Leek moth has two generations during the summer with larvae feeding on the plants in May to June and August to October. The second generation is the more numerous. Initially the caterpillars mine the foliage but the older larvae bore into the stems and bulbs.
When fully fed, the caterpillars are 11 mm long. They exit the plant and pupate within net-like silk cocoons that are spun on the foliage. Adult moths emerge in autumn and overwinter in sheltered places.