Black Fly Info

Black flies really are a nuisance but I hope you won’t let that keep you inside.  There are repellents and gear that work well to protect you from being bitten.  Get out and enjoy Maine nature – even the black flies.  You can tell everyone you’ve experienced the black flies and lived to tell about it!

Black flies bring more readers to Maine Nature News than anything else.  It isn’t the moose, foliage, loons, hiking, river rafting or even a combination of all of these – it’s the black flies. Dress appropriately, use a little spray and have fun!

I speak with the media each spring about black flies. If you’re a writer/reporter you’re welcome to email me.

Gene Thompson
Editor, Maine Nature News

When is “Black Fly Season”?
There is actually no single, uniform “black fly season.” The maps in the Maine Nature News archive are based on scattered local observations. But, there is enough information there to draw some tentative general conclusions for some locations in Maine.
Do the black flies persist after July? What is the best time to camp and hike in Maine and avoid the flies?
Black fly larvae, which hatch in clear running streams, do not hatch until everything thaws and the water temperature has also risen a bit. The black fly season moves, in general, from South to North and simultaneously from the coastal plain to inland areas and from lowest elevations up to the highest. So there is no precise “end” to black fly season in Maine. However by mid-July in most places after the birds have start gobbling them up, and after the black fly adults have bred for the season and go into “dormancy”, the numbers dwindle drastically almost everywhere. During wet summers like 2009, the black flies can still be prevalent in late summer.

Here are some more key pieces of information, as a further general answer to your question:

  • Black flies breed in running water, unlike mosquitoes, which breed in still water. Because there are about forty species, not all flourish at the same time.
    Black flies can travel several miles from their breeding site, so those environmental rules cannot be counted on completely, as a means to avoid them.
  • Strong breezes tend to disperse them, as they are a very small insect.
    I have found, and others confirm, that black flies are generally inactive until the air temperature has risen to at least 50 degrees F., even in black fly season.
    I have also found that they seem less numerous at higher altitudes, probably because of a combination of the above three factors: the lack of expansive breeding sites, cooler temperatures and the more consistent presence of breezes.
  • “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. … Bites are concentrated on exposed areas of skin, especially along the hairline, feet, ankles and arms.” Courtesy Jeffrey Hahn, University of Minnesota Extension Service.
  • “The bites can produce a variety of reactions ranging from little or no irritation to considerable irritation and swelling. Sensitivity varies from person to person.” Courtesy Jeffrey Hahn, University of Minnesota Extension Service.
  • In general, unlike mosquitoes, they will not fly at night or penetrate most clothing.
  • Local variation is the rule. Local people are usually the most helpful resource, as they observe these things very carefully.
  • Head nets and body nets really work, if one takes care to leave no gaps where the netting meets the shoulders or the ankles. Head nets can be draped over the hat you usually wear, or a version with an internally attached cap can be purchased.  When used without a cap, care must be taken to leave a small space all around the head that the insect cannot penetrate.

I am interested in the Latin name of the Maine black fly.

The black flies comprise the family Simuliidae, and that is probably the best collective Latin name to give for them as a group.  Many (but not all) are in the genus Simulium.  Around 40 species are common in Maine, with about 10 – 15 species flourishing at any one location during the course of the black fly season. I would hesitate to name any one species as the “most common,” but Simulium venustum and Simulium vittatum  are found almost everywhere in the state, in varying numbers.

My wife calls a black fly a “MayFly.” I always thought a mayfly was a long flying insect with a waggly tail … that comes out in May.   The black fly comes out as early as April so I can’t understand why she thinks it is a May fly. Could you help provide the answer as to whether or not a Black Fly is a May Fly?

Black flies are generally 1/6″ or less. There are many species in North America. They all breed in running water. The females bite to get a meal of blood. They are a nuisance to humans in Northern areas from approximately May through July. Adults may live several weeks. All are members of the family Simuliidae. A nickname for them is “buffalo gnats.”  I have not heard of them being called mayflies.

American mayflies range from 1/2″ to about 1-1/2″. There are about 550 species in North America. They breed in lakes, ponds, streams. They spend most of their lives in water as nymphs, a non-flying stage in their development. The adults emerge winged from April through October. They do not feed at all during their brief adulthood, and die after 1 or 2 days. All are members of order Ephemeroptera. I do not know of any nicknames for mayflies.

Unlike mosquitoes, black flies seldom attack indoors or even in in a vehicle; once they sense being trapped their attention seems permanently diverted to escape and they spend the rest of their lives crawling up the screen or window pane.”

Black flies breed in running water, unlike mosquitoes, which breed in stagnant water. Although there are some studies about black fly larva control, there are logistical and environmental concerns:

a)   Most public water supplies originate in streams and other running water bodies.
b)   Larvae locate in very localized clusters, in dispersed, inconspicuous locations, making pesticide application much less cost effective than for other insects.

Black fly appearance is characterized by a succession of flourishing of as many as 20 or 30 species in a locality, each with their own breeding time and cycle (some twice a season) complicating the management of any attempted control measures.

* The Maine Agricultural and Forest Experiment Station has five publications you might want to know about, and perhaps obtain via interlibrary loan through your library:

  • Black flies in Maine: biology, damage and control. 1977. (Maine Agricultural Experiment Station Miscellaneous Report No. 188.
  • The Black Flies of Maine. 1979. (Maine Agricultural Experiment Station Technical Bulletin No. 95)
  • Experimental Stream Applications of B.T.I. for Human Nuisance Black Fly Management in a recreational area. 1988. (Maine Agricultural Experiment Station Technical Bulletin No. 133
  • Possible control of the Black Fly Simulium Penobscotensis by Temporary Habitat Alteration. 1979. (Maine Agricultural Experiment Station Miscellaneous Report No. 215.)
  • Research on the Black Fly Problem in Maine, a Report to the 105th Maine Legislature. 1971. (Maine Agricultural Experiment Station Miscellaneous Report No. 131.)

Most control has concentrated on personal measures, such as use of repellent, and timing activities to avoid the hours, dates, temperatures, or places of maximum appearance.

Could you please clear up a question that has been the subject of much discussion around our campfires? Does the Black fly pollinate the Blueberry?

Three important things pertain to answering your question.

1. As you may know, the black flies we see at any given time may actually be of different species, each with its own habitat and hatching time — at some times more than one species is prevalent in a locality at one time. A few species hatch more than one generation in a year. Only the females of the various black fly species feed on blood, and not all feed on humans. (Some swarm only, but without biting. Others are not attracted to humans at all.)
2. According to Jeffrey Grannet’s Black Flies in Maine; biology, damage and control (Maine Agricultural Experiment Station Misc. Report 188. 1977): “Male black flies do not bite. Their only source of nutrition is plant nectar or sap.”
3. A lot of the plant pollination in Maine is done by species other than honey bees, since these do not easily survive the Northern winters. (Wild bee species, wasps and even hummingbirds all contribute.) By deduction, since there are adult black flies present almost all during the non-winter months, and since some feed on plant nectar thus incidentally pollinating as they feed, and since blueberries are in flower during months when black flies are present, I would conclude that, yes, some pollination of blueberries (and other flowers) may occur by some of the black flies.

The following would seem to strengthen the case. Roger W. Crosskey The Natural History of Blackflies (Chichester, UK: John Wiley & Sons, 1990) notes in the subchapter on “Feeding on Plants”, subsection on “Attraction to Flowers,”:

“Probably almost any flowering plant will at times attract some blackflies in its flowering season if it is nectar productive, even if certain species have favourite plants in different parts of their geographical range. … in Canada, the blueberry plants Vaccinium angustifolium and Vaccinium myrtilloides are specially attractive.”
(Note:  I believe the common wild blueberry in Maine is Vaccinium angustifolium, although there are several other species.).

More grist for the campfire stories, I guess!

Why are they called black flies when bigger houseflies are also ‘black’?

Almost every animal and plant has a scientific name and a common name or names. The scientific name is universally used by scientists and students worldwide.  The common names are used in daily life and may vary from one place to another for the same animal or plant.  The group of true flies includes: house flies, deer flies, horse flies, black flies and many other species.  The scientific name that the insect family of all black flies share is Simuliidae.  However this insect has many common names such as:  black fly, blackfly, buffalo gnat, and reed smut.  In French-speaking Canada they are known as mouches noires, in Latin America as jejenes, and so forth.

To the European explorers who first came to the Western Hemisphere black flies were almost unknown in their home countries. When they encountered them here they gave them various names, usually by comparing with insects already known.  According to Roger W. Crosskey’s book The Natural History of Blackflies (Chichester, UK: John Wiley & Sons, 1990) the name was first used in New England, by at least the late 1700’s.  The earliest non-Native persons to encounter them were merely describing the “new” insects in terms of the known insect group “flies” and the fact that they are dark-colored and that they are a type of fly.   Thus the name “black fly” came into common use, as there was no commonly used alternative.

Q1:  Our son is real sensitive to any bug or mosquito bites.  What is the best form of prevention and the best form of relief post bite?
Q2:  I was hiking on a trail and something bit me behind my left ear although I didn’t know it at the time. About three days later I had a sore throat and earache on the left side of my head and pain to-the-touch in the same general area up to the top of my head, as well as, about six bites and swelling behind my ear. I didn’t suspect Black flies because there was none of the usual sensitivity, itching or welts common with the bites. I ended up going to the doctor. All is well now except for some slight stiffness and pain that seems to be receding quite rapidly each day.
Q3:  When a human is bitten, and as I have seen the swelling and itching, is there potential for an infection specific to this gnat and to what degree does it occur? We recently spent a weekend at our house and of course she has sustained a bite on her head where her hair meets her forehead. There is an intense red circle about the size of a quarter at this site and a more diffuse swelling about 3 inches which is not discolored that extends across her forehead from hairline to eyes, with resulting headaches and eye sensitivity.

From time to time people write in to the Maine Nature News with questions similar to the above.  Many people spend time outdoors with no ill effects from biting insects.  But under some conditions, and with some individuals there can be unexpected reactions.

Generally black fly bites cause some itching and minor swelling from the first few bites of the season, following which an immunity develops, with subsequent reduced reactions.  Nonetheless, even individuals who have lived all their lives in black fly country and are exposed every season, can have greater effects if they get an unusually high number of bites on their first exposure of the season, or have some significant change in their physical condition or medical status. Therefore everyone should take this possibility into account as they do with all other outdoor risks, and take appropriate precautions.

Please keep the following things in mind:
1. Learn about the insects in the areas you visit. Your local library can help you.  Also, some links to informational web sites are listed below.
2. If you already know you have some sensitivities or allergies then you should talk to your doctor ahead of time and plan to take precautions when recreating in the outdoors, especially when you visit an unfamiliar location.
3. If you get a bite or sting make a positive identification of the insect or arachnid from which you received it.  Not all alleged black fly bites are really from black flies.  Get positive professional identification.4. Get medical attention for any reaction that appears unusual or concerns you.  Be sure to let the doctor know positively what bit or stung you.