Bald-faced hornets are those large white and black wasps you see this time of year now that their nests are getting pretty big. At this point, their nests are probably about the size of a basketball or larger and house anywhere between 50-150 wasps. https://www.pestworld.org/pest-guide/stinging-insects/bald-faced-hornets/
They’re not hornets, but get that name because of their size and similarity to hornets. They are actually members of the Yellow Jacket family, making their nests in similar social fashion. The bald-faced hornet nest almost always has a hole at the bottom of the nest and is made of thicker out walls.
They make the nest by using wood pulp (wood and saliva) from wood in the forest most often and like a ball of clay, they will use their mandibles and front legs to attach and flatten the ball along a strip of the nest wall. Each ball of wood pulp comes from a different wood source which gives it the different colors of strips and segments in the nest when you look at it.
They continue building the nest throughout the summer until winter. By then, the queens that have been born will mate and leave the nest to find a place to overwinter before starting the whole process next spring.
On hot days, you may see one or several on the nest just flapping their wings. This is a way they control the temperature inside the nest. They have to keep temperatures from affecting the growing larvae and pupae.
If you see one, it’s a good idea to steer clear. These wasps are often referred to as, “the bad ones”. They are bigger, and they can sting, and hurt. Once a nest gets bigger than a softball, we always recommend leaving it to a professional who understand how they work and behave. And, if you do find that need, we can help. In the mean time, stay cool, and stay safe.