Ontherus sulcator (Fabricius) is a species of Dichotomiini sensu lato, which usually constructs paracoprid nests composed only one brood ball per nesting chamber, conforming to Nesting Pattern II. The typical brood ball is spherical with a thin wall and a cylindrical, flattened T-shaped protrusion at the egg chamber pole. This study revealed that females of O. sulcator are capable of showing activational behavioral plasticity when, instead of constructing their stereotyped brood balls, they elaborate simpler brood balls, and even more, cylindrical brood masses. This is the first recorded case of a dung beetle having the ability to change its nesting behavior in experimental conditions, from constructing brood balls (Nesting Pattern II) to constructing brood masses (Nesting Pattern I). Cylindrical brood masses are also constructed by species of some other genera within Dichotomiini sensu lato, which were proposed as phylogenetically more closely related to Ontherus. The capability of construction of these brood masses in O. sulcator, shown by activational plasticity, supports these proposed relationships.