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Jump down to: [Midges]  Black FliesBlack flies (Simulium sp.) are present in the San Gabriel Valley. In tropical Africa and northern Latin America, black flies are vectors of the filarial worm that causes the disease "river blindness". Locally, black flies do not transmit disease but can cause extreme discomfort and irritation due to their biting habits and/or great numbers. They often appear in large numbers, flying into the eyes, ears, and nose of anyone nearby. The females of two of our three species will bite people or other mammals to acquire a blood meal necessary for egg development.
Black flies breed in flowing water, from rivers and streams to irrigation ditches and accidental seepages. They can be found from spring through fall with the greatest numbers appearing in the late spring, and throughout the summer.
In our area, control measures are only necessary in extreme cases when numbers of adult insects are high. This insect also breeds in flowing waters, and tends to prefer the shallow, nutrient rich waters found in the storm drain systems in our area.
As they are physiologically and genetically very similar to mosquitoes,
the larvicidal agents used for mosquito control (insect growth regulators)
also work well to control midge populations.
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Control of black flies is directed at the larval stages. Ideally, water flow is interrupted for a period of 24 hours. Black fly larvae require high oxygen levels carried by flowing waters and will die if the water flow is stopped. Where this is not possible, larvicides such as Bacillis thuringiensis israelensis (Bti) are used to control black flies. This highly specific larvicide kills larvae by causing gut paralysis and internal ulceration. Non-target organisms are not affected by its use.
Midges are prevalent in the San Gabriel Valley. This small insect is often confused with mosquitoes but does not bite. They are routinely seen hovering in swarms on warm summer evenings. Fortunately, they do not transmit disease or cause significant discomfort.
