Vestal

Vestal Cuckoo Bee (Bombus vestalis)

Clambering around amongst the many bumblebees currently gorging on pollen and nectar in the garden are a handful of these slightly larger visitors. They're also bumblebees, but they're bumblebees with a difference. This is the Vestal Cuckoo Bee (Bombus vestalis), called "cuckoo" because the queen doesn't start her own colony with her own daughters as workers. Rather, she dethrones the queen of an already-existing Buff-tailed Bumblebee colony (by killing her) and tricks the unsuspecting workers into providing for their now fraudulent queen and her offspring. Sneaky! Cuckoo bees are relatively easy to distinguish from their hosts, because they lack pollen baskets on their back legs. Their wings are often tinted a smoky grey (rather than being clear), though that can be a bit tougher to see. They also have a yellow band anterior to the white bands on their abdomen; true Buff-tailed Bumblebees have no such yellow band. Cuckoo bees have less "fur" on their thorax and abdomen than do other bumblebees, and have a thicker cuticle ("skin"), which helps the queens to resist worker stings when invading a hive. 

Mated queen Vestal Cuckoo Bees emerge from hibernation in late March or so, typically a few weeks later than their Buff-tailed Bumblebee hosts. (They have to give their host queens a chance to get their colonies started before emerging themselves.) They're active until August or so, when newly hatched queens emerge for a few days of mating flights before retreating to safe corners to hibernate for the winter. The males die when winter comes, as do all the workers who've laboured for the old queen for months. The species is common in grassland and gardens across England and Wales, but has only recently reached Scotland. They're also found across southern and central Europe, down into North Africa, and east as far as Iran. The Natural History Museum's website says males are "often abundant" in suburban gardens for much of the summer; they certainly are in ours!