A bumblebee, in common with most adult insects, has 3 pairs of legs.
On the bumblebees legs, especially the hind legs, there are a range of combs and brushes. The female bee uses these to gather the pollen that sticks to her hair and body together into one mass which she then stores in her pollen baskets.
Workers and queens have two pollen baskets, one each on the outside surface of each hind leg. The pollen basket is easy to spot; when it is empty it is a large, flat shiny area with spiky hairs around the edge, and when it is full it contains pollen which is often yellow, orange or red.
The leg above was taken from a dead terrestris queen. The pollen basket, or corbicula, is seen at an angle, so it is actually wider than shown.
Above is the outside of the rear leg of a worker/queen bumblebee. The claws, coxa, trochanter and femur are fairly unspecialised, and typical of those found in many insects. The outside of the tibia is concave, hairless and shiny when empty. It is bordered by a fringe of hairs, some of them are long and stiff. This forms the pollen basket or corbicula.
Pollen is pressed on to the the pollen basket when it has been collected by the combs and brushes on the inside of the legs (see the drawings and photograph below).
There are five segments to the tarsus. Segments 2, 3, and 4 are all similar. The last segment is usually a little longer than 2, 3, and 4. The first tarsal segment is large and flattened. It is called the metatarsus.
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 g and contain as much as 1,000,000 pollen grains. So for those of you who buy bee pollen to eat as a health supplement just think of the work that has gone into gathering it.
The bumblebee above and below has some orangey pollen in her basket. When the pollen baskets are full they bulge out and are quite easy to spot. This worker is foraging on bugle, but the pollen smeared all along her back in the photograph below comes from another, nuch larger flower. Perhaps a flower that does not supply nectar as she has her tongue out and is lapping up the bugle nectar. She certainly has worked hard, and perhaps needs a little more sugary energy to help er fly home with her heavy load to her mother and sisters.
When the queens first emerge in the spring 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. The bumblebee will moisten the pollen with some nectar to make it sticky and stay in the basket.
The photographs above show the pollen basket and pollen press of a queen and worker bumblebees, and that below a Bombus pratorum male. Note that the male has a hairy matte finish to his legs. Looking at the legs is often one of the easiest ways to tell the sex of a bumblebee.
Below you can see a magnified image of a bumblebee claw taken with a scanning electron microscope. The bumblebee claw is not very specialised and is typical of many insect claws.
In common with many other insects, e.g. beetles and ants, the bumblebee has a pair of antennae cleaners on each front leg, see the photograph below and the drawing above. The antenna is inserted into the notch (see above) then the metatarsus is bent enclosing the antenna. The antenna is then pulled through the notch and any debris or pollen is caught on the comb fringing the notch.