Yellowjackets are black-and-yellow wasps of the genus Vespula. Like other vespids, they live in colonies and build globular paper nests. Workers are around 12-20 mm in length, depending on species, and feed on nectar, while chewing other food for their young. They sting repeatedly with relatively little provocation, and so can be major pests, especially in the fall when food becomes scarce.
The baldfaced hornet, Vespula maculata, belongs among the yellowjackets rather than the true hornets, but is not usually considered one because of its ivory-on-black coloration.