Black Fly Season

Black fly season occurs from mid-March to mid-July in Ohio, Pennsylvania, New Jersey, north through New York and New England, the Upper Peninsula of Michigan and into Southern Canada. Some backpackers, campers and fishermen avoid outdoor activities during black fly season, but the rest of us soldier on despite the bugs, glad to escape the confines of snow-bound home life. 

Like mosquitoes, black flies gain nourishment by sucking the blood of other animals. Actually, it's just the females who feed on blood: the males feed mainly on flower nectar. Unlike mosquitoes, black fly eggs are laid in moving water where the larvae attach to rocks using tiny hooks and survive under ice, waiting for the spring thaw. There, they pupate under water feeding on passing organic debris and emerge in a bubble of air as flying adults. When they hatch, they are often preyed upon by fish, such as trout. They live about 4-6 weeks, depending on species, temperature, and food supply.

Black Fly

Black flies are small black or grey insects with short legs and antennae.  Bites can be extremely painful, and their mouthparts are similar to those of a horse fly. Some species of adult black flies prefer humans whereas others target specific animals or birds.  On people, they crawl into sleeves and around boot tops, especially favoring the head just beneath the rim of a hat. Bites can cause swelling and soreness for many days. There are records of both domestic animals and people being killed in a few hours through bites and blood loss. Death can result from suffocation as a result of plugged nasal or bronchial tubes and allergic reactions.

After the black fly finishes feeding, bleeding may continue for some time. At first, the bite site appears as a small, red, central spot surrounded by a reddened, swollen area. Next, the area becomes increasingly itchy, swollen and irritating, sometimes for several days. Partial relief can be found by using anti-itch creams or oral anti-histamines, like benedryl.

Flies usually bite during the day in outdoor shaded or partially-shaded areas. They do not bite indoors or late at night. They are less numerous at higher altitudes due to a lack of breeding sites, cooler temperatures and the the presence of breezes. Black flies are attracted to mammals by the carbon dioxide and moisture in exhaled breath, perspiration and perfumes. They are also 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.

Proper clothing offers good protection against black fly bites. Keep shirt sleeves and front closely fastened and tuck trousers inside socks or high boots. Zippered front shirts will keep flies out better than button shirts. Light colors such as orange, yellow and light blue are less attractive to black flies than dark ones. Shoulder-length head nets are sometimes useful. These can also be impregnated with repellents.

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7 Responses to Black Fly Season

  1. eddie s March 2, 2010 at 10:45 am #

    I wear a full Net Bug Suit, Hooded Top and Bottoms, I bought from Campmor.com a few years ago which solves the hiking with Bugs problem for me. I've worn it while hiking in the Adirondacks in the St. Regis Pond area and in California in the Eastern Sierra's and part of the John Muir Trail during the yearly "hatch" from 10,000 lakes and now down here in south with lots of swamps and streams and wet marshy areas. It also keeps off the Chiggers as well…and you can imprenate it with repellents of your choice….

  2. Mary A. May 30, 2012 at 3:00 pm #

    Just got back from Michigan’s UP, Memorial Day Weekend. The black flys would clump on our jeans and would not leave us alone. Some of them would bite, but the most troublesome was the buzzing and the crawling. I wore a Deet repellant and it did nothing to deter them.

  3. eddie s May 30, 2012 at 3:33 pm #

    Mary was the DEET you were using 100% Deet? I’ve heard, but have no personal proof, that you need 100% Deet whereas a lot of the commerical varieties have as little a 19% Deet…and some of the “Natural” varieties are totally worthless against Black Flies…

    • ben June 22, 2012 at 10:17 am #

      You gain less effectiveness with DEET as the concentrations increase. Reading around some research studies, the French military uses a concentration of 50%. Most scientific studies seem to use a concentration of 30%. The biggest benefit you get form higher concentrations is a longer effectiveness time. Be careful though, many DEET directions at higher concentrations say that you should apply only once a day. I doubt few people follow that direction, but DEET is rapidly absorbed in your skin.

  4. Jason Fellows June 1, 2013 at 10:09 am #

    “Olde timer woodsman” / Fly Dope; sold in the local hardware store in Old Forge, NY, is thee only stuff I have ever found that repels black flies voraciously!! I spend alot of time in the ADK park and live right at the foot hills. It was developed back in like the 1920’s and supplied to loggers in maine by an avid outdoorsman and fisherman; who was also a doctor. It works!

  5. kate henshaw November 17, 2013 at 10:54 am #

    while raking leaves nov. 15th I got bit by black fly, they should have been dead at that time of year. the side of my face, by my ear swelled and itched. I ‘ve been taking an antihistamine orally and it really is helping.

  6. Kathy May 28, 2014 at 8:04 pm #

    Over the weekend black flies attacked my left foot and left hand. Tremendous itching and within 30 minutes my hand and foot swelled 3 x the ice. Packing in ice and Benadryl cream helped. I take chewable Benadryl. It took 3 days for swelling to subside and wear my shoe. Also took honey and cinnamon for inflammation. I am a hiker and outdoor person and this is the first time I have experienced such a reaction

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