Facts About the Black Fly

Black flies are those tiny, black, or dark brown flies, that look like baby house flies, they bite you, and make your summers miserable! The adult black fly is between 2 to 5 mm in size and their legs are much shorter than those of the mosquito.

The adult black flies will emerge from the streams in late April, mate, and without obtaining a blood meal, will lay their first batch of eggs. They will mate again and not be noticed as a pest until late May or early June when they go in search of a blood meal to develop their second batch of eggs.

Both Males and females feed on nectar from flowers to provide energy for flight and survival. Only the female black fly bites, because she needs a blood meal in order to develop her eggs. She has special mouth parts which slice the skin and feeds from the pool of blood.

If females develop their first batch of eggs on larval reserves, and then take a blood meal for their second batch, the biting problem will occur several days to weeks after the adults have hatched. Therefore these species must be treated for control several weeks prior to the first evidence of biting.

Some early biting species have larva that hatch in the late fall, and over winter in the streams and rivers. Running water never reaches less than 4 degrees Celsius, but in the spring, when the water goes above that temperature, the larva will develop faster and pupate. Knowing this, you should be prepared to make your first treatment by mid April.

Just to give you an idea on how many black flies can be produced in a small area, it is quite possible to have 10,000 larvae per square metre. If you are living next to a stream that is 1 meter wide, there can be 500,000 black flies produced in a 50 meter section of that stream. That’s half a million black flies!

Some people argue that by removing the larva from the streams you are taking food from the fish and other creatures in the stream. Studies show that black fly larvae are only a small part of the fish diet. Fish are opportunistic creatures, and will eat whatever food is available in the stream. Also, with proper monitoring, you will only be treating when and where necessary in the stream.

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