Dehesas are typical Mediterranean habitats for extensive livestock raising. Hoverflies (Diptera: Syrphidae) may act as bioindicators in dehesas, but they are still poorly known in this habitat type. With the purpose of the present study, hoverfly diversity was surveyed in Campanarios de Azaba, a typical oak dehesa in Salamanca province, Spain. A total of 41 species were recorded, including Eumerus azabense sp. nov. This new species was found to belong to the Eumerus tricolor group, both in morphological and genetic terms, and clearly separated (DNA characters) from the similar Eumerus niveitibia, which is redescribed here. Genetic monophyly of the E. tricolor group is confirmed in the present paper. An updated hoverfly checklist of Salamanca province is provided (152 sp.) with indication of the 56 species recorded in Campanarios de Azaba. Obtained results address the importance of dehesa biodiversity, which includes species new to science.