Bombus sylvarum, the shrill carder bee or knapweed carder-bee, is a species of bumblebee with a wide distribution across Europe, east to the Ural Mountains, and north to Great Britain, Ireland, and southern Scandinavia.
It is a small bumblebee; queens are 16mm18mm long and female workers are 10mm15mm. It is mostly pale yellowish in colour with a black band across the thorax, two black bands across the abdomen, and an orange tip to the abdomen. It flies rapidly and queens produce a high-pitched buzz.
The flight period lasts from about April to September. The queen bee emerges from hibernation in the spring. She makes a nest on or slightly below the surface of the ground among open vegetation. An old mouse or vole nest may be used. By summer, the nest may contain around 100 worker bees. Each nest requires about 10km2 of suitable habitat.
It occurs in herb-rich grassland where it feeds on nectar and pollen from a variety of flowers, especially ones that are complex or have long corollae. Important food plants include knapweed, woundwort, clover, vetch, red bartsia, and narrow-leaved bird's-foot trefoil.
It is threatened by habitat loss and intensification of agriculture and is declining in numbers across Europe. In the United Kingdom, it was common until the early 20th century, but is now restricted to a few small areas in southern England and south Wales. The species is included in the United Kingdom Biodiversity Action Plan. It is also an endangered species in Ireland.[1]