Bombus (Alpinobombus) hyperboreus
Bombus hyperboreus is uncommon in the collections and mentioned in few writings. The species lives beyond the tree-line and on the alpine stage of the Scandinavian mountains, at latitudes nowhere lower than 60° N. Its distribution is more strictly Arctic than for B. polaris and in N. America, it is absent from the shores of the Hudson Bay, as from Quebec and Labrador, but reaches the far north of Ellesmere Isl. and Greenland, well beyond the 80th parallel.
In the West-Palaearctic region, the range of B. hyperboreus is the same as that of B. polaris, including Novaia Zemlia, Wrangel and some other islands of northern Russia and Siberia. However, it is always less common than the latter species.
The inquiline behaviour of hyperboreus is quite remarkable : this is the only bumblebee species, out of the Psithyrus, for which inquilinism is a well documented practice. In N-Canada, Greenland and Novaia Zemlia, B. hyperboreus appears as a workerless obligate parasite (K.W. Richards 1973, Löken 1973). In Norway and in Wrangel island, some queens of this species are able to forage and to produce some workers, even if most queens act as inquilines (Löken 1973, Berezin 1994).