Invertebrate Zoology: A Study Guide - T. A. Dauda 2014

Multicellular Animals
Arthropods
Subphylum Tracheata - Class Insecta - Orders with Complete Metamorphosis - Order Trichoptera

This order comprises over 3,000 species. Adult caddisflies are small, moth-like winged insects of brownish or greyish coloration (Fig. 74). Their wings resemble those of butterflies and are covered in Hair-like scales. The mouthparts of the imago are poorly developed and adapted solely for licking up liquid food, while some forms do not feed at all. Adult caddisflies are found near Water bodies. Typically, they rest on vegetation with their wings folded tent-wise over the body, and are weak flyers. Some can land on water and run across its surface. Females deposit their eggs directly into the water, hatching into caterpillar-like larvae. In some species, the larvae are predatory and do not construct cases.

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Fig. 74 Caddisflies:

1 — adult form; 2 — larva.

Most larvae construct protective portable cases of various shapes around their bodies. The building Materials include pine needles, fragments of aquatic plant leaves, sand grains, and empty shells of small dead Mollusks. These materials are bound together by the silk secretions of specialized spinning glands. The cases blend in seamlessly with underwater objects or mimic pieces of plant debris.

The larvae possess chewing mouthparts and feed predominantly on plant matter. At the tip of the abdomen, they feature paired appendages with hooks that help the larva anchor itself securely inside its case. At its tapering posterior end, the case has an opening through which water is pumped inside by abdominal undulations to irrigate the gills. Before pupation, the larva seals the opening of the case and subsequently transforms into a pupa.

Pupates feature well-developed mandibles. In mid-summer, they chew through the case lid and, using their swimming hind legs, paddle in the water for a few minutes before crawling up onto aquatic plants, where the final molt takes place, giving rise to the adult imago.

Caddisfly larvae constitute a substantial portion of the fish diet. Their population growth is particularly significant in commercial pond fisheries.