Leo Pardi (1915–1990) was the initiator of ethological research in Italy. During more than 50 years of active scientific career, he gave groundbreaking contributions to the understanding of social life in insects, especially in Polistes wasps, an important model organism in sociobiology. In the 1940s, Pardi showed that Polistes societies are organized in a linear social hierarchy that relies on reproductive dominance and on the physiological and developmental mechanisms that regulate it, i.e. on the status of ovarian development of single wasps. Pardi’s work set the stage for further research on the regulatory mechanisms governing social life in primitively eusocial organisms both in wasps and in other insect species. This article reconstructs Pardi’s investigative pathway between 1937 and 1952 in the context of European ethology and American animal sociology. This reconstruction focuses on the development of Pardi’s physiological approach and presents a new perspective on the interacting development of these two fields at the origins of our current understanding of animal social behavior.