Q. What can I do about black flies? I can't do any gardening or stay outside because of them, as I am highly allergic to their bites. I would like to be able to tend my flower garden but cannot. And the state, county and town refuse to spray.
- ---Marcia; Down east Maine
- ---Martin in Yardley, Pa
I'm thinking these pests are what I've always called black gnats, as they're very small, and are also known as 'turkey gnats' (because they attack and then infect domestic fowl with nasty illnesses) and 'buffalo gnats' (because they have that kind of curvy humpy back thing going on).
Don't blame the cherries and berries for the flies. If anything, 'blame' the flies for more fruit being out there! Black flies don't feed on fruit, just the flowers that precede it, as both males and females consume pollen and nectar for energy. And in doing so, these pests help to pollinate the plants and thus potentially produce more fruit for you. (They may be important pollinators of blueberries, as the flowering of that tasty crop often coincides with black fly population peaks.)
As with most pestiferous insect species, it's only the females that cause pain, as they need blood meals to raise their young. Like we humans, the males are harmless, gentle creatures. Ahem. Actually, not all female black flies suck blood, but the ones that don't swarm around your face in such numbers it almost doesn't matter.
They are in the same family as mosquitoes, but black flies breed in streams and other moving water, instead of the stagnant stuff that baby mosquitoes prefer. After draining your hemoglobin reserves, the females lay their eggs in or near that running water. Weird little underwater larvae hatch out and feed on muck and plant material, emerging as winged adults when the water reaches a certain temperature the following Spring. Trout love this event, but there never seem to be enough fish to make much of a dent in the pest's numbers.
As with mosquitoes, they're probably too small for bats to bother with (bats tend to eat bigger bugs, like moths). But birds are a good idea; try to specifically attract swallows and other known mosquito eaters with the right kinds of nesting boxes and birdhouses.
"Spraying" by the authorities won't help, but Bt can—specifically BTI. The same strain of this organic pest controller that prevents mosquito larvae from developing into biting adults also works against black flies. Application is trickier because their water is moving, but Pennsylvania has developed a successful program in which rivers are treated at just the right time to reduce their numbers significantly. If you have a moving body of water nearby, try suspending some dunks or packets of BTI in the water beginning a month or so before typical blackfly emergence time. (Gardens Alive sells packets of BTI under the "No-Squito" brand. Hey GA--who comes up with these wacky names???)
Unfortunately, these little monsters are not homebodies like mosquitoes, and often fly (or are blown) miles away from their watery birthplace. So I would definitely give the Mosquito Magnet (or similar propane-powered carbon-dioxide trap) a backyard try. When I got a Magnet to test, I had to empty blackflies out of the collection net every day. The manufacturer later confirmed that these machines seem to excel at catching 'biting gnats'.
Black flies are also attracted to dark colors, so one tactic is to wear only light-colored clothing. Another is to wear light colored clothing above the belt and long jeans below, as the suckers may keep trying to get at you through the dark denim and leave your poor head alone. DEET is toxic and should be avoided at all costs, AND there are reports that repellents containing DEET actually attract these pests, as they do ticks.
That leaves permethrin clothing sprays and natural repellents that have been shown to repel skeeters in medical studies, like Bite Blocker (which Gardens Alive sells as "Sting Free") and Repel Lemon Eucalyptus. (Catnip has also been shown to work well, but I haven't seen any studies of actual products containing it.)
So try a verified non-DEET repellent during black fly season or treat your clothing with a .5% permethrin spray. These sprays contain a very low concentration of an artificial analog of the old botanical insecticide pyrethum, and you only spray them on your clothes, not your skin, so they're "allowed" in my otherwise kosher organic arsenal. Spraying your clothing keeps you free of mosquitoes and ticks, as well as biting gnats and flies.
This leaves your face and head, perhaps the most important body parts you need to protect (because that's where the pests swarm, not the reason you thought of). If I lived in black fly land, I would probably wear an insect veil outdoors during Biblical Times. (You know, like beekeepers use when they have to take apart a hive.)
You can also reportedly trap them on a sticky hat, using double-stick tape or those highly-effective deer fly patches. Just be sure to try this tactic with a veil or your face treated with a safe, non-DEET repellent. Without face protection, a trap-in-a-hat would provide more revenge and personal satisfaction than actual protection.