Differences in the forelegs of bees are often a secondary sexual characteristic that affects male bees and plays a role in their chances of finding a mate.
Forelegs can be used to cover the females eyes as they mate. The different shapes and sizes of the forelegs between species cause different shadows and patterns of light to shine through as he covers her eyes. These patterns signal to the female bee that she is mating with her own species.
Forelegs are also used to collect scent, whether the scent is excreted as a pheromone (such as can happen in Leaf-cutter bees) or collected from a series of flowers (such as in Orchid bees). This scent is then used as a signal to attract a mate and to assure her that they are the same species. When secreting pheromones, the scent can also be used to distinguish the relationship between the female and her mate, to assure that they are not closely related. The forelegs can also come equipped with dense, soft hair to massage the sent into her antennae.
The forelegs can also be modified to collect oil from flowers in addition to pollen, though this is not a male-specific trait. The oils are collected using a dense brush of hairs on the front of the leg.
This information is also available from the University of Calgary Invertebrate collection, where it was curated as part of a study on design inspired by bees.Edit Summary
“The forelegs of male leaf-cutter bees reveal mysterious structures: one of the tarsi is extremely enlarged and has a scoop-like protuberance. While evaluating the video recordings Professor Wittmann and his team discovered that shortly before copulation the female’s feelers are placed in the curved blade of the scoop. In the examination by electron microscope they also discovered that the scoop blade is pockmarked with tiny holes, the outlets of scent glands. The curved scoop-like shape serves the male as a ‘hand spray’, with which he sprays the feelers of his partner (her nose) with his sexual scent. At the same time the male bee places his forelegs, which in part are translucent, over his partner’s eyes, thereby creating a species-specific pattern of light and shadow.” Wittmann, 2002