British Insects: Bumblebees and Cuckoo-bees


L. Watson and M. J. Dallwitz

Psithyrus barbutellus (Kirby)

Field 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. hortorum, or B. hortorum and B. ruderatus.

Adult morphology. Adults about 15–20 mm long (females about 18 mm, males about 15 mm). Face at least as wide as long, or wider. The facial hairs of males black; vertex yellow haired. The facial hairs of females black; vertex yellow haired. The mandibles of the females obliquely-ended. Antennae of the male with the third segment at least as long as the fifth (the 5th only slightly the longer); with the third segment considerably longer than the fourth. Thorax banded (black, with a broad gingery-yellow anterior band and a greyish or (in males) gingery-yellow one posteriorly); black across the middle, with pale anterior and posterior bands; the light thoracic hairs yellowish grey, or 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 hind basitarsus narrower than the tibia.

The abdomen black, banded greyish adjoining the tail in the female, with a narrow yellowish anterior band in the male. Abdomen conspicuously patterned; with a contrasting tail. The tail white to greyish white. The white tail without yellow side patches. 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 exhibiting a thin line of yellowish hairs (sometimes interrupted) between the black ones and the white tail (male), or without a line of yellowish hairs between the black ones and the white tail (female). Sternite 6 of females without a reflexed spiny process at the tip; with 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 retuse, with a small bulge on each side near the tip.

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 visible tip more or less ovate, not incurving, internally finged).

British representation. Recorded from England, Wales, Mainland Scotland, and Ireland. Widespread in the British Isles, but most frequent over southeastern England and eastern coastal England and Scotland, seemingly now confined in Ireland to Sligo; seemingly less widespread than the host species. The adults abroad during April to September (females), or June to September (males).

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.’.