This past Wednesday, members of the Lamp Lab headed out to southern Washington County to scout out streams to sample for black fly larvae. We were able to visit six sites where streams intersect different roads, as well as the Potomac River. At each site, we turned over rocks in riffles, and examined them closely for any larvae or pupae. We were able to find larvae at each site we visited, although for most of the sites, larvae were found exclusively on vegetation within the streams, and not on the rocks themselves. Black fly larvae typically will not be found on rocks that are covered with algae, and rocks at many of the sites we visited had dense growths of algae.
Finding black fly larvae in each of these streams is not unexpected, since there are many species of black flies that are commonly found in all kinds of streams. At this point we still don't know whether the larvae we collected belong to the same species of the flies that are swarming Washington County residents. And the adults were definitely swarming while we were sampling. We each experienced first hand the nuisance that the people in this area must deal with throughout warm weather seasons. We did also collect some of the adult flies, to begin to compare them against the larval species.