One of our smaller cuckoo bumblebees, a parasite of B. pascuorum and possibly other carder bees such as humilis and ruderarius. It is a rather variable species which can produce challenges during field identification. Females are relatively small, fluffy and with a sparse body pilosity, especially on the abdomen. The typical pattern comprises a broad buff collar, a conspicuous buff-haired scutellum and a tail that is buff-haired at the sides but remains black-haired in the middle. Darkened females are occasionally encountered, whilst in Scotland, females are occasionally found with the thorax almost entirely yellow (form swynnertoni).
Males are extremely variable. At the palest extreme they are almost entirely pale-haired except for a black band between and below the wing bases and another black band around tergite 2. The thorax frequently becomes entirely black leaving just the tip of the abdomen buff-haired, and fully black individuals are not rare. It is also possible to find males with white tails which can rather resemble barbutellus males, though the white tail is generally more extensive in campestris (tergite 3 onwards). Fortunately, campestris males have a conspicuous pair of hair tuft on sternite 6 which should be viewable on a hand-held specimen using a hand lens, and the genitalia is very distinct (checking this will necessitate the taking of a specimen)… Steve Falk