Sphex pensylvanicus, the Great Black Wasp. Although it's big, it's not aggressive the way some hornets and yellowjackets are. So don't be scared of it! The female captures katydids to feed to her young, but for herself she drinks nectar.
The ones I saw really loved the flowers of Spotted horsemint, Monarda punctata. This is a lovely and rather odd monarda which tolerates dry sandy spots like our High Park garden better than the more common red bee-balm. It's blooming abundantly now in the garden, and the Great Black Wasps prefer it above any other flower there.
This lovely 1815 picture of horsemint comes from the Botanical Register vol. 1 tabl. 87 from www.botanicus.org. The artist was the Welsh botanical illustrator Sydenham Teak Edwards (1768-1819). Click his name to find out more details of his immense contributions to botany, and the use of his designs in things like Spode china.
To see many more images of horsemint, try "monarda punctata" in Google Images. You'll see there is a wide variety of color forms.
As far as I know horsemint does not runner about the way bee balm does.