Catocala nymphagoga, the oak yellow underwing, is a moth of the Erebidae family. It is found in Southern Europe, from Bulgaria up to the Iberian Peninsula and sometimes further north as a migrant. It is also found in North Africa and Asia Minor. The wingspan is 35–43 millimetres (1.4–1.7 in). Adults are on wing from June to August depending on the location. The larvae feed on Quercus species.