In the UK there are 6 species of cuckoo bumblebees (3 illustrated). These were once like other bumblebees, but they have switched to a parasitic existence. The females kill or evict the queen and take over her workers as their own, using them to rear their own offspring. If you live in the south of England, males of the southern cuckoo bumblebee can be among the most common bumblebees in July and August.Cuckoo bees hang around outside the nest of the bees they are imitating in order to acquire their scent and make it easier for them to get in without a fight. Cuckoo bees only produce queens or males, hence their need to take over a nest and have the workers tend to their needs. However, if the host bee is rare then so is the cuckoo bee for that species. Cuckoo bees have no pollen baskets - they don't need them. They have fewer hairs on their legs, more chitin on their bodies and a longer sting. Cuckoo bees no longer have pollen baskets as they stopped collecting pollen a long time ago. Their legs are just very hairy. They also have darker wings.
MALE OR FEMALE BUMBLEBEE?
Female bumblebees have a concave area on their legs which is shiny and fringed with hairs (for carrying a big bag of pollen). Females have a pointed tip to the abdomen from which the sting emerges. They are literally busy bees, flitting around.
All photos and info courtesy of Bumblee Conservation Trust