I've been trying to find the name for a bee (or fly?) that is frequent where I live (S. La.)

The wierd thing about these bees ... they range themselves around my home, about 3-6 feet from the outer wall, about 10-15 feet apart, and just hover there and watch the walls. Buzzing sentinals. Haven't bothered me or the dogs, and I've never seen them feeding or landing -- just hovering. They're aggressive to each other, quick to drive intruders away. This weekend I saw the same behavior at my sister's house, 20 miles away.

They're the size of what I call a "bumblebee" (not a honeybee, but the big black-and-yellow striped bee). They have a black shiny hairless upper abdomen, the thorax is covered with dull gold/tan hairs, and I haven't figured if the face is yellow, or if they've been into the pollen.

Because they've never yet bothered me, I'm hesitate to net one for a closer ID ... okay, I've seen too many Killer Bee movies, but I don't want to get put on their black list.

Anybody know what it is?