Image Credit: S. Rae
Cuckoo Sweat Bees: (Halictidae: Sphecodes)
small to tiny cuckoo-bees are usually very densely and coarsely punctuate, have red abdomens in the female and black-tipped abdomens in the male (sometimes all black). They are parasites of the typical sweat-bees. They are inadequately studied to identify to the species-level of resolution, but probably there are at least 3 dozen species in the PNW. They spend very little of their active time visiting flowers for nectar.
Male (left) and female (right) Sphecodes. Sphecodes is the second most abundant group of parasitic species that you are very likely to encounter.