The Bavius Blue occurs in small isolated populations on flower-rich, dry grassland, on dry, stony slopes and on open patches in shrub and in vineyards on calcareous soil. Various species of Salvia are used as foodplant, including Sage (Salvia officinalis), Salvia nutans, Salvia verbenaca and Whorled Clary (Salvia verticillata). Most important food plant in Romania is Salvia nutans as character species of steppic grasslands. The caterpillars feed mostly on the flowers, but sometimes also on the leaves. They are frequently found with ants. The Bavius Blue usually has one prolonged generation a year. In Peloponnesus, a partial second generation may occur. The pupa hibernates. In Eastern- and South-Eastern Europe there are many different endemic subspecies. In Transylvania the subspecies hungarica occurs, in South-East Romania it is the subspecies egea. In Peloponnesus the subspecies casimiri is found, while in Macedonia another subspecies macedonicus has been described. The habitat structure, ecology and biology was studied on populations of the subspecies hungarica in Transylvania. The largest of these populations has been monitored since 1977. In this period large natural population fluctuations have been recorded. The butterflies do not disperse easily; they hardly ever leave their breeding ground. Habitats: dry calcareous grasslands and steppes (50%), phrygana (20%), dry siliceous grasslands (10%), sclerophyllous scrub (10%), screes (10%).