A study of behavior and structure indicates that highly eusocial behavior arose twice in the bees--i.e., in the stingless bees (Meliponinae) and in the honeybees (Apinae). Morphological features demonstrate the distinctiveness of these two groups and the relationship of the latter to bumblebees (Bombini) and orchid bees (Euglossin). The social behaviors of the stingless bees and honeybees, while more or less equally elaborate, are so different as to support their independent origins. The primitive apids, along with the related Xylocopinae (in the Anthophoridae), appear to have had the potential for parasocial, subsocial, and primitively eusocial behavior and from such forms the two highly eusocial groups arose.