All bees have an antenna cleaner on each of their two forelegs. The antenna cleaners are made of two parts: a notch in the basitarsus, which is fitted with stiff hairs, and a corresponding spur on the tibia. According to Mattingly (2013) “To use the antenna cleaner, the [bee] raises her foreleg over her antenna and then flexes her tarsus. This action allows the spur to close the notch and form a ring around the antenna.”
Antennae have many functions
The bee pulls each antenna through the bristles to clean it of debris such as pollen or dust which might interfere with the many sensory organs within the antenna. According to Caron and Connor (2013) “Antennae smell, taste, perceive humidity and temperature, feel, monitor gravity and flight speed and even detect sound waves to help guide the bee in her daily activities.” Considering their importance, you can see why bees have to keep their antennae spit-shined and polished.
The little bee in the photo is a male Halictus rubicundus. I watched him sip nectar and then raise up on his hind legs and pull each antenna through the cleaners several times before flying off to the next flower. He repeated this pre-flight ritual between every blossom. These bees have long antennae, so it was easy to see even though the bee is quite small.