Anthidium is the genus name for the very large group of bees that contains the wool carders. Wool carders are known as such because the females collect fibers by “carding”—or scraping—them from a plant. The female wads the fibers into a ball and then carries them back to her nestusually in a hollow reed or a nesting block. She then lines her nest with the fibers.
The male carder bee can often be seen jealously guarding a patch of flowers. He can be quite aggressive, fending off any interlopers by darting and chasing. If necessary, he will even wrestle a competitor to the ground—even bees much larger than himself, such as bumble bees and honey bees. Female wool carders are allowed into the guarded area to forage—in return for the chance to mate.
The native species here in the states is Anthidium maculosum. The bees are small, measuring one-half to three-quarters of an inch long. They are black to brown with white or yellow patches on their abdomens. The female carries pollen on the underside of her abdomen in a patch of hairs call a scopa.
A similar species, Anthidium manicatum, was introduced from northern Europe and has spread across the continent. The male of this species is even more aggressive, and is reported to actually kill bees that are competing for his territory.
You can expect to see wool carder bees in early summer. They will readily use nesting blocks with holes drilled 7-10 mm in diameter. Favorite forage includes sage, mint, catnip, lavender, Russian sage, and hedgenettle (Stachys).
As a general rule, bees are difficult to identify down to the species level, but with a little practice, you can become quite competent at the genus level. The wool carders are a good group to start with because both their behavior and their coloring are striking.