Underwater architects

Caddisflies are common insects, in the order Trichoptera, which resemble moths as adults, but take on a considerably different form during their aquatic larval stage. In most regions caddisflies complete their life cycle in one year. Adults only live a couple of weeks, mate and deposit their eggs below the surface of rivers and streams. In a matter of weeks, the eggs hatch into larvae and they begin their architectural occupation. Most species of caddisfly larvae are case-makers that excrete silk from glands near their mouths, which is used to build a protective case out of sand, rock, twigs, and leaf pieces. Many people recognize them in this form, called periwinkles. Other species are net-making caddisflies that construct silk nets amongst aquatic vegetation, designed to capture food such as plankton and smaller aquatic insects. Much like butterflies, caddisflies pupate in a cocoon spun from silk, where over weeks or months they metamorphose into adults. Just before emergence (the “hatch”) the pupae become very active, and that is when they become extremely attractive to predators such as trout. Trout are not the only ones looking forward to the caddisfly hatch, anglers wait in anticipation, eager to take advantage of the trout feeding frenzy.