The caddisfly is an aquatic insects that resembles small moth. Silk is produced by the larvae through a pair of labial silk glands. The larvae, caddisworms, use silk not only to produce ‘capture nets’ to collect food particles from the water environment but also to construct ‘silken cases’ for their shelters in running water. Physically, two different processes of silk-producing systems are reported among the different species of arthropod animals: terrestrial and aquatic silk productions. Although both types of silks can be produced along its sophisticated process through a sequential pathway from silk gland, most of our recent knowledges of silk producing system are dependent on those revealed from the terrestrial animals including silkworms or spiders. Therefore, this experiment was initiated to reveal the fine structural aspects of the silk producing system of larval stage of the caddisfly Hydatophylax nigrovittatusu with light and electron microscopes