This Plasterer bees (Colletes sp.) appeared late in august on the blooming Giant goldenrod (Solidago gigantea). Both are males, but the necessary details to identify them were unfortunately not present or unclear on the photographs.
Most of the characteristics to identify the males are located at the sternites, the segments on the abdomen underside .
Based on the time of the observationa and the location I suspect either Colletes daviesanus or Ivy bee (Colletes hederae). The plant the species is foraging on here is probably less important because it is a nectar visit, but other species of goldenrod have been related to these bee species in other observations, like for example as mentioned on Wildebijen.nl.
A C. daviesanus female was already actively nesting in the bee hotel for some time and was still present at the time of these observations.
One of the males is recognizable by an interrupted hairband on tergite IV.
References1 SMIT, Jan. Determinatietabel voor de bijen van het genus Colletes in Nederland. Bzzz/HymenoVaria, 2009, 30.1: 65-68.