The USNM Diptera collection comprises some 3,200,000 pinned specimens representing some 55,900 species, more than 600,000 slide-mounted specimens, and some 22,000 primary types. A genomic collection with currently more than 2,500 specimens preserved in liquid Nitrogen is growing steadily. Although there is material from all biogeographical regions, the New World is best represented. Of the 162 currently recognized families of Diptera (sensu Pape et al. 2011 + recently described) all but Heteromyzidae, Inbiomyiidae, Oreoleptidae, Ulurumyiidae, and Valeseguyidae are represented.
Graduate students pursuing research about Diptera are encouraged to apply for money through the Williston Diptera Research Fund, a special endowment created for the increase and diffusion of knowledge about Diptera.