British Insects: Bumblebees and Cuckoo-bees


L. Watson and M. J. Dallwitz

Psithyrus vestalis (Geoffroy in Fourcroy)

Southern 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. terrestris.

Adult morphology. Adults about 15–22 mm long (females about 21 mm, males about 16 mm). Face at least as wide as long, or wider. The facial hairs of males black (with a few yellow hairs on the vertex); vertex with some yellow hairs among the black ones. The facial hairs of females black; vertex black haired. The mandibles of the females obliquely-ended. Antennae of the male with the third segment shorter than the fifth (the 5th almost as long as the 3rd and 4th together); with the third segment considerably longer than the fourth. Thorax banded (black, with a broad gingery-yellow anterior band and greyish posteriorly); black posteriorly, with a pale anterior band only; the light thoracic hairs gingerish yellow, or orange-yellow. 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 hind basitarsus as wide as the tibia.

The abdomen black, with a thin (sometimes interrupted) yellow or gingerish band before the tail. Abdomen conspicuously patterned; with a contrasting tail. The tail white (with yellow side patches). The white tail with yellow side patches anteriorly. Abdomen conspicuously banded between the anterior of the tail and the thorax (in some males), or without conspicuous banding between the anterior of the tail and the thorax (mostly). Abdomen exhibiting a thin line of yellowish hairs (sometimes interrupted) between the black ones and the white tail. Sternite 6 of females without a reflexed spiny process at the tip; without a median keel; with ventro-lateral keels; with large, conspicuous, bulging callosities associated with the ventro-lateral keels; the callosities separate, not coalescing and not visible from above. Sternite 6 of males without black hair-tufts; posteriorly rounded, without bulges near the tip.

Male genitalia. The sagittae rather straight to curved inwards around the spatha; smooth to the base, neither serrate nor dentate nor hooked externally; 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; pale and soft; conspicuously emarginate and toothed; with the volsella readily visible at their ends (the tip broad and incurving, internally fringed).

British representation. Recorded from England, Wales, Mainland Scotland, and Channel Isles. Widespread in England and Wales north to southern Scotland, lacking from Scotland and Ireland, discounting an early record for Co. Wexford. The adults abroad during April to September (females), or June to September (males). In divers habitats (cf. the host).

Illustrations. • P. vestalis: female and male (photo). • 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.’.