Caddis Flies are an order of insects known as the Trichoptera; they mainly belong to one family, the Phryganidae. The main features of the order are these: the metamorphosis is incomplete, but the pupa is active for part of its life; the masticatory organs around the mouth are mainly rudimentary in the adult but not in the pupa or chrysalid stage; and there are four wings which are all equal or nearly so; the hinder pair may be hairy or folded. One of the best known characters of the group is that the larva lives in a tube composed of fragments of stick, shells, and sand; these tubes float about on the surface of ponds and streams. The "indusial" limestone of Central France is said to be composed of these cases (indusia) of Caddis flics. Phryganea grandis is the commonest English species; the adult is a brown insect measuring two inches across the wings.