After a few months of work at the microscope, the Lamp lab now has preliminary identifications for the swarming black flies of Washington County. Our results suggest that the most likely source of the pest flies is the Potomac River. We found that this source has historical precedence, as a paper written in 1959 also found nuisance flies emerging from the Potomac. Later this winter, we will have our identifications confirmed by an expert taxonomist to make sure our findings are accurate.
With the identifications nearly completed, the Lamp lab had enough data to put together a presentation at the Entomological Society of America’s national conference in Austin, Texas. Below is a map and some of the results we shared at the conference.
Distribution of Adult Species
Sites where adult flies were collected are indicated by yellow circles on the map. Adult females belonging to the Simulium jenningsi species group were collected at all sites by our volunteers.
Distribution of Larval Species
19 different stream reaches were sampled, as indicated by the red circles on the map. Six larval species or species groups were identified. Only two streams contained larvae of S. jenningsi species group: the Potomac River and Antietam Creek. Sampling of the Potomac River was limited through much of the summer due to high water levels, however S. jenningsi was the only species group collected from this site. By contrast, Antietam Creek contained a lower relative abundance of S. jenningsi larvae, and also contained larvae of Simulium tuberosum and Simulium vittatum species groups.