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.

Jean Henry Fabre was fascinated by the architectural prowess of Eumenes found in France. By all means follow the link and read some Fabre.