Monday, May 20, 2013

Bug Season: Some Tips For Avoiding Black Flies

A-Buckskin-Man-s-Pocket-46Late May and early June is the peak of black fly season in the Adirondacks, and the intensity and aggressiveness of the swarms of these small, dark-colored biting bugs varies greatly from one location to another and from one year to the next. From all indications, this year seems to be one in which there is a definite abundance of black flies in our forests, much to the delight of numerous species of insect eating birds that migrate north to feast on the seasonal abundance of bugs, but much to the dismay of hikers, campers and canoeists that want a wilderness experience free of flying insect vermin.

Black flies, also known as the buffalo gnats, form a group of true flies that are recognized by their small size, dark color, and arched back. Like many other flies placed in this category, the adult black fly depends on nectar and other sweetened fluids for the bulk of its nourishment. Only after the female mates and her eggs become fertilized does she require specific proteins contained in the blood of a mammal or bird. After a single meal of warm blood, these nutrients are absorbed and distributed to her developing eggs.

There are several dozen species of black flies in the Adirondacks, and each prefers to target different hosts at this time of year. Most strongly favor various species of mammals rather than birds, as birds tend to eat black flies. A few species of black flies are known to parasitize only a single type of host, however many investigate any larger, living entity that they detect even though they may opt to refrain from biting after crawling around on the creature’s skin for a brief period of time. Occasionally, a person outside will have numerous black flies buzzing around his/her head without landing, or biting. These individuals are likely black flies looking for a blood meal from another larger mammal, but just not from a human.

Adirondack Black FliesResearchers have discovered that the female black fly initially relies on its eyesight to locate a potential host. Because of this, the black fly is active during the day. Several hours after sunrise and an hour or two before sunset are especially favorable to this small and delicate creature as the air is usually more humid during this period when the sun is close to the horizon. Overcast days and times when a mass of muggy air has settled over the region are other occasions when black flies are active throughout the day. As soon as the air becomes warm and dry, dehydration can seriously impact this small fly. Hiking during the heat of the day when the relative humidity drops to under 30% is the ideal time when black fly season is at its peak.

During dry periods, black flies seek out damp settings, such as dense patches of woodlands where the air is always more humid. They also find a temporary refuge from dehydrating conditions by working their way into the damp leaf litter on the forest floor. This is why disturbing the soil during the day can stir up black flies.

Occasionally, during times of low humidity, some species of black flies temporarily migrate into the damp air that exists just above a quiet pond or lake. Should a canoeist pass through the area, he or she can quickly attract a small cloud of these tiny biting demons. The swarm may be reluctant to follow when the boater reaches shore if the air is too dry.

Like several other biting flies, the black fly also has the ability to “smell” the presence of carbon dioxide in the air. This information helps provide it with the exact location of a warm-blooded creature which produces a plume of this gas as it exhales. Breezy conditions cannot only interfere with the ability of the black fly to accurately maneuver through the air, but also quickly destroy the concentrated cloud of carbon dioxide immediately behind a deer, squirrel, dog or person. During the early morning and later in the afternoon, it is quite common for the wind to die down, which allows the black fly to again use its sense of smell to seek out a source of food.

Places where there is an exceptionally high concentration of carbon dioxide, like downwind from a campfire, can overwhelm the ability of the black fly to accurately locate a host. A fire is often an effective way of eliminating pesky black flies from a campsite, however, care should always be used when maintaining a fire, even in an outdoor fireplace.

There are several ways to deal effectively with black flies for the short period of time they are a nuisance throughout the region, however their presence should never discourage anyone from venturing into the woods at this time of year. It is just like the cold, if you take the proper precautions, you have little to worry about, except if you brought enough to eat.

Above, an illustration from The Book Of Camp-Lore And Woodcraft by Dan Beard; Below, the life cycle of the black fly (courtesy Purdue Entomology, Catherine A. Hill and John F. MacDonald, site authors; and S. Charlesworth, artist).

Related Stories

Tom Kalinowski is an avid outdoor enthusiast who taught field biology and ecology at Saranac Lake High School for 33 years. He has written numerous articles on natural history for Adirondack Life, The Conservationist, and Adirondack Explorer magazines and a weekly nature column for the Lake Placid News. In addition, Tom’s books, An Adirondack Almanac, and his most recent work entitled Adirondack Nature Notes, focuses on various events that occur among the region’s flora and fauna during very specific times of the calendar year. He also spends time photographing wildlife. Tom’s pictures have appeared in various publications across the New York State.

13 Responses

  1. Marco says:

    I believe that blackflies also see further into the deep red spectrum. They are also attracted to heat differences of animals and people and in the ground and air. Example: The bugs coating a fireplace after a campfire the night before. We slammed into a large hatch at Wilmington Notch in 1995, I think it was.

    Permethrin and DEET seem to countroll the majority of them, but, they will penetrate to your scalp or other areas that they can crawl into on your body. Rubber bands around wrists and ankles help.

  2. Brad says:

    Once I see & feel blood dripping down my forehead from my scalp – the bugs have won!

    Sometimes they are just too many, too insistent…no fun at all being outside and the day is ruined.

  3. Annee says:

    Peppermint soap..Dr. Bronners works the best. Wash everyday with it during the dense season. Can use on babies. It kept my kids almost bug free….but when you do get bit..try NOT to scratch..gently take a piece of skin next to the bite and pinch it…those of you who have been bit know:the more you scratch the more you itch.

  4. Barb says:

    Use good old Vapor Rub Yep rub some on forehead neck arms legs exposed areas they hate the camphor smell and stay clear of you …

  5. […] Blackflies have arrived inside the Blue Line—first the slow-moving, mildly annoying but not bloodthirsty males and now the persistent, biting females. With recent heavy precipitation filling the streams from which they emerge and higher temperatures on the way these insects are bound to color Adirondack adventures for the next few weeks. Some folks regard the temporary tattoo of tiny punctures a red badge of courage, and a few outdoor events give the pests their due. […]

  6. Sue says:

    Dark clothing and animals also attract them. Case in point – we have two dogs, one white and one black. The black one is always covered with black flies and not the white dog. I’ve also noticed this when wearing dark clothing as opposed to light colored clothing.

  7. Wally says:

    I’ll never like black flies, but I enjoy learning about them and ways to discourage them. I’ll try the peppermint soap and vapo-rub. Thanks for the article.

  8. Kate Flynn says:

    How about this season, 2014? Is the black fly season late like everything else, or is it almost over…6/30/14?

    • John Warren says:

      Hi Kate,

      My impression is that the worst is behind us, but there is so much local variation that I am always prepared, especially if I plan to be outside in the early evening when they are most active.


  9. Tom Kalinowski says:

    Hi Kate: I am under the impression that our black fly season this year was about a week late, however it was one of the more intense bug seasons that we have had in recent years. I am also laboring under the assumption that the heat that we have experienced these past few days, along with the low humidity, have killed most of the black flies in my neck of the woods. The deer flies are just starting to come out, as are the no-see-ums. This seems to be a banner year for many types of bugs, as I have also seen more fireflies this year than in recent years. Most of these periods tend to be quite brief, and after a few weeks, they are gone. Thanks for reading the Almanack, and good luck with our resident insect populations.

  10. Christine says:

    I am planning a wedding there next May… At Lake George and any thoughts about this would be useful. So far I’ve got campfires, VapoRub, peppermint soap, and of course my wedding dress is white and I will recommend others to wear lighter colors as well. Will inscence work??? Any other thoughts or ideas please feel free to share.Thx. -Chrissy

    • John Warren says:


      Plan the wedding to avoid the early evening hours. Wear light-colored loose fitting clothing and avoid early evening and you’ll be fine.

      John Warren

Wait! Before you go:

Catch up on all your Adirondack
news, delivered weekly to your inbox