Niche differentiation of a cryptic bumblebee complex in the Western Isles of Scotland

1. It has recently become apparent that there is cryptic diversity in bumblebees, notably in the Bombus lucorum complex which appears to contain three distinct taxa (B. lucorum, B. magnus, and B. cryptarum). We know almost nothing about how these species differ in their ecology or distribution. 2. Here, we use RFLP markers to identify workers of the B. lucorum complex from the west of Scotland, and we map the distributions, forage use and habitat associations of the three taxa. 3. In western Scotland, B. cryptarum was found to be the most abundant of the three related taxa, but all three occurred in almost all sample sites. In combination with similar work from Ireland, we are able to conclude that: B. cryptarum is a polylectic species associated with uplands and cool climates; B. lucorum appears to be a lowland bee particularly associated with urban areas and islands close to the mainland in Scotland, and feeding largely on Erica cinerea and Apiaceae; B. magnus appears to be a heathland bee strongly associated with feeding on Calluna vulgaris. 4. Our study demonstrates that a combination of molecular and ecological approaches can reveal aspects of the ecology of cryptic species.