Bombus vestalis addicted to Giant Scabious

Bombus vestalis addicted to Giant Scabious

Observation - Bombus vestalis addicted to Giant Scabious. Description: The plant here is Giant Scabious, Cephalaria gigantea, and each year it seems attracts hordes of cuckoo bumblebees. Each time I've checked the bees they have been Bombus vestalis males. Other bumblebees also visit from time to time, but the male vestalis

The plant here is Giant Scabious, Cephalaria gigantea, and each year it seems attracts hordes of cuckoo bumblebees. Each time I've checked the bees they have been Bombus vestalis males. Other bumblebees also visit from time to time, but the male vestalis seem to become permanent residents on the flowers - there were over 30 of them at the time I took this picture. Why are they so addicted to this flower? Is it normal to have so many cuckoo bee males lounging about, or does this imply that local populations of bumblebees are suffering particularly badly from cuckoos?