What does it look like? 
A black fly is about the size of a small mosquito—about 1/32 to 1/2 inch in length. It is much stockier and tougher than a mosquito. It belongs to the family Simuliidae (Diptera). Because of its small size, it is sometimes known as a buffalo gnat or reed smut.
Where does it live? 
The family Simuliidae is found in various climate conditions, from warm tropical areas to frigid arctic regions. There are more than 1,000 known black fly species worldwide.
The ideal habitat for a black fly would be a mountain forest with cold, fast running water, very little wind, and abundant wildlife. Standing water, ponds, lakes, or swampy areas would be undesirable because flowing water is needed for transporting food and oxygen to the young.
What does it eat? 
Both male and female black flies are attracted to flower nectar. The female feeds on blood to develop her egg laying parts. Humans, animals, and birds are a source of food for most black flies. Some feed only on cold-blooded animals.
Larvae have little mouth brushes that strain food from flowing water. Their food consists of small animals, such as protozoa and crustaceans in the south, or plants such as algae in the north.
How does it defend itself? 
The black fly has little in the way of defense. It plays an important role in aquatic food chains where the egg, larva, and pupa are easy prey for fish, amphibians and birds. The adult rises to the water surface in an air bubble and often becomes trout food.
The ability to fly very fast and the tendency to travel in swarms offer some protection to adults.
What stages of metamorphosis does it go through? 
The life cycle of a black fly includes four stages: egg, larva, pupa, and adult. All of these live in water except the adult. The larvae hold onto rocks just beneath the surface of flowing streams and rivers. The silken cocoon containing the pupa is attached under water. When the adult emerges from its air bubble at the water surface, it immediately goes off to search for food and to mate.
The black fly breeds in running water. Females deposit 150-500 creamy-white eggs in or near the edge of flowing water. The eggs darken until they are almost black just before they hatch. The time required for hatching can be three to five days or as long as 30 days at low temperatures.
Larval development may be complete in just 10 days or it may take up to 10 weeks. Some species live through the winter in the larval stage. In the arctic and other frigid areas, winter is usually passed in the egg stage. Gill filaments allow the larvae to take oxygen directly from the water instead of coming to the surface to breathe.
Pupae also possess special breathing filaments to remove dissolved oxygen from the water. The pupal period varies from as little as 4 days to as long as 5 weeks, depending on water temperature and species. The adult emerges from the pupal case, rises to the surface, unfolds its wings and flies away. The complete life cycle, from egg to adult, varies from 6 to15 weeks.
What special behavior does it exhibit? 
A black fly does a great deal of rapid flying before settling to bite. Even after landing, it moves around and taps on the skin with its front legs to find the perfect “drilling site.” The female black fly is a vicious biter, sometimes leaving a drop of blood behind when she is finished.
How does this bug affect people? 
The adult black fly is a severe pest that affects humans and animals worldwide. It often travels in swarms and is attracted to carbon dioxide in the breath. On humans it looks for exposed areas of skin, especially along the hairline, feet, ankles and arms. Some people may have severe allergic reactions to its bite.
Because it feeds on blood, a black fly can transmit diseases to humans. One such disease is river blindness which affects millions of people in tropical areas.
Black fly bites cause serious diseases in wild and domestic animals. Large black fly populations can cause agricultural losses in production of milk, beef, and eggs. Large swarms may attack livestock causing death by shock or blood loss.
Persistent swarming and biting by some black fly species cause serious annoyance and discomfort to humans. Female adults get into eyes, ears, nose, and mouth in their search for blood. Reduced enjoyment of outdoor activities often results in economic loss for areas dependent on recreation and tourism.
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