The family Andrenidae is a large cosmopolitan (absent in Australia) non-parasitic bee family, with most of the diversity in temperate and/or arid areas (warm temperate xeric), including some truly enormous genera (e.g., Andrena with over 1300 species, and Perdita with nearly 800). One of the subfamilies, Oxaeinae, are so different in appearance that they were typically accorded family status, but careful phylogenetic analysis reveals them to be an offshoot within the Andrenidae, very close to the Andreninae.
They are typically small to moderate-sized bees, which often have scopae on the basal segments of the leg in addition to the tibia, and are commonly oligolectic (especially within the subfamily Panurginae). They can be separated from other bee families by the presence of two subantennal sutures on the face, a primitive trait shared with the sphecoid wasps. Many groups also have depressions or grooves called "foveae" on the head near the upper margin of the eyes, another feature seen in sphecoids, and also shared by some Colletidae. Andrenids are among the few bee families that have no cleptoparasitic species. There are also a very large number of taxa, especially among the Panurginae, whose sting apparatus is so reduced that they are effectively unable to sting.
The subfamily Oxaeinae is rather different in appearance from the other subfamilies, being large, fast-flying bees with large eyes, resembling some of the larger Colletidae.
Andrenidae is one of the four bee families that contains some species that are crepuscular; these species are active only at dusk or in the early evening, and therefore technically considered "vespertine". In the Andrenidae, such species occur primarily in the subfamily Panurginae. These bees, as is typical in such cases, have greatly enlarged ocelli, though one subgenus of Andrena that is crepuscular has normal ocelli. The other families with some crepuscular species are Halictidae, Colletidae, and Apidae.
The mason bees are small to medium-sized bees that are distinguished by two subantennal sutures below each antennal socket. There are about 1300 species known to exist in North America
Andrenidae usually have two prominent sutures below each torulus. These sutures are obvious if the integument is lightly pigmented, but often they are invisible if the integument is black. The glossa is acute and the labial palpus usually has identical segments (Finnamore & Michener (1993).
There are more than 2,000 species identified by the year 2010, with about 1,200 occurring in North America. Two subfamilies are Andreninae and Panurginae. They nest in burrows in the ground, and their burrows are similar to those of the halictids; sometimes large numbers of these bees will nest close together in areas where there is little vegetation.Most are solitary, but some are also communal. They are not known to be parasitic
Other key references are Hurd (1979), La Berge (1986, 1987, 1989), Hirashima (1952, 1966) and Osychnyuk (1977.