Ammophila nigricans (Thread-waisted Wasp)
I saw this chap on the gooseneck loosestrife (Lysimachia clethroides) but at first is wouldn’t come close. I stood for a while without taking any pictures and eventually it came near. I managed to take quite a few pictures but most of them either aren’t in focus or don’t show enough of the wasp to identify it. This is an Ammophila nigricans, one of the thread-waisted wasps. It’s a fairly large wasp and, as you can see, is characterized by a long, very narrow “waist” and the brown coloration on its abdomen.