Adult Caddisfly and Caddisfly Larva (Casemaker) - Order Trichoptera
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Some species of caddisfly larvae use their own glue to assemble sand grains, bits of shell and even plant
fragments into a tube in which they hide.

Very common "little black caddis" in the genus Chimarra. Science Lake, Allegany State Park, New York.
Caddisfly adults resemble moths, but the wings are covered with fine hair instead of scales. (Trichoptera = "hair wing.") Caddisfly larvae are a favorite food of many fish, including trout, and are used as bait by sport fishermen. The larvae are especially sensitive to water pollution and their numbers can be monitored over a period of time as a good indicator of water quality.

These primitive flying insects are most abundant near well-aerated streams and fast-flowing water, but also frequent lakes, ponds and marshes. This specimen was found at the west branch of the DuPage River, a fairly sluggish body of water, home to both large and smallmouth bass, walleye, and panfish such as bluegills and sunfish.

Adult Caddisfly
Adult caddisfly holds its wings roof-like over its body at rest.
well-camouflaged caddisfly
Adults are well-camouflaged in many situations
Adult caddisflies are commonly called sedges. Caddisflies (and mayflies) frquently hatch en masse, providing swarms of flying insects that attract sport fish, especially trout. Fishermen take advantage of these hatches by fly-casting both wet and dry flies mimicking these insects.

Casemaker
Photo: Government of New South Wales, Australia

Caddisflies undergo complete (holometabolous) development. After hatching from an egg, the lava will progress through five instars (building a new, larger case at each stage), then pupate inside the last case before emerging as a winged adult. The larva has six legs arranged in three pairs near the head, and small hooks near the tail which it uses to anchor itself inside the case.

Most species have gills and get their oxygen from the water that circulates through the case; this may explain their sensitivity to water pollution which affects the level of dissolved oxygen in their environment. All development before the adult stage takes place in water; some species' larvae are predatory and spin silken structures underwater to trap prey. The predatory species are free-swimming and do not build cases.

Case construction is distinctive for each family or genus of caddisfly.   The case is portable, dragged around like a snail shell as the larva moves, and held in place by a pair of hooked prolegs at the tip of the abdomen.

Casemaker
Caddisfly larva with case made from plant stems
Photo: Government of New South Wales, Australia
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Moths and their larvae (caterpillars) are major agricultural pests worldwide. The caterpillar of the gypsy moth (Lymantria dispar) causes severe damage to forests in the northeast United States, where it is an invasive species. In tropical and subtropical climates, the diamondback moth (Plutella xylostella) is perhaps the most serious pest of brassicaceous crops.
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