Earlier this summer the Lamp Lab investigated reports of gnats/black flies from all the way in Cecil County. Having conducted most of our research in western Maryland, travelling out to the northeast corner of the state to find black flies was a change of scenery for us.
Our area of interest in the county was very close to the Pennsylvania border. We had heard from Pennsylvania's Black Fly Suppression Program that right across the border in their state was also a region of high black fly nuisance. Although we were initially curious if the flies reported in Cecil County were a recent result of changes in the Pennsylvania program, we were informed the flies had been a problem in that region of Maryland for over a decade.
We collected both larval and adult black fly specimens. The larvae were collected from Octoraro Creek in a section near the town of Rising Sun. The creek had a lot of vegetation when we visited in June, both in the form of aquatic plants and overhanging tree branches. We found large numbers of larvae attached to the aquatic plants and the dead leaves trapped between rocks. These samples did contain a majority of Simulium jenningsi larvae, our pest species of interest in Maryland. Although we stopped by to sample a section of the Susquehanna, the largest river in the area, we did not find any habitats that contained larvae. It is possible the larvae may be in the river in places we could not access, but we can at least confirm that the Octoraro does serve as a source of S. jenningsi.
Adult flies were collected from a pull-off along a road reported to have a nuisance problem in Rising Sun. When we first got out of our truck, the flies were quite apparent. They continued to provide a moderate nuisance to us as we measured the temperature, humidity, and light intensity at the location. The wind started to pick up as we began sampling the flies with our aerial nets, which felt great to us but unfortunately dispersed the flies. However, we were able to collect adult specimens from that pull-off and identify them in the lab as S. jenningsi.
In summary, S. jenningsi is indeed in Cecil County, and appears to be the cause of gnat nuisance in that region. One likely source of the flies in the area of Rising Sun is Octoraro Creek, based on the number of S. jenningsi larvae collected there, but we have not ruled out the Susquehanna as another possible source. We hope to hear from more Cecil County residents in the future to get a better understanding of how the flies are affecting the communities there.