How do you get rid of bumblebees?

I realize that bumblebees are helpful to nature and are non-aggressive but recently we have discovered that our new back yard is infested with some 20 bumblebees. They don't seem to go anywhere as far as foraging for pollen goes (there are no flowers of any sort in my yard) and have become quite a nusance to me and my pets. I haven't been able to mow my lawn so I can't locate a nest and I'm tired of them hovering in front of me with that "wha's your problem buddy" look. Is there any way I can treat them without knowing where the nest is? Like a bee trap or something?