Black Flies
From mid-May to mid-June, Black flies swarm over the North East. Like the Mosquito, it is the female that bites, but the males that swarm around the females increase the nuisance factor. On the worst days, the swarming can drive a person insane, making it impossible to remain outdoors. At other times it is only miserable. The biting females find any exposed skin, crawl through openings in clothes to get at skin and crawl into ears and the nose. Fortunately their season is relatively short, only four or five weeks.

The female bites a hole in the skin to suck the out blood. This bite is not painful and often is unnoticed by the victim. That is because a combination of chemicals is injected, including painkillers, toxins and anticoagulants. In response to these chemicals, the area around bites swell, become painful and itchy. Black flies do not transmit any diseases to humans, but some people have an allergic reaction to the anticoagulant including fever, nausea, and rashes. I was bitten so much one day that I felt nauseous for about three days.

Black Flies don't like wind and are only active during the day. They prefer shade. They breed in fast flowing rivers so avoid climbing near these in Black Fly season. However they can range more than five miles in their search for blood. To protect yourself from black flies, cover yourself in light-coloured clothing since they are attracted to the darker colours. Repellents offer some relief but at times the flies bite no matter what repellant that you use. 

Bites can be treated with soothing lotions as well as corticosteroids to relieve pain and itching and help lesions resolve. If the reaction is mild, oral antihistamine therapy may suffice, but severe reactions involving shock may require epinephrine (consult a physician). I have never needed anything to treat the bites, I just try to keep the wounds clean to avoid infection.

In Ontario, Black Flies are prolific in most areas. However, I have never seen many on the Bruce Peninsula. The few that I see in the forest are not a problem. On the Peninsula, it is often windy and there are almost no fast flowing rivers. Whatever the reason, this is the place to climb in Black Fly season.

Bob Bennell
Oct 2001