Midges & Crane Flies ( Aquatic Diptera)
The subject of aquatic Diptera is vast, fascinating and much too comprehensive to treat here, except in a most general manner. Most Diptera are not associated with trout waters but are slow water species of the warmer climates. Thus we will limit our discussion to those that seem to important to the diet of the trout: midges and crane flies. Proper classification of suborders, families, subfamilies, and so on will not be attempted.
The larvae of the Diptera, wormlike and legless, live under or attached to stones, in the muck where they build tubes, and in vegetation ( depending on the family or genus). They feed on algae, plankton, and detritus. Generally, the larvae of mideges and crane flies are herbivorous, although some of the large crame fly larvae ( which may reach 3 inches in length) are carnivorous and can consume mayfly nymphs and even stone fly nymphs.
Like caddis flies, Diptera have a complete metamorphoisi a four stage life cycle; egg, larvae, pupae, and adult. The egg, larval, and pupal stages are generally passed underwater, although some larvae migate to stream banks to pupate. The larvae may mature in a few weeks or take as long as two years. Most trout stream species haver several broods per season.
The adults are two winged, as denoted by the Diptera; the hind pair of wings, reduced to club shaped balancing organs, are called halteres. Most species are equipped with mouth parts adapted for sucking liquids, and most adults ar nonbiting, but those from some famileis such as simuliidae (blackflies) and Heleidae (punkies) can inflict painful bites, as most fly fishermen can attest.
The presence and relative importance of the various species within familie will vary greatly from one trout stream to another, according to specialized habitats. We have foun, however, that with few exceptions there are only a limited number of families of midges and crane flies that may be important enough to cause selective feeding by trout, especially brown trout, which are the most efficient of selective feeders in the trout family. Even these limited Diptera types are usually important only on sluggish headwaters and on silt laden meadow or farmland streams, or perhaps on long, flat stretches or quiet pools of mountain rivers.
The larvae of the shallow, swift water species such as those of the simulium (blackfly) Blepharocera (net winged midge), and Palpomyia (punkie or no see um) genera seldom prompt selective feeding by mature fish, b ut young trout's as well as bait fish feed on them often.
Chironomidae species, which number in the thousands are nonbiting midges. The adults range from 2mm in size to almost 1 inch, but the most common are the tiny midge forms, approximately 3 to 6 mm size(28 to 18 hook). The colors of the larvae range from white to red, and to gree, brown, and black. The red larvae are called bloodworms and owe their color to a respiratory blood pigment that enables them to exist in streams of low oxygen content. Most of the larvae mix saliva with silt and sand to construct openeded tubes on the bottom. Like caddis flies, they spin a net across the tube opening that filters plankton and detritus matter. Pupation usually takes place in the tube, and thus they are virtually inaccessible to trout during the larval stage.
The pupae come to the surface to emerge; there they may hatch immediately or hang suspended for a short while. Like the other insect orders, this vulnerable period varies within the species or according to the water and air temperature. A surface ruffled by winds may also cost the emerging pupae precious time. We have witnessed heavy feeding to the pupae and crippled adults on silt ridden streams and headwater bogs during thes emergences.
The same waters can produce selective feeding to the large Diptera forms of the family Tipulidae, commonly called crane flies. These larvae can reach lengths up to 70 mm, but the size range is usually 10 to 50 mm. Most crane margins. Some live in wet meadowlands and pastures, and thes forms are obviously not important to the trout's diet. A few geera, however, suchas Antacha and Hexatomia, are wholly aquatic.
Owning to the vast number of species, and size variances within, the midge and crane fly families are very difficult to anticipate and prepare for , as far as fly tying and the emergences are concerned. Thus anglers should record any activity that may have caused selective feeding by trout, so that they can return to the river better prepared the next time.
by; Caucci and Nastasi
Masters on the Nymph
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