Pollen-storer. The colonies are in general established in dark, sheltered locations above the ground, in hollow trees, abandoned Swallow nests, and in bird boxes set in trees (Løken, 1973). Other nests sites include cavity walls (Hasselrot, 1962), woollen blankets (Sparre-Schneider, 1909) and in other locations within houses (Fuglår, 1963). The colonies are often larger than other species in the subgenus (80-400 offspring)(Bengtsson, 1903).
According to Rasmont (2008), most nests of Bombus hypnorum are located in tree holes, in abandoned bird's nests (Hasselrot 1960; Haas 1961, 1962, 1965). Wagner (1937) ascribes the expansion of this bumblebee species to the increasing habit of fixing man-made bird's nests in gardens.
In Great Britain, the species is a very common user of artificial nest boxes designed for birds, bats and dormice.
Bombus hypnorum queens are polyandrous and there are high levels of multiple mating (66%), with a mean of 1.7 males/queens (range 1-5)(Crowther et al., 2019)
B. hypnorum is unusual in that, because queens can mate with several males, between-worker relatedness within colonies is reduced. According to inclusive fitness (kin selection) theory, this facilitates the evolution of worker 'policing' (suppression) of workers' reproduction because it increases workers' relative relatedness to queen-produced males.