This is a halactid bee. They are pollinators and will also come to the honeydew secreted by aphids. By the way, it looks like I have never posted on the woolly aphid colonies that inhabit beech tree branches, so look of that coming soon. Anyway, I kind of wanted this insect to be a cuckoo wasp because they are parasitic to other bees and wasps and it would be really cool to see one! Oh, well, i'll just have to keep my eyes peeled.