Tue, Apr 21, 2009 at 7:03 PM
This is mid-April in Concord, CA. These guys seem to stake out a territory. This one hovers near the potted Asparagus Fern and the geraniums. Another hovers around the white Lilac. They chase others of the same species and then come back to their hover spot. They are there all day, day after day. They are quite bumblebee like, in that they are black with yellow thorax and shiny black abdomen. They make a buzzing sound and they don’t seem at all aggressive or concerned about human presence. There are citrus trees in bloom on the property, though not sure these are active in those flowers.
Concord, CA 94520
Your photo resembles a Carpenter Bee and the behavior you describe is similar to the behavior we have witnessed in male Valley Carpenter Bees staking out territory and hoping to attract mates, but male Valley Carpenter Bees are an overall lovely golden color. We consulted BugGuide, and we believe your specimens are a related species, Xylocopa tabaniformis.