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The return of the black fly

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This pest of the northern spring can travel up to twenty miles on the wind. How to get away? Dress in yellow, some suggest, or tie a dragonfly to your hat. Martha Foley and Dr. Curt Stager consult.

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Martha Foley: Once again it is black fly season. People who don’t know black flies are always abhorred and annoyed about these flies. It's true, I suppose there are places around the world that don’t have black flies, but they’re such a fact of life.

Curt Stager: Yeah, it’s a really active field of research partly because of the nuisance factor. It's got economic impact in places like the Adirondacks or northern parts of North America because it's so miserable at certain times of the year.

MF: You hear about Alaska being the kingdom of black flies.

CS: And of course parts of the world you catch diseases from them, too, so it's an active field of research but just imagine how hard it would be to figure out what these things do partly because they go after you if you’re trying to study them. They’re so small and it's really impressive.

MF: And there is so many of them!

CS: I try to track down scientific papers about how people do some of these things. The most obvious way, I guess, you could study abundances of black flies is just tie someone out in the woods and count how many bites they get in a minute. There are technical terms like MBR and ABR which is monthly or annual biting rates.

MF: Do you they actually do that -- just stick your arm out a window?

CS: There are actual studies where they put a person outside and count how many times they got bitten. There was a study in India and they wanted to see what colors of clothing attracted black flies that bite people. They put out men in different color suits to see which ones would get the most bites. Usually it's black or red suits had a lot more bites than the ones in the green or the white suits, and the yellow suits had the least. We have different species here I’m sure but you might want to try dressing in different colors and see if that helps.

MF: I take my dog with me and make him lay down about 15 feet away so he can attract the black flies.

CS: Other things that people go through to study these, like you'd want to know how far do they travel, for instance, and if they do, how does this fit into their life cycle. That’s important because if you do eradicate them in a certain area, like with the streams dropping bacteria, you want to know how they re-colonize and where do they come from.

MF: If you could do that once maybe they wouldn’t come back, if you knew how they moved.

CS: Just to control them better, maybe if you spray them here but they’re actually coming in from somewhere else. One obvious way to try is to mark and recapture them and see where they go but that’s really tough. People sometimes try with paint or colored dye or dust but it's hard to get the stuff to stick to them

MF: Because these are little tiny bugs.

CS: Yeah it kills them. One researcher succeeded in the 1970s in West Africa. He actually marked some and found them 20 kilometers away after about a day or so, and that basically meant they had to be carried on the wind.

MF: That’s kind of discouraging for people who want to eradicate black flies in their town. They could just blow over from the next town the next day.

CS: Some of them go 50 miles that way in the wind. One way it was studied was actually not with individuals but wiping out a whole area with a pesticide of some sort, I guess it doesn't matter what kind, and then you check the surroundings within 50 or 100 miles and see if you get a population decline at the same time downwind of that place, and sure enough, people find that about 40-50 miles away these things fly up high into the air where the winds can catch them and blow them downwind and that probably disperses them.

MF: Is it really true that the best way, if you have to be outside and you don’t want to be bothered by black flies, is it true that if you tether a dragonfly to your hat it will scare them away.

I hear it is and actually male black flies often will swarm together hoping females show up and they will disperse if a dragonfly shows up. I guess they don’t see all that well so they can hear them coming so in theory that would work.

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