Within and Between-Leg Oil Transfer in an Oil Bee

Oil bees, which gather oil from flowers, transfer the floral oil collected from fore-legs, to middle-legs, and then to hind-legs, where they store the oil until release in the nest's brood cell. The complex leg maneuvers and the specialized hair types according to their location and function on the legs have been described in the past using morphological observations and in vivo behavioral monitoring, sometimes during flight. The aim of this work is to describe the different steps of oil transfer and to infer the role of the different hair types using a manipulative approach on isolated legs, controlled amounts of oil and high speed video recordings. A rapid and uni-directional capillary oil movement from the collecting ventral side of tarsi and/or tibiae to their dorsal side is observed in each fore-, middle-, and hind-legs. This suggests that plumose setae and pluridentate setae present different functionalities, acting either as oil donors or receptors, depending on their location on the legs. In the transfers observed, very little oil remains on the donor surface, so that a bee collecting oil from flower can quickly replenish the donor surface again.