Black flies are considered a pest in many parts of the United States. Only four types of black flies actually feed on humans, most will leave people alone and feed on preferred animals. Although they are considered more of a nuisance than dangerous, they can be a vector for diseases like river blindness. The reason they are not dangerous is because they are not particularly bad when they are alone, the problem is when there are swarms of gnats that can cause tremendous amounts of problems for people and animals. One bite will cause a small irritated spot that swells up and has a slight burning sensations but a swarm of gnats biting you can actually cause people to go into shock. Most of the nuisance to humans comes from the black fly causing a drop in livestock products such as milk or eggs. The gnats can bother livestock and poultry to the point where it can kill a small chicken or just cause them to produce less eggs because of all of the stress from the bites.
The black fly saliva is the source of the toxin that causes the irritable spot when a victim is bit. Even if the gnats are not biting, they can still fly into noses and ears, which can still cause a burning sensation. Places around the United States will have management techniques set up to combat the black fly population depending on the time of year it is because it can cause a reduction in the amount of people using outdoor recreation spots. Pennsylvania actually has the largest management plan in the country when it comes to black flies because of the large population in the state. People have moved away from using repellants for the flies and are now using insecticides such as Bacillus thurgiensis israeliensis because they are less harmful to the environment and is derived from a naturally occurring soil bacteria.
The black fly saliva is the source of the toxin that causes the irritable spot when a victim is bit. Even if the gnats are not biting, they can still fly into noses and ears, which can still cause a burning sensation. Places around the United States will have management techniques set up to combat the black fly population depending on the time of year it is because it can cause a reduction in the amount of people using outdoor recreation spots. Pennsylvania actually has the largest management plan in the country when it comes to black flies because of the large population in the state. People have moved away from using repellants for the flies and are now using insecticides such as Bacillus thurgiensis israeliensis because they are less harmful to the environment and is derived from a naturally occurring soil bacteria.
Onchocerciasis, also known as River Blindness, is caused from the bite of one of the black fly species in the Simulium genus. The symptoms of this disease are itching, bumps under the skin and it eventually leads to blindness. Usually the infection comes from a large amount of bites where they become infected with the parasitic worm Onchocerca volvulus, which lays eggs inside the persons skin and the larvae crawl out of the skin once they have developed. Once the larvae reach the skin, they can now infect another black fly that can spread the disease to another human. The infection can be described in different stages that range from some itching to full blindness. At stages closer to blindness, people can start having skin that looks like lizard skin or leopard skin. River blindness is the second leading cause for blindness due to infection in the world. There is no cure for the infection, only a way to stop the rate at which the worms are reproducing, which slows down the infection attacking the body. No vaccine can be taken to prevent river blindness, only proper techniques to avoid getting bit by black flies can be used to prevent this disease. Since the black flies lay their eggs in running water, this disease is more common in areas that are close to a river or where people spend time on rivers.