Black Fly Facts

First, a black fly’s life span is about three weeks, and it’s the female that does the biting.
The next question that gets asked, how come we can have the pesky devils around from mid May to the end of June and even into July? It all depends on the weather and how fast the spring run-off creeks and small rivers dry up.
One myth has it that as soon as dragonflies are in the air, usually a week or two later than the black flies, they then eat all the black flies, thus putting an end to these annoying creatures. While it’s true that dragonflies gorge themselves on black flies plus other flying insects, they are not the cause of the black flies’ demise. Another is when the buds of all the trees finally burst open or when the trilliums fade away that’s the end of the black flies. Not so.
There are many species of black flies (165 in Canada) but only two that swarm and annoy and bite us Ontarian’s.
They are both similar, although breeding habits differ slightly. Their life cycle starts when the female lays some 150 to 600 eggs on vegetation or other substrates such as rocks or stumps or simply scattered over the water’s surface of streams or creeks. And always on bodies of water that are moving, unlike mosquitoes who thrive on stagnant waters. And interestingly enough, only waters that are uncontaminated and free of any kind of organic pollution. Since the waters in Muskoka / Lake Bays are clean running, we in turn get an abundance of black flies.

The name black fly is also a misnomer as world-wide there are some 1,800 varieties and of different colours, although for the most part, the flies that are biting you are black in colour. The eggs then hatch into larvae as they attach themselves to anything that’s convenient and underwater. Then over the next months and through the winter, they eat algae and small organic particles that pass by them in the running water.

The larvae then develop into the pupae stage and, as time goes on and the water temps warm up, 5 to 10 degrees (40 to 50 F.) they develop into adults where they will float upwards in a bubble of air and are ready to fly as soon as they reach the surface.

Adults mate almost immediately and while the male then goes off looking for some kind of nectar to drink in as nourishment, the female goes hunting for blood as she needs this so she can lay her eggs. They find their blood meal by the scent of carbon dioxide and body heat, mostly from animals, birds and, if they get real lucky, from the flesh of some hapless human. Dark moving objects will catch their attention, the same for humans wearing dark clothing. Lactic acid as produced by a victim’s skin will also attract the thirsty females A bonus to these flies, is when humans douse themselves with soaps, lotions, aftershave, perfumes and hair products. For the fly, it’s like a bear to honey.
Once she has fed and digested her blood meal, she will lay her eggs, usually back into the same stream or creek where she emerged from.

Unlike mosquitoes who leave their barb in your skin, thus inviting disease, the black fly simply takes a chunk of your skin, which means the flies we experience that are north of the Severn, pose little health risk to humans.
As the water temps warm up, not all of the pupae have developed to the stage of emergence. As time ticks on and the waters keep running, more will emerge in drips and drabs till finally they all have hatched or the waters dry up, killing off whatever pupae didn’t make it to the emerging state.

What speeds this whole process up is if there is several late May to early June days of hot weather to dry up the streams and creeks that they live in. And then they are gone until next year. But if we have an ultra cool spring, they may still be biting on into July.

Some facts
• A black fly’s life span is about three weeks
• They emerge mid May and die off after the spring creek run-off has ended
• Wear light coloured, high neck, long sleeve and pants with the rubber bands at the end of the arms and the leg end tucked into socks.
• For the flies that swarm, a protective head net should be used.
• They are most active in the morning, late afternoon and on warm, overcast days.
• Black flies are most bothersome in the bush rather than open country.

Two products that have been given excellent reviews and do not use DEET are
*Repel Lemon Eucalyptus Insect Repellent Pump Spray
*Sawyer’s Fisherman’s Formula Picaridin Insect-Repellent
Content taken from an article written by David Foote

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