If you are sure you have Bald-faced hornets, they build large paper nests that hang from the open in trees. They mainly eat nectar and fruit juices from holes pecked in fruit by birds. They are a dangerous insect as they can sting flying backwards. They are actually beneficial as they also eat damaging caterpillars. If you drench the tree stumps with a mixture of soap and citrus products it should drive them away. If by chance they are yellow jackets, they tend to have underground nests. Hornets have darker coloring than yellow jackets and have skinnier waists. Yellow jackets are yellow and black.

It really is too bad that they are such a nuisance. They help control many nuisance pests. When we remove their hives in our bee suits it is quite interesting. The sound of a bald faced hornet hitting your veil at full speed is quite disconcerting, at times. We hardly get stung because of their hit-and-run tactics, plus, with the hive being aerial, they mainly aim for the head and shoulders which is where we generally have great protection. Yellow jackets, on the other hand, are rather irksome. Their numbers tend to be greater, they like to sit and sting, and they always aim low because of their subterranean hive location. I call them 'ankle-biters'. They like to work their way under my suit where it meets my boots and have fun in my socks. : ). A little advice, avoid the flight path, wear light-colored clothing, and if you have to work around them, choose the cooler periods of the day...dawn and dusk. The light colored clothing is helpful because it is not a recognized 'threat' color. Most threats they deal with are predominantly dark colored.

Here is a link that might be useful: Bee removal site