A Study of the Hibernation of Bumblebees (Hymenoptera:Bombidae) in Southern England

In temperate parts of the world such as the British Isles, bumblebee colonies are annual, since only the young queens are able to survive the winter, while the old queens, workers and males all die. The young, fertilized queens produced during the summer months enter hibernation, and it is these bumblebees which reappear in the following spring and later form colonies of their own. In southern England the period of hibernation may last anything from 6 to 9 months, depending on the species and to some extent on spring temperatures. Hibernation is, therefore, an important yet neglected aspect of bumblebee biology. Previous workers (Sladen 1912; Bols 1937, 1939) have indicated that well-drained banks or slopes with a north or north-west exposure are favourite sites for hibernating bumblebees, and both Wagner (1907) and Sladen (1912) have stated that bumblebees hibernate under trees, but do not give precise details. Bumblebees have also been recorded hibernating in rotten tree stumps (Frison 1926; Tkalcu 1960, 1961), under moss, leaves and piles or rubbish (Verrill, in Putnam 1864; Sladen 1912; and others), and in various other miscellaneous places. Plath (1927, 1934), Frison (1929) and Townsend (1951) have all reported the occurrence of many queens of the New World species Bombus impatiens (Cresson) hibernating in very close proximity to one another, and presumably in all these cases the queens were hibernating about the entrance to their maternal nest. However, much of the information on the hibernation of bumblebees so far published has accumulated from casual observations which have not been followed up by more critical data, and apparently only Sladen has investigated the subject of the natural hibernation of bumblebees in this country. In the present studies an attempt has been made to obtain data on various aspects of the natural hibernation of bumblebees and where possible differences between species or groups of species have been investigated.