This essay charts the career of the entomologist and popular author Marston Bates (1906-1974) within the Rockefeller Foundation (RF) between 1935 and 1952. Today, Bates is best remembered as a science communicator. Publishing over a dozen books on natural history and the environment, he helped bring ecological ideas to broader public audiences during the 1950s and 1960s. Not simply a popularizer of contemporary scientific concepts, Bates stood out for his critical commentary on the environmental problems of economic development, conservation, and global population growth, as well as the need for more integrative, cross-disciplinary approaches to understanding humans in nature. Long before becoming a public intellectual, however, he worked for the RF as a mosquito specialist, serving as director of International Health Division malaria and yellow fever laboratories in Albania, Egypt, and Colombia during the 1930s and 1940s. Bates' mid-career shift from researching mosquito ecology to writing about human ecology may seem to be a sudden left turn. A closer look at the archival record reveals the pivotal role played by the Rockefeller Foundation in shaping Bates' career trajectory and ideas about the environment. Furthermore, placing Bates' work in the context of his time with the RF reveals connections between twentieth-century U.S. environmental thought and international health projects.