Brown-Belted Bumble Bee Male – Bombus griseocollis
I found one day, on top of a windswept hill, a large group of male bumble bees congregating on the branches of a small tree, and flying aggressive sorties investigating and harassing every flying insect that happened by. I have never seen so many free-flying male bees all in one place.
The male bees are very territorial and challenged everyone except their own bros – but they really flew in search of virgin queens with which to mate.
Each bee had a favorite resting spot and returned to bask after every foray. It was an enchanting time nestled under that low-growing tree with all these huge insects buzzing about. I don’t know if any of them were successful; I never saw any females.
Robber flies in genus Laphria are famous bumble bee mimics, as are some flies in family Syrphidae. Big business, this mimicry.
Reference: Bugguide.net, Bombus griseocollis
North American Insects & Spiders