Black flies in Cecil County

 The general location of our sampling in Cecil County.

The general location of our sampling in Cecil County.

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.

 A section of Octoraro Creek near Rising Sun, MD. The vegetation in the water was covered in larvae.

A section of Octoraro Creek near Rising Sun, MD. The vegetation in the water was covered in larvae.

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.

Black flies in Montgomery County

Early this past summer we received a report of nuisance gnat swarms from Montgomery County.  The gnat specimens sent to us from Silver Spring were indeed our black fly species of interest, Simulium jenningsi. This is not the first S. jenningsi female identified from this county. In the summer of 2014 members of the Lamp lab incidentally collected a S. jenningsi specimen in Silver Spring while searching for kudzu bugs. However, as we have learned from our sampling in Frederick and Washington counties, presence of S. jenningsi does not necessarily indicate large enough populations to form a nuisance problem to residents. So the complaint report in addition to the collected specimens provided us with new information.

This made us wonder, if S. jenningsi was causing a nuisance in Silver Spring, where else in the county could it be a problem? Over the summer we sampled for black flies at twelve locations throughout Montgomery County. We specifically targeted parks and walking trails, as these are places where residents and tourists are likely to notice nuisance flies while enjoying the outdoors. Of these twelve parks we encountered and identified S. jenningsi from eight, their locations and the location of the resident-collected specimens shown in the map below.

 Known locations of adult S. jenningsi in Montgomery county, Maryland from the summer of 2015.

Known locations of adult S. jenningsi in Montgomery county, Maryland from the summer of 2015.

None of the Montgomery County sampling trips resulted in S. jenningsi numbers close to the worst we have experienced in parts of Washington County, designated as a "Level 3," or an extreme nuisance, on our 0-3 nuisance scale. However, three locations did reach "Level 2," a moderate nuisance, which is the level we would expect most people to start noticing and feeling annoyed by the swarming black flies. These locations were in Wootton's Mill Park in Rockville, Seneca Creek State Park in Gaithersburg, and Ken-Gar Palisades Park in Kensington. One of our field technicians was unfortunately more attractive to black flies than the rest of us, and found Wootton's Mill to be particularly unpleasant that day regardless of the plentiful in-season wineberries.  

 Wineberries at Wootton's Mill Park in Rockville

Wineberries at Wootton's Mill Park in Rockville

 Picnic area at Seneca Creek State Park in Gaithersburg

Picnic area at Seneca Creek State Park in Gaithersburg

 Our standard black fly sampling equipment strewn about at Ken-Gar Palisades Park in Kensington

Our standard black fly sampling equipment strewn about at Ken-Gar Palisades Park in Kensington

Black fly numbers can be highly variable day-to-day. As such, it is very possible that the parks we sampled could have a higher nuisance level on some days, or times of day, than what we experienced. What this map does tell us is that female S. jenningsi can be found to some extent in many areas of Montgomery County. Although we did not collect any specimens from the western or eastern corners of the county, it appears very likely that S. jenningsi can travel from their aquatic breeding site to these regions. Reports from residents in these areas will provide us with a clearer indication to the accuracy of this assumption.

Regarding breeding locations, as we have learned from previous years the Potomac River is the most productive body of water for S. jenningsi larvae in Frederick and Washington counties. In the late 1950's, S. jenningsi larvae were very abundant at sites within the Potomac River bordering Montgomery County (McComb and Bickley 1959). Although we were unable to find larvae at the locations we visited in this stretch of the Potomac in 2015, we were limited in our ability to access the river for most of the summer due to high water levels. We hope to continue searching for larvae in the Montgomery-bordering regions of the Potomac in 2016 to determine if the larvae can still be found in their historic distribution.

McComb, C., and Bickley, W., 1959. Observations on Black Flies in Two Maryland Counties. Journal of Economic Entomology 52:629-632.


Spreading the word on black fly/gnat nuisance through UMD newsletters

"Gnats" are a fact of life to many farmers and residents of western Maryland, but few people may know what species is bothering them or where they come from. A new article has been published in two of the University of Maryland's extension newsletters to spread the word on Simulium jenningsi to Maryland  agriculturists.  You can find the article in both the 2015 Agronomy News issue 4 (here) and the 2015 Vegetable and Fruit News issue 4 (here).


New black fly/gnat informative flier!

 Sampling for black flies can be a strange sight. Photo credit Chloe Garfinkel.

Sampling for black flies can be a strange sight. Photo credit Chloe Garfinkel.

Swinging a large bug net over our heads can often get us curious looks and questions from people at our sampling sites. Although most people understand immediately when we tell them we're sampling "gnats," it can be a bit harder to explain what a black fly is. This is especially true in areas where the black flies are not a nuisance problem. To help with the outreach aspect of our research, we have developed a new informative flier about Simulium jenningsi and general black fly biology. 

If you would like to print out a few copies to give to you friends and neighbors, please download the PDF below.

Simulium jenningsi is back for the summer

Spring is fading into summer here in Maryland, and the Lamp lab has confirmed that our resident gnat, Simulium jenningsi, is back for the start of the season in Washington County. Reports of black fly swarms reached our lab earlier this month. After identifying specimens from these early swarms collected by a volunteer, we found that the flies were indeed S. jenningsi. S. jenningsi has several generations per year, and as we learned from our 2014 sampling S. jenningsi can be found in Maryland well into November. 

Further north into New England, the major nuisance black flies are in the genus Prosimulium. These flies bite a lot harder than S. jenningsi, but have one generation per year and are only around for a few weeks in the spring. Last year we collected Prosimulium adults in April in Washington County. While these flies were also caught flying around our heads, their numbers were not nearly as large as what we have seen with S. jenningsi.

With the return of S. jenningsi, the Lamp lab is getting ready for a new year of sampling. This year we will revisiting old larval and adult sampling locations, expanding our study into Montgomery and Prince Georges Counties, and testing out novel methods of surveying larval populations. Stay tuned for updates!


Discovery of more larval breeding locations

This summer the Lamp lab sampled for black fly larvae in over 25 locations along the Potomac River and its larger tributaries. As we learned from last year, the problem species Simulium jenningsi is found in at least one location each in the Potomac and Antietam Creek. Our preliminary larval identifications from this summer have now increased the total of known S. jenningsi larval locations to five in the Potomac, and one each for the Shenandoah River, Monocacy River, and Antietam Creek. 

 A map of the locations of larvae identified as  S. jenningsi   collected during 2013 and 2014, represented by black triangles.

A map of the locations of larvae identified as S. jenningsi  collected during 2013 and 2014, represented by black triangles.

When it comes to identifying black fly larvae to species, bigger is always better. The larger "mature" larvae, or those very close to pupation, have darkened gill spots. These gill spots are then dissected in our lab, put on a slide, and magnified in order to count the number of filaments, or branches, in the gills. S. jenningsi has 10 filaments per gill, while the nearly identical, but harmless, Simulium luggeri has 12 filaments. Several locations we sampled contained only small larvae without developed gill spots, which can not be identified to species with just a microscope. Therefore, it is highly likely that more of the locations we sampled in the Potomac contain S. jenningsi than we are currently aware of. 

In the future we hope to clarify both the species of these smaller larvae through DNA analysis, and which spots are the "worst" by estimating the density of the larvae at each location.

Black flies featured in The Maryland Entomologist

The Lamp lab is getting the word out about black flies to Maryland insect enthusiasts. The latest edition of the Maryland Entomologist, the yearly publication of the Maryland Entomological Society, features an article written by several member of the lab regarding the black flies of Washington County. This paper summarizes the work done during the summer of 2014, both by us and by our resident volunteers. 

The main findings of the paper include the species of the nuisance fly, Simulium jenningsi, and the results of our stream surveys which found these larvae within Antietam Creek and the Potomac River. These were great points of preliminary data for our current study, which looks in depth at where both the larvae and flies are found throughout the region.

If you are interested in seeing how our previous result write-up has evolved, please download the PDF of the article below.

Larval sampling in large rivers

 Looking out at the Potomac River before larval sampling. Photo: Claire Weber

Looking out at the Potomac River before larval sampling.
Photo: Claire Weber

Throughout this summer, the Lamp lab has been searching for larvae in the large rivers and creeks throughout Washington county, Frederick county, and a small corner of West Virginia. As of early August, the lab has found black fly larvae from 11 sites in the Potomac River, 2 sites in Antietam Creek, 2 sites in the Monocacy River, and 1 site in the Shenandoah River. However, the presence of black fly larvae does not necessarily mean the presence of Simulium jenningsi, our problem gnat. As we learned from our sampling last summer, there are at least 9 species of black flies in the region, and only S. jenningsi was found to bother people. We will know for sure which of these sites harbor the nuisance larvae when we identify them to species this fall. 

The lack of rain this summer was a bonus for our project. Water levels in the Potomac dropped earlier this year, allowing us to sample extensively during July, including at some sites that were mostly inaccessible last summer. Larvae were particularly abundant on plants and rocks in the shallow, fast flowing regions of the rivers. Deeper, slower moving areas of water, including near the Maryland side of the Appalachian Trail bridge, we were unable to find larvae at.

 Appalachian Trail across the Potomac Photo: Claire Weber

Appalachian Trail across the Potomac
Photo: Claire Weber

 Antietam Creek Photo: Alison Post

Antietam Creek
Photo: Alison Post

 Monocacy River Photo: Alison Post

Monocacy River
Photo: Alison Post

As the summer wraps up, we will complete our 2014 larval survey of the region by checking back at some of the relatively smaller creeks, including Israel Creek, that may still contain S. jenningsi. In addition, we will be revisiting some of the most productive sites we found this summer to see if any noticeable changes have occurred to their larval populations.

Swinging nets in June

 Collecting black flies with an aerial net.  Photo: Bill Lamp

Collecting black flies with an aerial net.

Photo: Bill Lamp

During mid-June, the Lamp lab sampled an ambitious 125 locations for adult black flies throughout our area of interest in western Maryland, with some visits across the river into Virginia and West Virginia. Our sampling spots ranged from state forests to mall parking lots and suburban sidewalks. The large bug net gained us several odd stares, but swinging a net over someone's head is actually a standard sampling procedure. Luckily, residents were very happy to tell us about their gnat experiences once we explained what we were up to.


 Improvised fly-proofing in West Virginia.  Photo: Bill Lamp

Improvised fly-proofing in West Virginia.

Photo: Bill Lamp



Several sites we visited had minimal to no flies. These included the majority of our paved locations, particularly those around Hagerstown and Frederick.  In our experience flies were more abundant in rural and forested areas. Interestingly, the worst flies by far were found in a small forested lot north of Charles Town, West Virginia. Having forgotten our mosquito hats back at the lab, we were forced to be creative with our fly protection that day.




At each sampling site we also measured meteorological variables such as wind speed, temperature, humidity, and light intensity. These measurements will be used for our analysis later this year, as we are interested in both where the flies are and why they are only a problem in certain areas. The flies from our net will also be compared with the flies collected by resident volunteers, to confirm we are finding the same insects that are truly bothering people in the area. We will be out again sampling for adult flies in both July and August. Feel welcome to come say "hi" if you see us in your neighborhood.

Summer 2014 sampling begins

The Lamp Lab is back on the hunt for nuisance black flies during summer, 2014!  Our goal is to refine our range estimate of the black fly problem, and to determine the main larval habitat. Last year, with considerable help from resident volunteers, we collected and identified over 400 flies as Simulium jenningsi, a species whose larvae we found only in the Potomac River and Antietam Creek. This year we will collect adults throughout the season at a number of places, but we need your help to verify that the flies we collect are the same species that are hurting residents. We plan to provide collecting kits to Judy Warner (founder of Washington County Gnat Fighters) for distribution - let us or Judy ( know if you can help with collecting flies. We will also collect larvae from large rivers around the area, particularly the Potomac River. If you see our grad students and technicians swinging insect nets in Washington County, honk!

 Adult Simulium jenningsi collected during the summer of 2013  Photo Credit: Jake Bodart

Adult Simulium jenningsi collected during the summer of 2013

Photo Credit: Jake Bodart

Survey Results

In August, we posted a survey on our website to gauge geographical range and activity levels of black flies in Washington County.  Geographical data can be seen on our map.  The results of our survey indicate that 96% of respondents observed adult black flies at their place of residence.  They were also observed across the county at recreational sites such as Antietam Battlefield, the C&O Canal, and South Mountain State Park.  Peak black fly activity as experience by residents was between May and August, typically during conditions with little to no wind/rain, varying degrees of cloud cover, and temperatures between 70 and 80oF. 

15% of respondents rated black flies a “4” on a scale 1-5, with 1 being not irritating and 5 being very irritating.  The remaining 85% rated black flies a “5.”  Black flies were observed swarming around the face and body and biting, with some participants commenting on severe reactions to bites.  83% respondents stated that black flies had caused them to avoid activities including gardening, picnicking, hiking, walking dogs, and sporting events.  A number of respondents stated that they avoided any outdoor activities because of the presence of black flies.  Some mentioned that they choose to vacation elsewhere or plan on moving away from Maryland because of this annoyance.  

Summer Sampling Summary

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. 

Map of sampling area across Washington County, MD. Inset shows location of Washington County relative to the rest of the state of Maryland. Colored circles indicate locations of sampling points for larvae (red), adults (yellow), and online survey responses (green). Species symbols on the map indicate larvae collected at each stream site.

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.

Sampling the mighty Potomac

This month's sampling trip took us back to a few of the streams sampled early-on this summer, to a couple of new streams, and finally to the great Potomac River. We began our sampling off of Rohrersville Rd, re-sampling some of the streams where we had found black fly larvae earlier this summer. This month however, we found little or no larvae in some of  the streams we sampled, although there were adult flies buzzing around the banks. We did find many other insects besides the black flies we were searching for, including stoneflies, hellgrammites, and one large caterpillar of the imperial moth (Eacles imperialis ). We also found the banks of each of the streams littered with large webs from tetragnathid and micrathena spiders. Presumably these spiders are feasting on any black fly adults that get caught in their webs, but we didn't look closely enough to count whether any were caught.

Imperial moth caterpillar

Photo: Alan Leslie, University of Maryland

Spider web above tributary to the Potomac River

Photo: Alan Leslie, University of Maryland

Black fly larvae on leaf

Photo: Alan Leslie, University of Maryland

However, not all of the streams we visited were devoid of black fly larvae. A small, unnamed tributary running across Bent Willow Rd had several black fly larvae attached to jewelweed plants that had fallen in the stream from the banks. Another unnamed tributary flowing into the Potomac River near Taylor's Landing produced some of the highest densities of black fly larvae we have seen yet from any sampling trips.


Potomac River gauge at Taylor's Landing

Photo: Alan Leslie, University of Maryland

Wading for larvae in the Potomac River near Lock 38

Photo: Alan Leslie, University of Maryland

Submerged aquatic grasses in the Potomac River

Photo: Alan Leslie, University of Maryland

By far the most exciting part of this month's sampling was the chance to look for larvae in the Potomac River, which was finally low enough to allow safe wading from the banks. We sampled the Potomac at two spots, at Taylor's Landing, and at Lock 38, under the bridge leading to Shepherdstown, WV.  At both sites we found a pattern similar to the smaller streams we had visited, where black fly larvae were not attached to rocks that were covered in algae, and instead were found in great abundance on plants growing within the river. These larvae are currently being identified along with the specimens collected from previous sampling trips. We have so far identified at least three different species of larvae from the streams where we have sampled. The next step will be to wait for the completion of adult fly collections and to make comparisons between the distributions of species as larvae within the streams we have sampled, and the identities of adults that have been collected around people's homes. 

Lots of flies in July

 Black fly pupae on grass  Credit: Alan Leslie, University of Maryland

Black fly pupae on grass

Credit: Alan Leslie, University of Maryland

This week we set foot in seven Washington County streams in search of more black fly larvae. This month's sampling trip made a transect from Boonesboro, heading north and west, and checking out all the steams along the way to Williamsport. We stopped once again at Antietam Creek at MD-34, but the other six streams were brand new sites for our sampling project. We were joined this month by two public school teachers who are with our lab this week as a part of a program designed to give secondary education science teachers research experiences during the summer. They both had fun getting hands-on experience identifying and collecting different stream insects. They also had a hands-on experience swatting away some of the adult flies near the streams in Boonesboro.


 Examining leaves for larvae  Credit: Alan Leslie, University of Maryland

Examining leaves for larvae

Credit: Alan Leslie, University of Maryland

 Black fly larva  Credit: Veronica Johnson, University of Maryland

Black fly larva

Credit: Veronica Johnson, University of Maryland

This was the first sampling trip where we came across any streams that did not have any black fly larvae. Some of the streams we sampled had stream bottoms covered in silt, which tends to make substrates unsuitable for larval development. We were also once again unable to sample the Potomac River, as the water level is still much higher than average for this time of the year. Identification of the larvae we have collected so far is proceeding in the lab, so that we will be ready to compare the larval community with the community of adult flies that are currently being collected across the county.

 Discharge graph for Potomac River  Credit: USGS

Discharge graph for Potomac River

Credit: USGS

Expanding our sampling area

 Sampling for larvae.

Sampling for larvae.

Box elder tree in stream.

Grasses along stream.

This past Wednesday, members of the Lamp lab headed out once again to sample for black fly larvae from different streams across Washington County. Because our sampling this month followed storms that brought some heavy rain to the area, we were unable to sample any areas along the Potomac River, but we were able to access six more sites along nearby smaller streams. Within these streams, we once again found many larvae attached mainly to any types of vegetation within the water, as well as a couple of sites where larvae were found attached to rocks. Once water levels drop a bit within the Potomac, we will be able to return to sample several sites along the river.


 Testing the mosquito hat.

Testing the mosquito hat.

We were spared the swarming of too many adult black flies by a relatively constant breeze for most of the day. The heaviest swarms of adults were to be found at the picnic area on MD-67 where we stopped for lunch, and the nearby Israel Creek, where we sampled for larvae. Here, we got the chance to test out some mosquito hats that have been sitting around in our lab for nearly a decade.


Larvae from this sampling trip will be identified to species, and then compared to the species of adult flies that are currently being collected by residents across Washington County, MD. Once the larvae and adults are identified, we should be able to infer which types of streams are acting as the source of the adult flies buzzing around people's homes across the county. As we continue to work on identifying the larvae, we will continue to post updates on the different species that are identified.

 Sampling for larvae.

Sampling for larvae.

Stream sampling has begun

 Sampling for larvae in Antietam Creek

Sampling for larvae in Antietam Creek

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. 

 Black fly adults buzzing around our heads

Black fly adults buzzing around our heads

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.

Collection kits are now available

This week we have assembled kits for Washington Co. residents to use to collect some of the black fly adults that are buzzing around their heads this spring and summer. The kits include five plastic bottles of ethyl alcohol for killing and preserving specimens, as well as labels for recording when and where the adults were collected. Specimens collected with these kits will help with our efforts to identify which species of black flies are causing the nuisance to people, and whether the species change throughout the season. If you would like more information on how to receive one of these kits, contact us through the link above.