Common Netspinners


Common netspinners are classified in the order Trichoptera and in the family Hydropsychidae. Netspinning caddisfly larvae are fairly tolerant of habitat and water quality impairment.


The larvae live in flowing water where they build silk mesh nets on or between rocks, submerged logs or other debris. Both the pupal and egg stages are also submerged in water. Adult netspinners usually live near water.


Netspinner larvae are omnivorous. The larvae spin an underwater net, which collects food particles as water flows through it. Food collected includes algae, diatoms, crustaceans and immature aquatic insects. The larva comes out of its retreat to eat food collected on the net. During the adult stage, netspinner adults have reduced mouthparts and can only suck fluids such as nectar.


Caddisfly larvae average 13 to 18 mm in length, and are often greenish in color. Larvae have gills on the underside of their abdomens. Each thoracic segment is covered with a hardened plate. On each thoracic segment, there is a pair of jointed legs with a claw on each leg, and the abdomen ends with a brush of hairs. Larvae have modified salivary glands from which they spin silk. Adult netspinners are moth-like with long, many-segmented antennae and two pair of membranous, hairy wings that are held roof-like over body.

Netspinners secrete silk similar to that spun by butterfly and moth caterpillars. In fact, they, like other caddisflies, are closely related to the order Lepidoptera. Netspinners are a major food for fish, especially during their emergence from the pupal stage and during the return of adult females to the water to lay eggs. Netspinners are very territorial, defending their territory first by stridulation (making noise by rubbing their front legs against side of head) and then by fighting using mouthparts and anal claws.


Netspinners go through a complete metamorphosis that usually takes one year. The eggs are laid in water in gelatinous masses. They are attached to rocks and hatch about a month later. The larvae are caterpillar-like and can remain in this stage for one to two years. The larval stage usually has five instars (growth stages separated by molting) before pupating. The pupa is encased in a cocoon of silk and sand or small pebbles submerged under water. The pupal stage lasts 2 to 3 weeks after which pupa uses its mandibles to cut through the cocoon and then swims to the surface. Pupae often drift along in the current while emerging. Emergence from the pupal stage in this area takes place from May through September. The adult netspinner is moth-like, and lives during the summer for about one month. Adult netspinning caddisflies mate while swarming in the evening. Females crawl or dive into water to lay eggs.


  2. Voshell Jr., J. Reese. 2002. Blacksburg, VA: McDonald Woodward Publishing Company. A Guide to Common Freshwater Invertebrates of North America.

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Research conducted by StreamWatch volunteer Tana Herndon