Caddisfly larvae are nest-building aquatic insects found in streams and are also water quality indicator species

The caddisfly larva is not a silkworm, but the larva of the caddisfly, an insect of the order Trichoptera. It gets its name because it often lives among stones in streams and is good at spinning silk to build a nest. It spends most of its life in water, preferring to hide in the clear, well-oxygenated shallow areas of streams and rivers and in the gaps between gravel.

The caddisfly larva's most famous skill is nest building. The larva can secrete silk threads to glue sand grains, small stones, bits of twigs and fallen leaves into a small tube-shaped nest. It usually hides its soft body inside the nest, carries the nest on its back as it crawls, and retreats into it when in danger. Different species use different materials and build different nest shapes. When you turn over stones in a creek, you can often find these little creatures carrying their tiny houses.

From an ecological point of view, caddisfly larvae feed on algae, leaf litter and organic particles, take part in the decomposition and transformation of organic matter in the water, are an important link in the stream food chain, and are also natural food for many stream fish. They are very sensitive to water quality and can hardly survive once the water is polluted, so they are often used as indicator organisms for evaluating water quality and are highly valued in stream ecological surveys and environmental monitoring.

After the larva matures, it pupates inside the nest, and the adult that emerges is called a caddisfly. It looks like a small grayish-brown moth, is mostly active at night, and is attracted to light. For anglers, caddisfly larvae are a commonly used live bait in stream fishing; those who enjoy observing them can also keep them in an aquarium, but care should be taken to keep the water clean, cool and moderately flowing, and to lay down some sand and stones for them to build nests.