Photo by Ave Liivamägi (CC BY-SA 4.0)
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The Barbut's Cuckoo Bee belongs to the Bombini tribe; however, unlike most bumblebees, they don't live together in large social colonies.
This is because these bees are parasites. They've lost the ability to collect and forage pollen for themselves because instead, they steal from others!
A female cuckoo-bee will invade a bumblebee nest, and if undetected, she kills the queen and takes over. She then manipulates the colony to care for her and her own young.
Her young emerge, finding a new colony to invade. This large cuckoo bee targets the nests of Garden Bumblebees, and probably Ruderal Bee nests too.
Traits

Although these bees are parasites, they still play a key role in the surrounding ecosystem.

They will do some pollination when they first emerge from the nest!
Appearance
Adults: Females are around 1.5cm. They possess a dark-yellow collar, with some additional yellow hairs on the lower thorax and upper abdomen. They have white-tails, like their hosts- garden bumbles. The males appear similar, but they're smaller with more vivid colouration.
Tip: these bees lack pollen baskets, unlike garden bumblebees.
Larvae and Eggs: Gardeners rarely see these because they stay in the nest while they feed and grow!
Activity
Diurnal
Personality
Order
Hymenoptera
Family
Apidae
Metamorphosis
Complete
Distribution
These bees are present throughout Europe
Biological treatment
It's not suggested to treat gardens for bees. Help bees by planting pollinator-friendly flowers, provide bee-friendly habitats or cut down on the harmful chemicals used in the garden.
Chemical treatment
Bees are extremely sensitive to pesticides and herbicides. It's not advised to treat flowering plants or to spray near the latter because the bees can be affected even if they weren't intended to be.
Attracts
These bees tend not to forage too much, however, will feed on flower stores at the start of their lives so that they can begin egg production.