Los Angeles County West Vector & Vector-Borne Disease Control District

Black Flies

    Black flies are small, dark flies with a humped back that can give a painful bite. Unlike a mosquito (which  sucks up blood through a proboscis), black flies slash the skin and lap up the pooled blood.  Their  larvae (left) and pupae (below) usually attach themselves to rocks and vegetation in flowing streams.  They belong in the order Diptera (Flies), to the family Simuliidae.

    Black flies are feared in many regions because of the relentless and intolerable nature of their attacks, not only on man, but on livestock, poultry, and wildlife. Bites can not only provoke severe reactions in many bitten individuals, but often have serious social and economic effects. Black flies can reduce the milk output of dairy cows. When a comparison of the expected and actual milk yields was made on a California dairy farm where cows were under attack, a clear loss of production was found to be correlated with high levels of biting.

    In other countries, black flies are also carriers of the filarial disease Onchocerciasis, commonly referred to as River Blindness. A blackfly carrying larvae of Onchocerca volvulus bites a victim and transmits the infection. The larvae grow into groups of string-like worms that live wrapped up in a bump under the skin. Adult female worms produce thousands of tiny microfilariae for approximately 8-12 years. Unlike the adults, the microfilariae migrate throughout the victim's skin, causing skin disfigurement and intense itching. The worms can cause permanent damage when they reach the eyes, impairing sight and finally causing blindness. When another blackfly bites the victim and then bites an uninfected person, it begins the cycle of infection again.




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