Numbers
Nearctica lists 8 species plus 3 of "other authors".
About 330 species worldwide.
Identification
The hair bands are apical, not basal (like many Andrena but unlike most Lasioglossum)
Wing veins all strong (versus one or more apical crossveins conspicuously weak in Lasioglossum females).
OVERVIEW OF SPECIES
♀  
♂
♀  
♂
♀  
♂
♀  
♂
♀  
♂
♀  
♂
♀  
♂Habitat
general; particularly numerous in sandy areas
Season
Early spring-late fall; all year in Florida and south Texas
Remarks
Most Lasioglossum species were described in genus Halictus when this was defined much more broadly to include most non-parasitic Halictini.
Many species are eusocial with groups ranging from 2-4 females to more than 200.