Anyone who has been to the forest has had experience with these insects and has perhaps asked "what are these annoying flies?" While generally blackflies are only a minor annoyance they may also cause more serious disease.
Blackflies are known to scientists as Simulidae. They are related to mosquitoes and like mosquitoes have an adult stage that flies (and bites!) and larvae that live in water, particularly clinging to rock and stones in flowing forest streams.
In Thailand blackflies are known by many local names. Adult flies are most widely known as "Rin Dam", though here in northern Thailand they are known as "Coon" and the Karen call them "Pa Bor". Doi Inthanon National Park is one of the areas where blackflies have been well studied in Thailand, of the 87 species known from Thailand being reported, an impressive 2/3 are found in Doi Inthanon.
Blackfly are a particular nuisance when visiting the summits of mountains such as Doi Inthanon and Doi Pui when they take the opportunity to suck on your, or your pet's, blood. Generally though they are only a major problem in the morning or evening, though this changes with season.
Though blackfly bites are generally only a nuisance (with minor blood loss, swelling and inflammation) in some cases they may cause a severe allergic reaction and produce flu-like symptoms. Additionally abroad they are reported to be carriers of the parasite Onchocerca volvulus which causes the disease Onchocerciasis (River blindness) in people and pets, and are probably associated with Nodding Disease in Africa. However, there are no reports of disease in this country.
While blackfly do eat humans the reverse is true too! Karen people from Mae Abb in Chiang Mai use them as food. They use branches from nearby bushes to slow the flow of water in a stream and then use their hands to move over rocks. When they blackly larvae are dislodged from the rock they quickly grab onto the hand instead to stop being washed downstream and eventually the hand becomes covered with larvae. The larvae can then be washed and prepared as a spicy salad, with roasted chilli, fermented beans, shallots, onions, lime and , of course, blackfly larvae. This dish is popular especially when taken with the local hooch!A PDF version of this article is available as Bug Bites #1