Hornets, I think
I just moved into a new home and have noticed these large hornets. They are eating the bark off of the lilac tree and are attracted to light at night. What should I do? Do you know where the nest would be? The ground or attached to something above ground?
This looks like European hornets. They are considered beneficial, as they eat lots of pest insects.
They like to feed on that sap of lilac. It is a common occurrence in our area, and usually the damage is not great. There is little you can do about them because it is rare to know where their nests are. They will die with the cold weather.
The hornets seem to favor the older lilac stems, so at the end of the season (after a hard frost), you could cut back the older stems of the lilac. Lilac takes rejuvenation pruning very well. Pruning will stimulate new stems to grow and the newer, younger stems tend to be less attractive to European hornets.
Here is our page about them: http://extension.umd.edu/hgic/european-hornets