The female builds a miniature pot out of mud in which it lays an egg and places a live caterpillar. Its developing larva feeds on this whereas the adult wasp feeds primarily on nectar. Wasps in the genus Eumenes can be recognized by the fact that the first abdominal segment is long and slender, very thin at the front and widening towards the back. Eumenes fraternus is about 15 to 20 mm long and is similar in appearance to other members of the genus. Its coloring is black with a scattering of ivory-colored markings. The forewings are 8 to 10.5 mm long in the male and 10 to 12.5 mm in the female. It has shorter pubescence on the first segment of the antenna than do the otherwise similar E. crucifera and E. verticalis.
Found in glades, rough shrubby areas and forest verges, typically from April to November.