Hornets boring holes in willow tree
Hello. I have some sort of large hornet boring holes in my willow tree. As far as I can tell the tree is otherwise healthy. I am attaching photos of the wasps and of the holes. Can you please tell me how to get rid of these insects? We really want to save the tree. I also want to mention that the tree is near our duck pond. I don't want to use any insecticides that can poison them or the frogs that live in the pond.
The holes in the trunk of the willow oak have been made by sapsuckers or woodpeckers. http://extension.umd.edu/hgic/woodpeckers-and-sapsuckers
The insect looks like a European hornet and they are not borers. European hornets feed on a large variety of insects. Workers will also girdle twigs and branches of trees and shrubs (especially lilac) to feed on sap. Most likely they are attracted to the sap. No control is necessary. http://extension.umd.edu/hgic/european-hornets