The wool carder bees Anthidium Fabricius are back, and right on schedule.
Their flight season is from May to October, and since this is May, it's a good sign.
Their favorite plants in the garden, the lambs' ears stachys, are shooting up stems that are slowly developing tight whorls that will open up within a month, with purplish flowers full of nectar for the bees.
Honey bees are the most frequent visitors to the flowers, but the wool carder males get very territorial about the lambs' ears and try to chase away the other bees.
These bees are also commonly called "cotton bees" because the females scrape hairs off surfaces of hairy leaves and stems and stuff the hairs into their nesting cavities. The hairs form a filling where pollen "loaves" are made, upon which the bees lay their eggs.
In this photo, which unfortunately is blurry, you can see the same bee forming from the underside of a lambs' ear leaf a ball of fiber between her legs.