Asked by: Steve McCabe, Skye
Bees, like all insects, have six sections to their legs: the coxa, trochanter, femur, tibia, metatarsus and tarsus. Each is connected by a joint and the one most like a knee is between the femur and tibia. Bees have lots of other specialised structures on their legs to carry pollen, but the bee's knee itself is no more remarkable than any of the other leg joints.
So with that in mind, what's the origin of the phrase: "the bee's knees"? Probably simply because "knees" rhymes with "bees".
The phrase seems to have evolved in 1920s America, along with "the cat's pyjamas". Other seemingly arbitrary terms of distinction from that era that have since died out include "the snake's hips", "the kipper's knickers" and "the sardine's whiskers". Of all of these, the only one actually found in nature is the bee's knees, so perhaps that's what's so special.