myk1 nailed it - carpenter bee. Found this on a page about blueberry pollenation "Carpenter Bee (family Xylocopidae) often resemble large bumble bees. These insects use their strong mandibles to excavate nesting holes in wood. They are often seen flying around old packing sheds or other wooden structures. Carpenter bees visit blueberry flowers, but they cut a hole near the base of the corolla and "steal" nectar. Since they never make contact with the stigma, pollination is less likely to occur. Honey bees quickly learn to use these holes and also become "nectar robbers". The southeastern blueberry bee and other native bumble bees have not been seen using the robber holes. They continue to pollinate flowers that have been damaged by carpenter bees. A carpenter bee can be distinguished from a true bumble bee by looking carefully at its abdomen. Bumble bees always have a dense coat of hair over the entire abdomen, giving them a very fuzzy appearance. Carpenter bees, in contrast, have little or no hair on their big black bottoms!"

I have hundreds of these bees on my caryopteris and other flowers. Where do they live? In a hive, in my house, in the ground? I see them sleeping at night right on the flowers.

i was thinking/hoping that it was just the empty nest syndrome! they nested between the exterior and interior wall of my shed/ old pigeon coupe. north wall, of course! their entrance was right above the top corner of the doorway. very convenient :) this is the same entrance the bb's used two years ago. i thought they were there later in the season than this. they certainly had more activity than this years. i am worried b/c it has been very dry, it is an old nest that may have disease (?), and there has been pesticide sprayed (limited) and grain form sprinkled on the ground, as well as soapy water for individual insect control on veggies. i know that bees are extremely sensitive. i may just be overreacting since i simply haven't had the time to observe the activity in a few weeks. i have lavendar and echinacea which i know they like. also, lamb's ears which is just starting to bloom. oregano also just starting to bloom. i am not sure if they visit cilantro- pests leave this alone so it has not been sprayed with anything. this spring i had a queen visiting a box in our garage continuously. i finally realized she was collecting fuzz off one of dh's hunting gloves made of that fuzzy flannel type stuff. i had to stand ground for her! last year, dh sucked a queen up in the shopvac thinking she was going to nest in the garage b/c she kept going in there. so, this ;year i told dh if he is so worried, put his gloves away where they belong and leave queeny alone! :)

Don't worry, at this time of the year bumbles are done, most are dead now, some Queen bumbles who start the whole cycle again next year already have appropriate shelter in holes in the ground, buildings, sheds, walls etc. Konrad