Andrenidae

The family Andrenidae is a large (nearly) 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 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.

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.

"Nocturnal" species
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". These bees, as is typical in such cases, have greatly enlarged ocelli. The other families with some crepuscular species are Halictidae, Colletidae, and Apidae.