Black Fly Program

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.

Life History of the Black Fly

There are four stages to the black fly’s life, and three of those stages are spent in fast running fresh water. Vectrobac ONLY targets the larva stage of the black fly’s life cycle.

The first of these four stages is the EGG. The female lays her eggs on the grasses or in the mud along the edge of the stream, or sometimes she will lay them right in the water. Depending on the species, these eggs may hatch within a few days, or may lie dormant until the next year.

The second stage is the larva, (plural; larvae). It is a small worm like creature which can be found clinging to rocks, grasses or debris in the water. The larvae attach themselves to any fixed object in the water, and let the water bring their food to them. The larvae have two extendible head fans which are used to capture food particles carried by the current. These fans close and are swept clean of these particles in a fraction of a second by the insects jaw. The jaws then push the particles into the mouth. The rate of feeding depends on the amount of food in the water, temperature, and the speed of the water. Most black fly larvae are filter feeders. They can be found in flowing sections of the streams, and many species in fast moving water only. Black fly larvae have the capability to move or swim up or down-stream. A disruption in their normal environment or lack of food can cause them to relocate to a different part of the stream.

The larvae have from 6 to 9 instars depending on the species. An instar is basically a step in the larvae growth. The insect can only grow so big and then it has to grow a new skin. An instar is the term for each larval stage or, the growth of a new skin, and the shedding of the old one. The third stage of the black flies life is the pupa, and during the last few larval instars, the insect starts to take on the pupal characteristics. By the end of the last instar, they are a pupa, in the larval skin. Then they usually move out of the direct current of the water, into a crack, or behind a stone, branch, or into vegetation. Then they spin a cocoon which is open at the head end, exposing the head and thorax.

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