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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