The dietary requirements of aquatic insects varies from species to species.

Aquatic insect larvae and nymphs which graze the stream bottom by scraping their mandibles over the stones and peeling away and eating minute plant organisms - diatoms and algae - are called grazers or herbivores. In general aquatic insect herbivores are found in faster flowing waters of a stream; in the rapids, riffles, and glides.\

Among the mayflies, the best known grazers are the Heptageniidae (ie Cinygma spp, Cinygmula spp, Epeorus spp, Rithrogena spp), the Baetidae (ie Acentrella spp, Baetis spp, Callibaetis spp) , and the Siphlonuridae (Ameletus validus).

Among the stoneflies, the Giant Stonefly (Pteronarcys californica) and the Little Black Stoneflies (Capnia spp, Isocapnia spp) are among the most obvious grazers.

Grazing caddisflies include the Microcaddis (Agraylea saltesea) , the Grannon Sedge (Micrasema bactro), and the Little Plain Brown Sedge (Lepidostoma roafi). The Net-winged Midges (Blepharoceridae) and some Chironomid larvae also graze on underwater algal carpets.

Aquatic insect larvae and nymphs which feed on decomposing leaves, conifer needles, woody materials, even animal tissue are called shredders or detrivores.

Detrivore eating mayflies include the Pale-morning Mayflies (Ephemerella spp), the Slate Winged Mahogany Mayfles (Paraleptophlebia spp), and some of the Epeorus species (eg E. nitidus). Most of the stonefly species found in a coastal streams, on the Pacific Coast of Canada, and many of the caddisfly species, are shredders or detrivores. In fact studies show that terrestrial detritus, deciduous leaves, and conifer needles account for up to 66% of the diet of the aquatic insects that are consumed by juvenile coho salmon.

In general, underwater shredders will be found in the slower flowing waters (eg pool and backwater habitat) where silt, leaves and decomposing debris has had time to settle to the stream bottom.

Aquatic insect nymphs and larvae which prowl stream bottom in search of larger prey to kill and eat are called predators. There are predacious stonefly larvae (eg Claasenia sabulosa, Hesperoperla pacifica, Isoperla sp, Diura knowltoni), predacious caddisfly larvae (eg Arctopsyche grandis, Dolophilodes pallidipes, Cheumatopsyche oxa oecetis inconspicua, Polycentropus spp, Rhyacophila spp), predacious chironomid (Chironomidae spp) larvae species and predacious Cranefly larvae (Tipulidae spp).

Underwater predators are the megalopteran species - the Alderf ly (Sialidae sp) , and the Fishfly (Corydalidae sp) . The Alderfly larvae grows to 18 mm, the Fishfly grows to 75 mm. They spend their time prowling though leaf packs, decaying vegetation, and spaces between rocks in search of any insect they can subdue with their large and powerful mandibles.

The Alderfly and Fishfly are rarely seen, but I do look for the distinctively clumsy flight of the emergent adults in the months of June, July and August.

Aquatic insects which eat both living plant and living animal matter are called omnivores. Most aquatic insect larvae and nymphs actively search for their food, some wait in ambush for the food to come to them, while a few (eg predacious caddisflies like Arc opsyche grandis, Dolophilodes pallidipes, Cheumato syche oxa, Oecetis inconspicua, and Polycentropus spp) construct elaborate spider-like silk nets to trap insects floating in the stream currents.

Undoubtedly there is much we do not know, when it comes to the how, what, when and where the various aquatic insects species divvy up the available food supplies.

As with the salmon and trout, there is a predictable, orderly sequence of emergence among the aquatic insects.

Early in the season, before the snow has even had time to melt from the valley bottoms, aquatic insects are already hatching from coastal river systems.

On warm days of February and early March I watch for the emergence of the little mayfly Baetis tricaudatus (Little Blue-wing Olive) , the caddisfly Psychoglypha alascensis (Snow Sedge) , the tiny Winter Black stoneflies (eg Capnia sp, Zapada cinctipes, and Despaxia augusta) , chironomids (eg Chironominae sp, orthocladiinae sp) , and black flies (eg Simulium sp) . The largest number of individuals and largest number of species of mayflies, stoneflies, caddisf lies, and true flies will emerge in the months of April, May, and June. During these months I particularly watch for the emergence of the Giant Stonefly (Pteronarcys californica), the Big Golden stonefly (Hesperoperla Pacifica) , the Great Grey Spotted Sedge (Arctopsyche grandis), the Summer Flier Sedges (Limnephilus sp), and the Fishfly (Corydalidae sp). Through the summer months I watch carefully for the emergence of the Giant Caddisfly (Dicosmoecus atripes), the Great Late-Summer Summer Sedge (Oncosmoecus spp) , and the Western Green Drake (Drunella spp) .

After July the number of different species which emerge declines rather drastically. By mid-September only a handful of mayfly, stonefly and caddisfly species are emerging. By November the only aquatic insects one will seeemerging will be Chironomid (Chironominae and Orthocladiinae) and a few blackfly species (simulium spp). The nymphs and pupae of each aquatic insect species also have their own methods of emergence. Some shed their nymphal skins or pupal cases while underwater and then float or swim to the surface.

Some do not crawl out of their nymphal skin or pupal case until they are at or near the water surface. Yet others crawl to shore or onto large rocks or logs sticking out of the water. Once out of the water they discard their nymphal or pupal skins and fly away.

In following articles I hope to introduce readers to details on many of these aquatic insects - where to find them, when they hatch, what they look like, as well as their importance to fish and the fly patterns which can be used to imitate them.