I watched a three way fight over some heirloom roses today. On one rose it was between one of my honey bees, a bumblebee, and a hornet. They threw the honey bee off the rose (still alive), and the hornet and bumblebee duked it out - the bumble bee winning. The bumble bees are chasing any other bugs off the flowers rather aggressively. I've watched them all share before but have never seen this behavior before. :?
Are you sure it was a bummble bee. The males of certain species of solitary bees can be very territorial...
"A male carder bee, Anthidium manicatum, rests on his territory, a meter-square patch of Lamb's ears, Stacys lanata, in England. THis is the most aggressive territorial bee known. Males often kill or maim worker honeybees which enter their territories. By deterring other males and chasing away other insects, he enhances the attractiveness of his territory to females by mantaining a protected food resource." p. 162, "Bees of the World" by Christorpher O'toole and Anthony Raw
As I said, maybe that bee was a relative of this species. If you like, I can post the photo that went with that paragraph.