Jee the names of some those insects are really nice:
Bombus fraternus (fraternal)
Bombus perplexus (perplexed?! maybe the classifier was perplexed in classifying it)
Bombus vagans (going round, wandering)
Bombus frigidus (cold or even "frigid")

PS Bombus pennsylvanicus cannot be confused with a carpenter bee because the latter would have a totally black abdomen, besides being "hairless". PE observed lots of fur, yellow and black, so they must have been bumblebees.