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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. Attacks can not only provoke severe reactions in many bitten
individuals, but often have serious social and economic effects.
The experience of being continually bitten, unable to step outside from countless
bites, is a demoralizer with few equals, and if the flies are not deterred with repellents
or controlled by insecticides they can badly disrupt any commercial or recreational
outdoor pursuit in black fly areas.
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.
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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.
Since 1990, the District has implemented a year-round integrated treatment program to
control the
black fly problem in areas of the Santa Monica Mountains (see photo right - technician repelling
down a 200 ft. cliff face into black fly treatment area). This bothersome fly
can be a great nuisance in Malibu, especially around the Malibu Creek/Cold Creek
area. In 1994 and
1995, golfers, hikers, and picnickers at Griffith Park in Los Angeles County were attacked
by black flies. The vicious attacks by the black flies substantially decreased visits to
Griffith Park.
