The bee's knees

Inspired by Rusty Burlew's recent blog post on how honey bees fill their pollen baskets I have been taking a few photos to show the process in action.  The bee collects pollen grains on her body hairs and legs as she visits flowers.  I read that she also moistens the pollen grains with regurgitated nectar to make them more sticky.  By grooming with all six legs she moves the pollen onto the inside of the lower part of her back legs - the basitarsus.  These three photos show the two main parts of the bee's back leg below the "knee", the triangular tibia above and the rectangular basitarsus below.  These two segments are hinged at the front and the space between them and behind the joint is used to collect pollen into the pollen basket - the smooth lower part of the tibia, surrounded by a line of stiff curved hairs.

The inner surface of the basitarsus has horizontal ridges of stiff hairs which form a brush for collecting pollen.  It is about 2x1mm, so not the easiest part of a bee to photograph!

The space between the tibia and the basitarsus contains a row of hairs - the pollen rake - and the bee uses this to scrape the pollen grains off the basitarsus into the gap.  By straightening her leg the bee closes the pollen press and compresses the pollen which is squeezed up into the pollen basket on the outside of the tibia.

Here you can see the early stage of the formation of a pollen pellet in the pollen basket and see where the pollen has been squeezed up from below.

The bees on these Eryngium giganteum flowers were collecting nectar but not pollen.  Their pollen baskets contained different colours collected elsewhere.  This one has a small amount of grey pollen - possibly blackberry.

As pollen is collected the pollen pellet grows and is contained by the hairs around the pollen basket.

The tibia is concave to help retain the pollen. 

As more pollen is collected the pollen pellet expands upwards.  These photos also show that the hairs around the pollen basket become embedded in the pollen to help secure it.

The pollen remains firmly attached to the bee's legs until she gets back to the hive.  She removes it with her middle legs into a cell in the comb where it is packed by the house bees.  These last photos show the hairs around the pollen basket and the ridges of hairs on the inner surface of the basitarsus.