Male phenology ofbumblebees (Hymenoptera: Apidae: Bombus) in southern Switzerland. -The paper presents the phenology of 4185 individuals of 7 bumblebee species (Bombus honorum, B. hypnorum, B. lapidarius, B. lucorum, B. pasciiorum, B. pratorum, B. terrestris) sampled weekly using Kombi traps (from 17.3 to 30.9.1997) in Ticino in former coppice stands of sweet chestnut (beside Lago Maggiore, Southern Switzerland). All the species showed an extraordinarily high flying activity in March due probably to the warm winter of 1996/97, which was considerably warmer than those during the last 30 years (1966-96). Males of B. pratorum and B. terrestris started to fly unusually early in spring 1997, 25 March and 8 April respectively. The highest number of males in B. honorum, B. hypnorum and B. pratorum per week were observed already in May. Moreover, males (at least as a caste) flew for a longer period of time than in the better studied situation in Central Europe. B. honorum clearly showed a bivoltine cycle, but B. pratorum did not. Nevertheless, it seems likely that a few males of the latter species and also of B. terrestris could have overwintered. Early flying males alternatively could also have originated from overwintering virgin queens. Are entire colonies sometimes able to overwinter or even to fly in this season? This would be worth further research, particularly on B. terrestris and B. pascuorum.