Bees actually have knees. The expression comes from the fact that they store large build ups of pollen in hairy baskets on their knees

Bees actually have knees. The expression comes from the fact that they store

The jointw between which must be considered to be 'knees'. ... They have hairs on their knees which are used to collect a big build-up of pollen. So, this could look like something very big and spectacular

The Bee Knee

A bee leg consists of six distinct segments, namely the Coax, Trochanter, Femur, Tibia, Basitarsus and Tarsi. ... These segments are connected with the help of joints; the one joint that most resembles a human's knee in terms of its location on the bee leg is the joint that connects the tibia and the 

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Pollen collection on 'scopa' or 'corbiculae' the hind legs

Some bees transport pollen on their hind legs. ... The bee thus becomes covered in pollen, and then uses its legs to wipe the pollen from its body down to stiff hairs on the abdomen or back legs.

When you refer to something as 'the bee's knees', it means that it is of excellent or very high quality. ... Some people believe that it is a reference to the fact that bees carry pollen in sacks on their knees, and that the expression therefore alludes to this concentrated goodness

A typical size honey bee colony (approximately 20,000 bees) collects about 57 kg of pollen per year. On average, 15-30% of a colony's foragers are collecting pollen. A single bee can bring back a pollen load that weighs about 35% of the bee's body weight.