The youthful underwing (Catocala subnata) is a moth of the Erebidae family. It is found from Manitoba, Ontario, Quebec, and New Brunswick to Nova Scotia, south through Maine and Connecticut to North Carolina and west to Tennessee, Kentucky, and Texas, then north to Iowa, Wisconsin, and Michigan.
The wingspan is 75–90 mm. Adults are on wing from July to September depending on the location. There is probably one generation per year.
The larvae feed on Carya cordiformis, Juglans cinerea and Juglans nigra.