the ground. During low light conditions when the water is calm on stillwaters and the risk of avian predation is reduced egg laden females return to the water to deposit their eggs. Females skate across the surface speed boat style or dive below to lay their eggs. Skittering females draw trout to the surface providing anglers dry fly opportunities. Adults often form huge mats on the surface and on rivers and streams collecting in calms and back eddies. Trout move into these areas sipping adult clusters with slow deliberate rises. Patterns such as the Griffiths Gnat are good choices in these conditions. Many times it is difficult to tell if a trout has taken the fly. Get into the habit of using the fly line as site and lift the rod smoothly if a rise occurs near the fly. It is surprising how often the rise is to the fly that otherwise would have gone unnoticed. This tactic has paid dividends on numerous occasions.