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 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.