Andrenids tend to be small- to medium- sized ground-nesting bees. They are solitary, meaning that the queens nest alone or in aggregations and do all the work of nest construction and provisioning by themselves. In fact, once the queen has dug her nest, foraged for food, provisioned the nest and laid her eggs, she frequently perishes before the maturation of her offspring .
As a group, andrenids are very successful. They are the most species-rich family in North America,  and they are found on all continents except Australia .
A key taxonomic character of the andrenids is the occurrence of two subantennal sutures running from each antennal socket to the clypeus . Unfortunately, you can’t see this characteristic without the aid of a microscope. Easier to see, perhaps, is the relatively dorsoventrally flattened aspect of andrenids, their flattened heads as a consequence of facial foveae (i.e. concave regions with minute hairs) on the insides of their eyes, and their oval vs. parallel-sided abdomens .
1. Michener, 2007
2. Stephen et al., 1969
2. Michner et al., 1994
3. Stephen et al., 1969