This fascinating species of bee (Anthidium manicatum) have very distinct behavior and there are some plants worth growing specifically to attract them.
The males find a patch of plants they particularly like - normally because they expect it will be popular with the females - and set about patrolling this patch as their territory. They can be seen darting about and chasing off other bees that might dare to come along. They will even take on bumblebees that are double thier size. The females are allowed in to forage in return for a chance to mate.
In addition to the normal foraging for nectar and pollen the females also collect hairs (cards) from certain plants that they use to line their egg cells. These plants include stachys byzantina (lambs ears) and hairy verbascums (mulleins).
At rosybee this summer I have been watching wool carder bees fighting over a patch of stachys officianalis (betony) and only occasionally on the stachys byzantina. The former, as far as I can tell, is not hairy and so I guess they are simply defending a prime nectar source.
They move so fast that photography is difficult but I did manage to catch the above picture. One of the other distinctive aspects of their behavior is that they are able to hover which is really unusual in bees and can help identification if they dont stop long enough to see them close-up.