Plummers Island, Maryland has been studied by naturalists for over 100 years. The bees collected on the Island and the immediately adjacent mainland represent six families, 41 genera, and 232 species. About 20% (47 species) are parasitic and do not collect pollen. Most bees are generalist (polylectic) foragers, but there are a few species that appear to visit only a few species or genera of plants (oligolectic foragers). Three exotic species are among the fauna, including the European honey bee (Apis mellifera L.). Based on historical specimens in the collection of the National Museum of Natural History, Smithsonian Institution (USNM), and contemporary survey efforts, the number of bee species on the Island appears to have increased since the 1920s–1960s, and there is no evidence of local species extinction. It is possible that the use of Malaise and pan traps in addition to hand nets have increased collecting efficiency so that the increase in species richness is an artifact of collecting techniques rather than a biological phenomenon. Alternatively, increased species richness may reflect the resiliency of bees and an increase in available nesting sites as heavily shaded forests of the eastern United States have become open through deforestation and urbanization. While the vegetation of the Island has matured through natural succession, the surrounding Washington, D.C. metropolitan area has seen major urban, industrial, and infrastructure development and the resultant opening of forests, increasing bee habitat. Plummers Island is likely a refugium for surrounding bee populations.