North America's streams, rivers, and lakes are home to more than 1,200 different species of caddisflies, which are aquatic insects in the order Trichoptera. Adaptations to different water conditions and food types allow this group of insects to populate a variety of habitats in America's waters.
Caddisflies are best known and most easily identified in their larval stages. Most caddisfly larvae either spin shelters of silk or build tubular cases. The type of shelter can be used to assign caddisflies to their different families. Some species make shelters from the hollow stems of grasses. Others inhabit shelters constructed from rock fragments, pieces of bark, or other available materials. Some species of caddisfly carry their shelters with them as they graze on the algae on rocks; others remain anchored to a rock. Caddisflies that spin silk shelters also spin nets that filter out food particles from the flowing water.
Immature caddisflies are aquatic and must obtain oxygen from the water. Mobile caddisfly larvae move water through their gills. Sedentary caddisfly larvae make undulating movements to move water across their gills. The larval cases of sedentary caddiflies restrict or direct flow in some essential way, for if the cases are removed, the larvae usually die.
Like many other insects, caddisflies undergo complete metamorphosis, from egg to larva to pupa to adult. The aquatic larvae eventually spin a cocoon or pupal case and become dormant. At the end of the pupation period, adult caddisflies break free of their cocoons and swim to the surface. There, the new adults dry their wings and begin their short adult lives as active, sexually mature air-breathing insects.
Most adult caddisflies live less than a month. During that time, they are inactive during the day, and active at night. Adult caddisflies feed on plant nectar, or other plant liquids. After the females have mated they lay their eggs. Where they lay their eggs depends on their species: One species of caddisfly remains underwater for more than 15 minutes as she lays her eggs. Another species deposits her eggs on plants above water, while another species lays her eggs on the water surface—the mass of eggs then absorbs water, sinks, and adheres to an underwater rock or other surface.
As an order, caddisflies are associated with a variety of aquatic habitats: rushing mountain streams, ephemeral spring seeps, slow moving rivers and tranquil lakes. A single habitat such as a stream, can support several different species of caddisflies as part of a complex aquatic food web. The larvae of a species grazes on algae on rocks, another feeds on leaves and other plant parts that fall into the water, shredding the material into fine particles. Another species filters food from the fast moving rapids, while another species catches of food items that flow by in slower-moving waters.
Caddisflies specialize in how they acquire food rather than in the type of food they ingest. These specializations make caddisflies one of the most varied and abundant species of aquatic insects in North America.