Due to their tolerance of cold temperatures, bumblebees can still be found foraging on late-blooming flowers such as New England Asters (Symphyotrichum novae-angliae). Most worker bees collect and carry pollen in a dense mass of elongated and often branched hairs (setae) on their hind legs called a scopa. Honeybees and bumblebees, however, have pollen baskets, or corbiculae, in which they place and carry pollen back to their hive. Pollen baskets consist of a polished cavity located on the tibia of each of their hind legs which is surrounded by a fringe of hairs. Pollen is pressed on to the pollen basket when it has been collected by the combs and brushes on the inside of the bee’s legs. The bumblebee moistens the pollen with some nectar to make it sticky and stay in the basket. The pollen is loaded at the bottom of the pollen basket, so the pollen that has been pushed towards the top is from flowers the bumblebee visited earliest on her foraging trip. When a pollen basket is full it can weigh as much as 0.01 gram and contain as much as 1,000,000 pollen grains.
Only queen bumblebees overwinter, and they must start a new colony in the spring. When the queen first emerges you can tell whether or not she has started a nest by looking at her pollen baskets. If she is carrying pollen then she has found a nest site.