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Black Flies

Article posted with the kind permission of the author, Bob Flamm.

Hello folks,

The end of June and early July 2008 hit S.E. Iowa hard with a very above average emergence of black flies.
An area friend who has a large colony called me and told me about all his babies being killed (70-80) by the black flies. I went out and he still had some late nesters and eggs hatching, so he was not totally wiped out, but was hit extremely hard.
The next day I found several dead babies at my colony and the black flies swarming the housing and gourds.
I have compiled some information that I observed and researched in hopes of helping people and the martins. Again: This year was out of the normal and not something likely to happen on such a scale anytime again soon.

Black Fly Info
per: Iowa State University Department of Entomology

We have been receiving a lot of calls regarding black flies over the past week. While we always get a few calls every year, this year the number of calls has been well above average. If I remember correctly, the last time we had a banner year for black flies was about 12 years ago. And, while most people want to blame the increased numbers on the floods and torrential rains we had this spring, that's not the case. To be honest, I'm not sure what has contributed to the problem this year, but it is not uncommon for any insect to go through a cyclic process where some years their numbers may be above average while some years it is well below average.

Here are some facts regarding the life cycle of black flies:

  • Black flies only develop in fresh, running water. They do not develop in standing water sources like mosquitoes. And, black flies prefer to develop in rivers, creeks, and streams that have relatively clean water. Many have suggested that the increase in black fly populations nationwide may be the result of on-going efforts to clean up our rivers, creeks, and streams. Black fly larvae use a sucker-like device to attach themselves to rocks or other solid substrate in the streams. These larvae are filter-feeders that feed on plankton, bacteria, and other organic materials found in the water.
  • Unlike mosquitoes where only the female feeds on blood, in the case of black flies both the male and the female feed on blood. On most animals, including humans, black flies prefer to feed around the facial area. Black flies will also feed around the wrists and ankles of humans.
  • Black flies only produce one generation each year. In Iowa, and most of the country, the adults emerge in mid-June. Since they only produce one generation each year, all of the adults basically emerge at once and can produce large "swarms" overnight. Since it takes them basically a year to go through a life cycle, the adults that are active right now had their start last summer. Therefore, the rains and floods of this spring could not have been the contributing factor in the abundance this summer.
  • Unlike mosquitoes that prefer to feed at dawn and at dusk, black flies prefer to feed in the middle of the day and prefer bright, sunny, warm, and windless days. That is one of the reasons why towns that may be fogging for mosquitoes at night will not notice any benefits in terms of black fly control. The time to be out fogging for black flies would be in the middle of the day when most people are also out and about, which obviously would not be looked on with favor by most of the town's people.
  • The good thing about black flies is that since they only produce one generation each year, the adults will only be present and active for about 2-3 weeks each year. As a result, the black fly numbers here in Iowa should start to decline fairly soon.
  • When black flies feed they inject saliva to prevent blood clotting. Our body's immune system perceives this saliva as a foreign protein and may respond to its presence in a dramatic fashion. Around the eyes, mouth, and ears this saliva may cause some fairly severe localized tissue swelling that may take 7-10 days to subside. While this is not a permanent or serious problem, it can be quite irritating and annoying.
  • Black flies will feed on just about any warm-blooded animal, including birds. On poultry, their feeding is usually concentrated around the waddle and comb. While birds such as purple martins may not be too vulnerable as adults due to limited skin availability, young birds can be aggressively attacked. And, as you have noted, death in birds due to black fly feeding has been documented. This death may be the result of either anemia caused by extreme blood loss or anaphylactic shock caused by an immune response to the large amount of saliva that may have been injected during black fly feeding. Death may also arise from suffocation in ground-raised poultry when birds pile on top of one another in an attempt to avoid black fly feeding.

    It has been my personal experience, and the experience of others, that the standard mosquito repellents containing DEET are not effective or reliable in repelling black flies. To be honest, there aren't any proven and effective commercial black fly repellents on the market. And, while I have heard reports about the success of using vanilla, absorbine Junior, Listerine, and a host of other materials as a black fly repellent, we have no data or experience to either verify or deny these claims.

    You indicated that one individual had recommended spraying the housing with pyrethrin and DEET. As I just mentioned, DEET doesn't work well as a black fly repellent. And, while pyrethrin also has some repellent properties as well as being an insecticide, any benefits from its use would be extremely short-term. In fact, pyrethrin has such low residual activity that it is usually recommended to be used on a daily basis. I wish I had a better recommendation for you, but to be honest, I don't. Using a pyrethroid insecticide such as those that contain the active ingredient permethrin, may provide slightly longer residual protection than using a pyrethrin spray. But again, there are no guarantees.

    While their numbers are significantly higher this year, this does not mean that they will also be high, or higher, next year. A lot will depend on whether the rivers, creeks, and streams that are serving as the source of the black flies continue to flow clean and free the remainder of this summer, this fall, this winter, and next spring.

    My own personal observations at my colony and some further research.

    I wanted to compile some of my notes to let you all know what I saw and some of my personal conclusions.

    I have already posted the black fly info above on their breeding cycle and how they laid their eggs the previous year and emerge in streams the following year as adult flies and take to flight. Other research I’ve done on black flies:

  • “Black flies are strongly influenced by color -- they find dark hues more attractive than pale ones, and blue, purple, brown, and black more attractive than white or yellow. A light-colored shirt, therefore, is a much better choice of clothing than a dark blue one. It is a moot point, however, whether blue jeans might not be better than pale trousers: if they are carefully tucked in at the ankles and are without holes, jeans may help to attract the flies away from the head region.” Courtesy Rocco Moschetti, IPM of Alaska.

  • "Black flies often swarm around a person's head because they are attracted to carbon dioxide in the breath (CO2). Bites are concentrated on exposed areas of skin, especially along the hairline, feet, ankles and arms." Courtesy Jeffrey Hahn, University of Minnesota Extension Service.

  • "Bug Off" National Wildlife June/July 2002, Vol. 40 Issue 4, p. 9.; Reports the use of organic materials as insect repellents, including a comparison of aromatic oil from catnip with the chemical used in most insect sprays; the need of testing the safety of the oil; and consideration of the potential use of black pepper.

    My conclusions after finding this info and looking back:

    1. The black flies went to my housing first. My trio2 house is totally dark blue, my ramp trio has dark purple porches and trim. The red barn, the end rooms where the sides are red was hit early. They hung around my bo gourds under my barn a lot…red tunnels. All the dark colored areas on all 3 houses were 1st hit.

    2. They went after oldest babies first. There is more CO2 from their breaths in those rooms and gourds because they were larger clutches from older birds. And they are typically sticking their heads out begging for food. An easy find for the black flies attracted to CO2. Un-vented gourds were hit harder than gourds with vents. Possibly allowing the CO2 to escape and not build up in rooms and rush out the entrance. Could be why they hung around entrances so much of the un-vented gourds and rooms. I put orange slices by some entrances, which made many go away from that area, possibly just masking the CO2. On days of just slight winds, they would congregate on down wind sides, CO2 being pushed to the down wind sides?

    3. Tim (friends colony west me 7 miles who lost many babies to them), put wild catnip clippings in his rooms with babies that were just hatching. Those babies fledged. Did it repel them or just mask the C02? He later took liquid garlic capsules and smashed them on his fingers rubbing a line of the garlic oil down the babies back. He also said his wife had problems with bugs in their peach tree before. She bought garlic bulbs and cut them up and hung the pieces in silk bags on branches around the tree. It kept the bugs off all summer. I can not confirm any of this as to its effectiveness because I haven't tried it.

    4. Nests that were extremely dirty with feces got a lot of attention. Nest changes helped in those situations. After visiting tim’s colony again, I tried cut up garlic chunks in panty hose bags hanging and wrapped around a couple gourds the black flies were congregating around that had babies inside. It did nothing for repelling the black flies. Tim’s success must have come from putting it right on them. This was feasible since he only had a couple nests left with babies. Too much work with all my babies to go to that extent. I went back to the pure vanilla mist, I knew it worked. I am interested in the vanilla oil for extending its length of effectiveness and will try that next year with follow up research.

    In summary: The darkest of colors seemed to get their attention and then they hung out at entrances of cavities with babies inside. They hung around the entrances of un-vented gourds more than the ones that were vented. They hung out at stinky cavities also. Cavities with older babies sticking their heads out got hit quickly.

    My findings also found the pure vanilla extract worked just as good as the pyrethrin spray at repelling them, both last 6-8 hours. They need reapplied twice a day to be fully effective. The advantages of pure vanilla are obvious; it is just as effective, it’s natural and non-pesticide, easily applied with a mist bottle, didn’t have to cover entrances and didn’t have to mess with the babies. A vanilla essential oil may last longer yet?

    Nest changes helped in lowering odor output of dirty cavities.

    Rooms with sevin dust did nothing to repel them.

    I tried DEET and it did nothing to repel the black flies.

    Tim’s experimentation with garlic and catnip is promising also.

    The trick in saving them seems to be in catching it quickly and keeping the masses off them for repeated days. If they get hit by too many at once, they are done. And it doesn't drag out, they are done quickly! If you do ever get hit by what we did here; you will lose some, but you can save many very easily also.

    Just being bitten does not kill them…too many at once or repeatedly bitten will. By the time I was doing a second treatment within a day or on one’s that I didn’t treat or used something that didn’t work; I saw numerous black flies that had blood meals sitting on gourd arms, house railings, walls, porches, and on babies themselves. Yet well over a hundred fledged.

    The sun, heat and wind all had effects as to how long the effectiveness as a repellent anything worked that I tried.

    I also noticed during this that extremely dirty nest are an attraction to them also, probably just smell.

    I have found two products since all this that is used with traps you can buy and hang with some very pungent smelling mixtures that you put in them. And they last for several days they say. Might work well for hanging around housing and gourds in extreme cases? They are advertised as a non-pesticide.

    And they are advertised to work for blow flies!
    Something to try in the future...Farnam and Rescue. Various types of traps and one says it draws them in from 250 square feet. Definitely something to try.


    Now why this year? If you look back at reported years of higher populations of black flies you will see most, if not all, were during June and July with higher than normal rainfall amounts. But we now know these black flies laid eggs the previous year.

    My conclusion: The spring rains turn these clean clear streams rampant and dirty, sometimes going over the banks and spreading them out even more. We had mass flooding this year in the Midwest. Any trout fly fisherman knows the best time to go fly fishing is when the mayflies are emerging from the streams. It puts fish in feeding mode to feed on these emerging flies. With excessive rainfall during these emergence times, the water turns rampant and dirty. The minnows and smaller fish that typically would get some of the black flies as they emerge could not see them in this altered water. Thus the black flies emerged and all made it to flight.

    I hope this helps some of you in times of high population outbreaks. Quick action is the key. Some things I will remember, June is the month they emerge, how much rainfall we have had (what are the streams like).

    My remedy to combat these of just misting the outsides and entrance areas with vanilla worked very well for me. It takes 10 minutes to do all 4 of my poles. I don’t need to cover the entrances or mess with the babies… I did do some nest changes on really dirty nest, but not that many. That seemed to help in keeping down other scents that may have possibly attracted them also.

    This year was very out of the normal and isn't likely to become a major trend. I was sad for the martins and landlords who lost babies to these black flies. I don't know if this would make the adults leave a colony to never come back though either. I could tell by watching them that they knew it was the black flies.

    With quick action, having local friends that keep each other informed and nest checks, I lost just over 30 babies. That seems high, but considering some colonies lost all their babies, I feel I did well. I could have saved even more, but time is a consideration also. And I had to do it controlled, which meant misting some and not other cavities. But I beat it with help from others and the vanilla, real vanilla, not imitation, and have been fledging babies the last few days and have 70+ still alive. In total...I still fledged well over 100 babies!

    Finally...the purple martin has become very dependant on us to provide housing for them. Pay attention to them. In cases like this…timing is the key.

    Article Courtesy of Bob Flamm- Purple Martin Research Group (2008)

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