A young larva is only a few millimetres long. Over six to nine months the larva grows steadily until it is about 3–4 centimetres long. It hangs loosely from a damp, sheltered surface, inside a horizontal tube made of very flexible silk and mucus. When mature the larva becomes a pupa. In the pupal or cocoon stage the pupa hangs vertically from a thread for about two weeks until emerging as an adult fly. The adult fly cannot feed and lives only a few days – enough time to mate, and for the female to lay about 100 eggs.