Abstract
From June to September, 2003, we searched rural areas (7.75km^2) in Mukawa, Atsuma, and Monbetsu, in the Hidaka region of southern Hokkaido, for natural nests of alien (Bombus terrestris L.) and native Japanese bumblebee species. Twentyseven nests were found. Eight B. terrestris nests had been made in abandoned rodent nests underground. The number of individuals (i.e., eggs, larvae, cocoons, adults), and nest characteristics, such as food storage and the number of excretions, were recorded for nine of the 27 nests. The B. terrestris colonies contained a mean of 110 new queens; this mean is 4.4 times larger than the mean for native bumblebees. This strongly suggests that the reproductive ability of B. terrestris is higher than that of the native bumblebees in the region.
