Caddisflies, order Trichoptera
Caddisflies are classified in the order Trichoptera. There are about 20 families in North America. Caddisflies are commonly called sedges, shadflies, sandflies, and the larvae are sometimes called caddisworms. Most caddisflies are intolerant of impairment, but common netspinners are tolerant of impairment.
The larvae of a few species are predatory, but most obtain food from algae, diatoms, plants, and animal materials that have settled to the streambed. Adults do not feed. Their only purpose is mating and egg laying.
Morphology and Behavior
Caddisfly larvae can grow up to ¾” to 1” in length. Common Netspinners are classified in the family Hydropsychidae. Other larvae that spin nets are Philopotamidae (fingernet caddisfly), and Polycentropodidae. The larvae build silk nets in swift water to snare food particle.
Case-making caddisflies take about a month to construct a small cylindrical shelter using their silk glands to bind together small stones or leaves from the streambed. Hydroptilidae caddisfly larvae make purse-like cases of silk, often with small stones attached. Limnephilid larvae build tubular cases from a variety of materials. Phryganeidae larvae construct tubular cases with plant fragments arranged in a spiral orientation. Rhyacophilids are free swimming. Brachycentridae are tube case-makers, and Glossosomatids make saddle cases out of sand and tiny rocks.
Caddisfly larvae live in their temporary homes for about two months and then emerge as a moth-like fly and swim to the water’s surface. They fly away to mate and lay their eggs back in the streambed. Some drop their eggs from their abdomen by rubbing it on the surface of the water in flight, while others lay eggs on plants above the surface. Some species dive to the bottom and deposit their eggs there.
Caddisflies usually have one generation per year, but small species could have 2 per year and large species could have one generation every other year. The period between the egg and larval stages takes about 10-12 days. The pupal stage generally lasts 2-3 weeks, and in this stage, the pupa generally swim to the surface. Adults generally emerge from April to November, but this can vary based on species. The adult lives for 2 weeks to 2 months and are nocturnal.
Many fishing flies are modeled after Caddisflies. In 1658, Mouffet, author of Theatrum Insectorum (the first English book on entomology), called Caddisflies “cados worms”. The name could have arisen from the term “cadice men”, a translation of an ancient name for traveling cloth salesmen. These salesmen pinned samples of their wares to their coats. The name Caddisfly could be a reference to this because the cases of many species are built from pieces of debris.
For more caddisfly pictures, click here
Research conducted by StreamWatch volunteer Ralph Hall