These are European Hornets, a very common large wasp which is seen most frequently in late summer and autumn. Below are links with information and some comparative images of the two hornet species. European Hornets are non-native, but have been in the country for over a century.

The behavior of chewing-off bark from lilac (which seems to be a favorite) and other trees and shrubs is typical for this time of year. They are either using the wood fibers to build more papery nest layers or are feeding on the sap that oozes from the wound. (Possibly both, plus perhaps hunting any other insects also drawn to the sweet sap, because they feed these insects to their young.) Social wasp colonies are at their largest this time of year, so there are many mouths to feed, though cooling autumn weather will soon be causing the social order in the nest to fall apart, and individual workers will wander off and soon die. Nests are abandoned by the end of the season and not re-used from year to year.

You don't need to do anything except to give the wasps a wide berth. They don't seek to sting unless they perceive a danger to their nest or themselves individually. Sometimes, they merely "bluff charge" an intruder to scare them away, or fly near you to investigate if you're a threat. (Try not to swat. It's often our loomingly large size or shadow, rapid movements, carbon dioxide breath wafting over them, or perhaps vibrations/vocalizations or other odors that catch a wasp's attention when they become alarmed at our presence.) Any damage done to the lilac or other plants tends to be minor and inconsequential, and if any stems die back as a result, just trim them down. Fortunately for lilac in particular, it's the older stems that should be pruned back periodically anyway to keep it regenerating for best growth and flowering.

https://extension.umd.edu/resource/european-hornets

https://extension.umd.edu/resource/asian-giant-hornet

 
Miri