Male bumble bees
A key early decision point when identifying bumble bees is to confirm whether the individual bee in question is (1) a female or queen (corbiculum), a male (drone) or a cuckoo queen.
One field mark is the shape of the tibia on the rearmost leg. If the tibia is flattened or holding a pollen basket the individual is a female or queen.
If the rearmost leg of the bee is instead more rounded and hairy, with no evidence of carrying pollen, then it may well be a male.