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 on the left was taken from a dead terrestris queen. The pollen basket, or corbicula, is
seen at an angle, so it is actually wider than shown.
Parts of the bumblebee leg
Below 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.
Loading pollen into the pollen basket
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.
Differences between male and female hind legs
The photograph on the right shows the pollen basket and pollen press of a Bombus terrestris queen, and that on the left 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.
The bumblebee on the left has some orangey-brown pollen in her
basket. When the pollen baskets are full they bulge out and are quite easy to
The bumblebee on the right was resting to get up heat. Her pollen baskets are well
filled with light yellow coloured pollen.
When the queens first emerge in the
spring you can tell whether or not a queen 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.
On the right 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 on the left and the drawing on the right. The antenna is inserted into the notch (see right) 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.