British Insects: Bumblebees and Cuckoo-bees


L. Watson and M. J. Dallwitz

Psithyrus sylvestris Lepeletier

P. quadricolor misident.

Forest cuckoo bumblebee.

Biology. Solitary insects, parasitic on social bumblebees; the adult populations comprising males and fertile females only; the larvae parasitic in the nests of host Bombus species; hosted by B. jonellus, B. monticola, and B. pratorum.

Adult morphology. Adults about 13–16 mm long (females about 15 mm, males about 14 mm). Face at least as wide as long, or wider. The facial hairs of males black; vertex black haired. The facial hairs of females black; vertex black haired. The mandibles of the females obliquely-ended. Antennae of the male with the third segment at least as long as the fifth; with the third segment considerably longer than the fourth (the 4th being about 2/3 as long). Thorax banded (black, with a broad pale- or gingery-yellowish-brownish anterior band of hairs, and greyish hairs posteriorly); black posteriorly, with a pale anterior band only (usually), or black across the middle, with pale anterior and posterior bands (a posterior pale band commoner in males); the light thoracic hairs gingerish yellow, or orange-yellow, or pale greyish whitish. The outer surface of the hind tibiae of females with no ‘pollen basket’, strongly and uniformly convex, dull and uniformly covered with stout hairs. The hind tibiae of the males having a fringe of short hairs along the outer margin.

The abdomen in females black with a narrow pale band anterior to the white tail; in males more slender, black anteriorly, with a broad yellowish-gingery band before a narrow dark one which precedes the white tip of the tail. Abdomen fairly conspicuously patterned; with a contrasting tail. The tail white (in female), or white and orange (in males). The white tail black at the extreme tip, or with some orange hairs at the extreme tip (only in males). Abdomen conspicuously banded between the anterior of the tail and the thorax, or without conspicuous banding between the anterior of the tail and the thorax. Abdomen without a line of yellowish hairs between the black ones and the white tail. Sternite 6 of females armed at its extreme apex with a reflexed, angular spine or tooth (this representing the curved-under tip of the abdomen); without a median keel; with ventro-lateral keels; with only small anterior callosities, one on each ventro-lateral keel; the callosities separate, not coalescing and not visible from above. Sternite 6 of males without black hair-tufts.

Male genitalia. The sagittae rather straight; with a small hook externally around the middle or somewhat above; apices apically turned outwards, obliquely truncate and minutely hooked externally at the tip, or apically turned slightly outwards and obliquely truncate, not hooked. The ends of the claspers much expanded to somwhat expanded; pale and soft; conspicuously emarginate and toothed; with the volsella readily visible at their ends (the tip narrowly elongate, not fringed).

British representation. Recorded from England, Wales, and Mainland Scotland. Widely distributed in Britain, though local. The adults abroad during April to September (females), or May to September (males). In divers habitats, cf. the host species.

Illustrations. • Psithyrus rupestris, P. vestalis, P. campestris, P. sylvestris, P. barbutellus: Saunders. • Male genital capsules of Bombus and Psithyrus.

To view illustrations with legends giving names in current use, go to the interactive key. This also offers full and partial descriptions, diagnostic descriptions, differences and similarities between taxa, lists of taxa exhibiting or lacking specified attributes, and distributions of character states within any set of taxa, as well as source references and other relevant material.

Cite this publication as: ‘Watson, L., and Dallwitz, M.J. 2003 onwards. British insects: Bumblebees and Cuckoobees. Version: 1st January 2012.’.