British Insects: Bumblebees and Cuckoo-bees
Subspecies perniger(Harris); Kirbys B. hortorum var. harrisellus, fidens misident.
Subgenus. Subgenus Megabombus.
Biology. Social insects forming organized communities; the larvae feeding on pollen and nectar gathered and prepared by the adult females.
Adult morphology. Adult queens, workers and males all similar appearance (but males usually of the paler form). Adults about 12–22 mm long (queens about 22 mm, workers 16 mm, males 15 mm). The hair coats of abdomen and thorax conspicuously colour-patterned (usually), or more or less homogeneously coloured or merely shaded darker to lighter; predominently when unpatterned, more or less all-black (melanism being fairly common, especially in males). Face relatively long; much longer than wide. The facial hairs of males black; vertex black haired. The facial hairs of females black; vertex black haired. The clypeus of females with scattered large to medium punctures over most of its surface, including much of the central area. The mandibles of males with a reddish beard. The mandibles of the females round-ended, not oblique. Thorax banded to not banded (blackish, often with mustard-yellow anterior and posterior bands, but these varying in intensity to dirty yellow or obscure); when banded, black across the middle, with pale anterior and posterior bands. The anterior yellow thoracic band narrower than the posterior one. The light thoracic hairs bright mustard yellow, or yellowish grey, or dirty yellowish, or pale greyish whitish. The outer surface of the hind tibiae of females with a conspicuous pollen basket, in the form of an elongate, shiny, hairless, area framed by stout hairs; pollen basket framed by black hairs. The hind tibiae of the males having a fringe of long hairs along the outer margin; with the long hairs on the hind edge falling short of the proximal end. Mid basitarsus of females with the distal-posterior margin extended to form a sharp angle of less than 45 degrees, or produced into a narrow tooth or spine. Scutellum of females at least partly pale-haired. Scutellum of males pale- or predominantly pale-haired.
The abdomen in dark forms of the females black with dark grey bands, in the lighter forms of the females, and the males, banded grey and black, sometimes the grey tinged with yellow or orange especially adjacent to the thorax. Abdomen fairly conspicuously patterned, or not conspicuously patterned (the females exhibiting pale forms, dark forms and intermediates, the males seemingly confined to light forms); with a contrasting tail, or without a contrasting tail (almost, in some dark forms?). The tail white to greyish white, or buff (usually white to greyish white, or grey to buff in dark forms). Abdomen conspicuously banded between the anterior of the tail and the thorax to without conspicuous banding between the anterior of the tail and the thorax; with a pale band adjacent to the thorax (this confined to the first tergite). Sternite 2 of females flat between the anterior and posterior margins. Sternite 6 of females without a median keel.
Male genitalia. The sagittae rather straight; externally finely serrate beneath the apex; apices narrow and straight, rounded and scarcely oblique. The ends of the claspers much expanded to somwhat expanded; dark and horny; conspicuously emarginate and toothed; with the volsella readily visible at their ends.
British representation. Recorded from England and Channel Isles. Rather scarce, confined to a few sites mainly in the English midlands and southern and south-eastern England. The adults abroad during April to September (females), or June to September (males). In flower-rich areas, especially fond of legumes and nettles.
General comments. The adult insects of the common B. hortorum are often not reliably separable morphologically from those of the scarce B. ruderatus, although genuinely all-black specimens (as distinct from merely dark ones with white tails) may all be referable to the latter..
Illustrations. • Male genital capsules of Bombus and Psithyrus.
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Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: Bumblebees and Cuckoobees. Version: 1st January 2012. http://delta-intkey.com’.