Different types of wasps and hornets build various types of nests. When you find one, "What kind of wasp made that?" may be the first question you ask yourself, and it's one you can answer after a little research and detective work. Trying to find a wasp or hornet that inhabits the nest will yield you quicker identification results, but characteristics of the nest such as size, exposed or unexposed, location and height can help you determine at least which family the wasps or hornets belong to.
Study the location of the nest. Some hornets, such as the bald-faced hornet, build aerial nests in trees; some wasps, such as paper wasps, build nests on or in your house; and some wasps and hornets, including yellow jackets, build their nests in the ground.
Look for exposed cells. The cells are the familiar honeycomb shape like those of a honeybee nest. The cells house the eggs, larvae and pupae until adulthood. Paper wasps have exposed cells on the bottom of their nests, and their nests resemble umbrellas. Bald-faced hornets protect the cells from the elements by building a large papery shell around the outside of the whole nest.
Notice any special characteristics such as size or material. Mud daubers construct single tubes out of mud on vertical surfaces. Each tube holds one egg that will hatch and feed on spiders the mother has stuffed in the tube. Bald-faced hornet nests are usually up high, but sometimes they are hidden in shrubs or under the eaves of a house. They are sometimes as large as a basketball, gray and look like a hanging pear-shaped paper ball. Both the domestic and European paper wasp species build the umbrella-shaped exposed nest, but European paper wasps build them much larger and can have colonies numbering well into the thousands.
Keep a distance of about 30 feet and look to see what types of wasps or hornets are going into the nest. Wasps, such as paper wasps and mud daubers, have very slender waists and rear legs that hang during flight. Hornets, on the other hand, are typically more stout-bodied and hold their rear legs close to their bodies in flight. Use binoculars for a look from a safer distance.
TL;DR (Too Long; Didn't Read)
Wasps and hornets are beneficial insects, not typically pests. Unless the nest is dangerously close to a high-traffic area such as an exterior door on your home, in your home or other area, it is best to leave the nest alone.
Mud daubers rarely sting. Bald-faced hornets and domestic paper wasps are reluctant to sting and rather docile, as long as you don't disturb the nest, get too close or accidentally crush one. Yellow jackets are aggressive, eager to sting to protect their typically in-the-ground nests. European paper wasps are also eager to sting, and each sting leaves a chemical attractant for the other colony members to sting you, as well.