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Black fly

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Black flies are small insects belonging to the family Simuliidae. They are often described as black or gray with short legs and antennae.

Black Fly
Black Fly

There are over 2,200 formally named species of black flies in the world. Only 15 of these species are currently known to be extinct. Most species belong to the genus Simulium, which contains over 1,800 different types. These flies are important to study because they interact deeply with human health and local ecosystems. They can be a nuisance to people and livestock, and some species act as vectors for diseases.

The life cycle of a black fly begins in flowing water, also known as lotic habitats. Females lay their eggs in these moving streams. The larvae then attach themselves to submerged rocks using tiny hooks on their abdomens.

Black Fly Attack on theDubawnt River Nunavut
Black Fly Attack on theDubawnt River Nunavut

To stay in place, they use silk threads called holdfasts. These larvae feed using specialized structures called mouth brushes. These are foldable fans surrounding their mouths that expand to catch organic particles, algae, and bacteria passing by in the current. The larva scrapes this collected food into its mouth every few seconds. Eventually, they pupate underwater and emerge as flying adults inside a bubble of air.

Black flies have a fascinating symbiotic relationship with bacteria to help them grow. Research conducted at Portsmouth University between 1986 and 1987 revealed how this works. The larvae create highly acidic conditions within their midguts. This acidity is perfect for specific bacteria that can metabolize cellulose. While insects cannot digest cellulose on their own, these bacteria turn it into basic sugars. This provides essential nutrition for both the larvae and the bacteria. This adaptation allows them to thrive in fresh-flowing streams where other food might be scarce.

Adult black flies have different feeding habits depending on their sex. Both males and females consume nectar or honeydew to get the carbohydrate energy needed for flight. However, most females exhibit anautogeny, meaning they need extra nutrients to produce eggs. To get these nutrients, females bite birds or mammals, including humans, to feed on blood.

Black Fly
Black Fly

The mouths of males are not designed to bite through skin. Some species can disperse tens or even hundreds of miles from their breeding sites. They use their own power and the help of prevailing winds to travel long distances. This ability to move makes it very difficult for humans to control their populations.

Black flies can cause significant issues for human populations and animals. In North America, populations swell from late April to July in places like Canada and New England. In Canada, they are a scourge to livestock and can cause weight loss in cattle. In some cases, the saliva of a specific species can cause anaphylactic shock and death. In England, the Blandford fly once caused painful lesions and required medical treatment in 2010. Because of these issues, many regions have control programs. Pennsylvania, for example, operates the largest single black fly control program in North America.

When a black fly bites, it uses a specific mechanical process. The fly uses teeth on its labrum to stretch the skin. It then uses its maxillae and mandibles to abrade the skin. This action cuts the skin and ruptures fine capillaries to reach the blood. To make feeding easier, the fly's saliva contains a powerful anticoagulant. This substance also partially numbs the site of the bite. This numbing effect reduces the host's awareness, allowing the fly to feed for a longer time. Bites often result in itching, swelling, or inflammation.

Beyond simple irritation, black flies are central to spreading serious diseases. They are the primary vector for the parasitic nematode Onchocerca volvulus. This parasite causes a disease known as onchocerciasis, or river blindness. This condition is endemic in parts of Africa, South America, and the Arabian Peninsula. The parasite lives on human skin and is transferred to the fly during a blood meal. Additionally, intense feeding can lead to "black fly fever." This condition includes symptoms like headache, nausea, fever, and aching joints. These symptoms are likely a reaction to compounds found in the fly's salivary glands.

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Black Fly.png
File:Black Fly Attack on theDubawnt River Nunavut.jpg
Black Fly Attack on theDubawnt River Nunavut.jpg
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