Wikipedia:
"Eumenes is the type genus of the subfamily Eumeninae ("potter wasps") of Vespidae. It is a large and widespread genus, with over 100 taxa (species and subspecies), mostly occurring in the temperate portions of the Northern Hemisphere. Most species are black or brown, and commonly marked with strikingly contrasting patterns of yellow, white, orange, or red (or combinations thereof). Like most vespids, their wings are folded longitudinally at rest. The first metasomal segment is narrow and elongated, creating a "bulbous" appearance to the abdomen. The genus was named after the Greek general Eumenes."

Arizona Naturalist:
"Tiny vessels made of mud are the handiwork of this wasp, as well as some similar species. These mud pots are affixed to plant surfaces and contain captured and stung caterpillars together with a developing young wasp grub. By fall the wasps are looking to supplement their diet with nectar from flowers where they are a common site. They rarely sting people and are not aggressive. Each wasp makes its own pot and fills it with caterpillars - they do not form colonies or multiple nests. Vegetable gardeners should protect these beneficial insects by reducing pesticide use."