Melitta differs from the other Melittidae s.str. by several plesiomorphic features. The males are characterized by the structure of S7 with a large disc and by lateral processes weakly developed. This conformation is similar to the structure observed in Apoidea Spheciformes (Michener 1981). Melitta species also share a few additional apomorphies, like lateral tubercles on the labrum, apical projection on the posterior basitarsus and volsella with elongated digitis (Michener 1981).
The cladistic analyses of Michez & Eardley (in press) supported the monophyly of the genus Melitta. Moreover, two subgenera have been defined: the subgenus Melitta Kirby s.str. (7 species) and the subgenus Cilissa Leach (36 species).
At the species level, the Melitta are unambiguously characterized by a combination of a few morphological structures, like proboscis proportions, punctuation of clypeus and mesonotum, sculpture of propodeal triangle, shape of hidden male sterna (S6-8) and male genitalia (Michez & Eardley in press). In general, the different species of Melitta are morphologically very similar when compared with other Melittidae s.l. (Michener 1981, Michez & Patiny 2005, 2006, Michez et al. 2004a, b, 2007a). Most Melitta show equivalent size and vestiture, while the largest Dasypoda is twice as large as the smallest species (Michez et al. 2004b).
The genus Melitta is recorded in three zoogeographic regions: Ethiopian, Neartic and Palaearctic. Melitta seems to be more diverse in the temperate and Mediterranean climatic regions of the Old World Region, like the Mediterranean Basin, the medio-european valley, the Chinese Sichuan and the south-western region of Africa (Michez & Eardley in press). In the Palaearctic and Nearctic they seem to be missing in the deserts, semi-deserts (e.g. Kyzyl kum), savannah and tropical forest. However, in Africa, M. albida, M. arrogans, M. danae and M. katherinae live in deserts, semi-deserts and/or dry savannah.