Oncopsis flavicollis can reach a length of about. It is a sexual dimorph species. Males show dark markings on the face with roundspots. Females are very variable, with different colour forms. Usually they are bright-yellow on the upper part of the face, on the forebody and on the base of the wings, while the remaining part of the wings are chestnut brown. Adult can be found in forestenvironment from May to September. These leafhoppers feeds on birch.