A single female moth is capable of depositing up to 1,000 eggs in her lifetime. The egg overwinters and begins to develop in early spring. Eggs hatch during April and May and the young larvae begin to feed on young, rapidly growing iris leaves. After feeding on leaf surfaces, causing scars from which sap runs down the leaf, the larvae assume a boring habit, entering the leaves and gradually mining downward. Leaf mining injury is characterized by dark, water-soaked areas or slits in the leaves.
Some chewing also occurs on leaf margins.
As the borers feed, bacteria infect the rhizome, initiating the soft rot. When fully grown, iris borer larvae are about 2 inches long, cylindrical, smooth, and plump with whitish to pinkish bodies and dark brown heads. Pupae are dark brown to black and are usually found in the top 2 inches of soil. After two to three weeks in the pupa stage, the iris borer moth emerges and the cycle is completed when the eggs are deposited. There is only one generation per year.