Differences in the hind legs of bees are often a secondary sexual characteristic, affecting male bees and increasing their chances of finding a mate.
The legs are often used to hold onto the female during mating. Many species mate in midair, so the ability to stay coupled is important. Hind legs are often expanded, widened or modified with spines. The inner surface of the hind legs may also be contoured to fit perfectly against the female, varying from species to species.
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
“Upon contacting a female, a male rapidly climbed on her, and wrapped his hind legs around the latero-ventral portion of metasomal sterna 1-3 (C and B: “His hind legs lock beneath the posterior portion of her abdomen’). The hind tibiae are greatly expanded, and the inner faces are contoured to fit the general shape of the female metasoma.” Wcislo et al. 1992:433