Queens fly from late March or April to October, workers from mid May to late September or early October, and males from late June (exceptionally mid May) or July to the end of September. Some British populations may be double-brooded, as freshly-emerged males, for example, have been encountered both in mid May and in early September. Yalden (1983b) has also speculated on the possibility of a second brood in England.
In Spain, the flight period is from June to the end of August (Ornosa & Ortiz-Sánchez, 2004).
Parasites Possibly Bombus sylvestris is a social parasite of this species (Richards, 1928; Yarrow in Free & Butler, 1959; G.M.Spooner, pers. comm.), but confirmation is desirable. Westrich (1989) cites Bombus flavidus as a social parasite of this species.
Systematics : This species was formerly known by the name B. lapponicus (Fabricius, 1793) in the British literature. However, Svensson (1979, 1980) showed that in western Europe this taxon consisted of two very closely related species, B. lapponicus sensu stricto and B. monticola (Smith, 1849). It is only the latter which occurs in the British Isles. The true B. lapponicus is a Holarctic species, in the western Palaearctic confined to Fennoscandia (excluding southern Sweden and southern Finland). Svensson's illustrated paper provides characters to distiguish B. monticola from B. lapponicus.
Conservation: There has been a considerable decline in the distribution of B. monticola in England in recent years (it is on the English Nature Species Recovery Programme) and there is some evidence that its range has also decreased in Scotland. This may be due, at least in part, to a decrease in suitable habitat and quality of that habitat. The procedure of regular, periodic burning of small areas of grouse moor (muirburn) to provide new shoots of heather for young grouse probably also benefits B. monticola by increasing the diversity of flowering plants. In particular, Blaeberry, Cowberry and Bell Heather often become dominant in the early years after burning. A decline in the active management of grouse moors in recent years may have contributed to the decline of this species.