Development, location, and respiration of Compsilura concinnata (Meigen) (Diptera: Tachinidae) larvae were investigated using the silkworm, Bombyx mori (Linnaeus) (Lepidoptera: Saturniidae), as its host. C. concinnata was always found between the peritrophic membrane and the midgut of the host in the early larval stage. There they attached their posterior abdominal segment to or around the tracheoles of the host midgut using their anal hooks. C. concinnata at the later larval stage was found in the midgut cavity, where the peritrophic membrane had already been exuviated. The larvae actively took tracheae and tracheoles distributed on the coelomic surface of the host midgut into the midgut cavity.