What material do female European Wool Carder Bees use to construct their individual nest cells?

Answer

Soft, often silvery or grayish, plant hairs

Unlike honeybees or bumblebees that use wax, the female actively harvests fine plant fibers or fluff to construct and insulate the small, thimble-sized brood cells.

What material do female European Wool Carder Bees use to construct their individual nest cells?
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