There were at least two individuals, one of which was larger and presumably the female. Both were at the bee balm on and off for hours. From what I observed, they were stealing nectar, as they appeared to be cutting the bottom of each floral tube.

There are holes in the concrete wall behind this garden, as well as a border of rocks in sand (in which there is a large colony of cicada killers). I will see if I can observe where they may be nesting tomorrow.