Queens fly from mid April (exceptionally late March) to the beginning of October, workers from mid June to mid October, and males from early July to mid October. On Madeira island, the species will fly throughout the year (Fellendorf et al., 1999)
Parasites and Predators: Bombus barbutellus may be a social parasite of this species (Westrich, 1989; Peeters, Raemakers & Smit, 1999).
Remarks: This species is very closely allied to B. hortorum, great care being necessary to distinguish between the two. The present species varies in the extent and brightness of the yellow body banding, this pilosity generally being rather sombre-coloured, although the bright yellow form is frequent. Total melanics (var. harrisellus (Kirby)) are also common and affect all three castes. This is not a geographical race as black specimens are frequently found alongside the typical yellow and black-banded form in the same nest. Some nests may only contain black individuals. This melanic variety is of interest as it appears to be restricted entirely to Britain.
Taxonomic status: B. argillaceus and B. ruderatus are similar in most characters and differ principally in the colour patterns of the queens (e.g. Reinig, 1939). Scholl, Obrecht & Zimmermann (1992) found that hybrid queens between B. argillaceus and B. ruderatus do occur in parts of southeastern France, but are very rare. Whether or not the taxa on either side of this hybrid zone are considered to be separate species therefore depends on which species concept is preferred. Because Scholl, Obrecht & Zimmermann (1992) estimated that only slight gene flow is occurring, I shall continue to treat them as separate species.
Introductions: This species has been introduced into New Zealand (e.g. Gurr, 1957; Macfarlane & Gurr, 1995) and Chile (Arretz & Macfarlane, 1982; Asperen de Boer, 1993b; Thorp, 2003)). B. ruderatus also occurs on the Azores (which have never had a continental connection), where it may be presumed to be an introduction (Yarrow, 1967).