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Entomology

Blood Midges

A bloody big bite


The dead zone. So utterly dead that corpses barely rot. They linger in the dark and the cold; soft lumps of meat delicately smothered by an ever-thickening blanket of silt and slime. The zone can be black or brown or grey; it is never green. What sunlight might penetrate here has been sucked dry of its life giving energy and plants don’t survive. Without plants, the process of photosynthesis can’t charge the environment with oxygen, and without oxygen, the dead zone is complete.

Limnologists identify the dead zone as the hypolimnion. The waters of the hypolimnion are so dense that the currents of the warmer, lighter, oxygen rich environment overhead don’t mix. On the lake’s surface it can be Victory at Sea, but in the dead zone not a wisp of silt will reflect that turbulence. When plants and animals die, their bodies drift through the warm, biologically active zone (the epilimnion), break through that abrupt shift in temperature known as the thermocline, and continue their downward plunge into the cold, dark and still.

The dead zone is a niche harboring a limitless source of nutrient and is devoid of predators. Any organism that could exploit the zone would thrive in extraordinary abundance. And one creature does just that.

The Chironomidae is one of several families of midges. Members of this diverse family are better known to the angler as Chironomids. Among the Chironomids is a subfamily called Chironominae; these guys are the blood midges.

Blood midge larvae

 

Chironominae larvae are brilliantly red and if inadvertently squeezed will burst like a pricked blood blister. This "blood" is red because it is loaded with hemoglobin, the same stuff that makes our blood red. Hemoglobin has a profound affinity for oxygen and the tremendous density of hemoglobin in the midge’s blood allows it to thrive in environments nearly devoid of oxygen; environments like the dead zone. The blood midge larvae burrows into the muck where they undulate for minutes on end. This writhing motion stirs the water around and whatever tiny amount of oxygen might be available becomes fixed to the hemoglobin. When the insect hemoglobin (more correctly termed 2 heme, high affinity hemoglobin) becomes saturated with oxygen, the midge larvae rests to feed on the nutrient rich slop in which it resides. At this point the larvae can survive in a completely oxygen free environment. When the oxygen stores are depleted and the larva enters into anaerobic metabolism, the midge once again commences its oxygen scavenging dance.

Limitless food and no enemies. These guys have it made in the shade. The only downfall might be lack of privacy. The living is so cush that thousands, no, tens of thousands of midge larvae live shoulder to shoulder. Densities of 50,000 larvae per square meter are not uncommon. This is a good thing if you’re a flyfisherman.

Blood midges abound in all mud bottomed lakes but are most prolific in the alkaline lakes of the Western US and British Columbia. In lakes that have an abundance of baitfish, blood midges are frequently the most important dry fly on the water. Many lakes, such as Martis, historically had huge callibaetis hatches, but the introduction of voracious trash fish quickly thinned the mayfly populations. The blood midges continue to thrive unmolested in the dead zone.

After a few weeks or months (there is huge discrepancy amid members of this group, and environmental factors such as temperature and water chemistry influence growth) of groveling in the slop, the larva enters a period of pupation. The pupa matures quickly, frees itself from the mud and swims in a squirming fashion towards the surface. The puparium is filled with gasses that give the pupa buoyancy and help its ascension. For the first time in its life, the midge enters the world of predators.

The gas filled translucent pupal sheath backlit by the relatively bright sky turns the pupae into shimmering orange sparks. The effect is extraordinary. Standard pupal imitations look like someone’s idea of a bad joke. A brassie gives off a coppery shine that appears lifeless next to the real deal; however, as traditional imitations go, it’s much better than most.

I personally like a thinly dubbed body of bright orange Antron (Umpqua "crayfish") ribbed with copper wire for weight. I treat this with powdered floatant to encase the bug in a flashy, transparent bubble. The pattern doesn’t look good enough to sell to humans so I don’t try. I tie it for myself and sell it to my finny consumers. They pay with tugs.

The ascending pupae finally bump up against underside of the lake’s surface film. This film is like a rubbery skin and the job of the pupa at this point is to punch a hole through this skin to create nothing less than an escape hatch for the adult midge. I’ve watched pupae bounce repeatedly off the tough skin until the head finally breaks through.

The pupal skin (exuvia) splits at the shoulders and the adult midge slowly squirts out. As the adult emerges, the tube-like exuvia reveals itself to be almost colorless; very similar to the plastic wrapper that contains a drinking straw. Invariably there are a few tiny bubbles in the sheath and they, along with the transparent membrane itself, sparkle in the back lit sky’s light.

Only after most of the adult has wriggled out do the legs pull free and settle down on the water. The whole effect is very smooth, delicate, and efficient. Compare this with a mayfly that emerges by dragging itself out of the opaque and messy nymphal exoskeleton by clawing with its feet against the surface tension. From a trout’s vantage, a mayfly emerger and a midge emerger are as different as night and day.

The emerger is the life stage most vulnerable to predation. The larvae, of course, are immune to predation because they live where fish can’t. The ascending pupae are eagerly eaten, however, since these guys are scattered throughout the water column, it is relatively inefficient for trout to graze on them. At the surface, all pupae stall out in a single strata and it is here that trout congregate to feed.

Some trout key in on the pre emergent pupae and a few seem attracted to the recently freed winged adult. Most fish however, want the emerger, and few trout would ever pass one by.

Martis Lake, a profoundly rich blood midge (and trout) habitat near my home became the laboratory for my efforts to create the better blood midge emerger. The result was the Martis Midge. It kicks butt if I don’t say so myself. Tie on a couple strands of pearl flashabou so they dangle beyond the bend of a size 14 or 16 dry fly hook. We only want to create the illusion of the transparent, sparkly trailing exuvia, anything more is counter productive. About the worst possible material for a midge shuck is the opaque marabou found on so many patterns.

The Martis Midge, a blood midge emerger imitation

Make a thin, non-tapered body of Umpqua’s "crayfish" Antron dubbing two third’s the way up the shank. Tie in a slender post of bright orange elk so that it doesn’t flare and so that it extends over the eye of the hook at a 45° angle. Finally, make two or three wraps of furnace hackle at the base of the post in the traditional, non-parachute style.

Treat the fly and leader with floatant then heave it and leave it. If fish are rising to midges around yours but won’t grab, trim (gnaw) the elk hair down to just a nubbin. At times they selectively want the pre emerger and that’s what you just made.
Blood midges seem to stir the proprietary nature in people; everyone wants them for themselves. I’ve heard them called the Crane Prairie midge, the Crowley midge, the Hebgen midge, the Tunkwa midge, and even the Martis midge. By any name, it’s a bloody good insect.