When at rest, they keep their wings folded one over the other. Microscopic examination is required to distinguish between species. The flies lay eggs in the soil surface near the germinating plants. Larvae feed on the developing seedling and, in the case of the onion maggot, on the expanding bulb. There are several generations per year.
Maggots prefer soils heavy in organic matter where they can survive and move to seeds.
Seed corn maggots occur throughout California garlic and onion production areas. Onion maggots are more restricted to cooler coastal climates. Maggots are primarily a pest of onions and do not generally cause economic damage to garlic. Their damage is usually restricted to the very early seedling stage. This results in increased rot in bulbs held in storage.