He was a senior insect taxonomist with the United States Department of Agriculture. Rohwer wrote Technical papers on miscellaneous forest insects. II. The genotypes of the sawflies or woodwasps, or the superfamily Tenthredinoidea. Technical series US Department of Agriculture, Bureau of Entomology, Washington, DC 20: 69–109 (1911) and very many papers describing new species of Hymenoptera. His collection is held by the Smithsonian Institution Washington D. C.