Common Name: Blackfly
Scientific Name: Simulium sp.
Description: Adult flies are small (1-5 mm) and vary in color by species, usually being black or gray, light tan or yellow. Adults are typically robust with a characteristic arched or humped back (prothorax) giving rise to the common name, “buffalo gnat.” Blackfly species are common along fast moving rivers at certain times of the year, particularly in northeast Texas. There, various confined birds have been killed because of attacks by large numbers of black flies.
Another group of tiny biting flies are the biting midges called “punkies” or “no-see-ums” (Diptera: Ceratopogonidae). Usually less than 1/16 inch long, these midges are often mistaken for black flies. However, they can be distinguished by the difference in antennae (black fly antennae are short and stout whereas the ceratopoginid antennae are longer and hair-like) and wing venation (black flies have strong distinct veins toward the front edge of the wing whereas ceratopogonids do not).
Life Cycle: Females deposit 150-500 creamy white eggs that darken until they are almost black just prior to hatching. The eggs usually are deposited singly or in masses in moving water or on some convenient object near the water’s edge. The water may be a slow-moving stream, but most species prefer rapidly flowing water. In rare cases, breeding may occur in marshy areas. The time required for hatching varies with the species and may be 3-5 days or as long as 30 days at low temperatures. Larvae most often are found just beneath the surface of rapidly flowing water. They do not come to the surface to breath like mosquito larvae because the gill filaments of larvae extract oxygen directly from the water. Duration of larval development, like the egg stage, varies with species and temperature and ranges from 10-14 days to 7-10 weeks. Some species overwinter as larvae, although in northern areas, winter is usually passed in the egg stage. The last larval instar spins a reddish-brown, basket-like cocoon in which pupation occurs. These cocoons are attached to slightly submerged objects such as rocks, logs, roots and other debris. Pupae also possess respiratory filaments with which they remove dissolved oxygen from the water. The pupal period varies from 4-5 days to as long as 3-5 weeks, depending on water temperature and species. Adults emerge from the pupal case, rise to the water surface, unfold their wings and fly away. Mating usually occurs shortly after the initial flight. The complete life cycle, from egg to adult, varies from 6-15 weeks and the number of generations per year ranges from one to six, depending on species and climatic conditions.
Habitat and Food Source(s): Larvae are filter feeders and adult females have mouthparts modified for biting and blood feeding. Larvae of most species feed on small animals, such as protozoa and crustaceans, or plants such as algae, by straining particulate matter from water flowing by them with the aid of mouth brushes; some species feed in the silt or on submerged surfaces. Adults feed on the nectar of flowers; only the female requires a blood meal for ovarian development. Although a given species may prefer a particular animal host, most will readily feed upon other host species as well. Black flies attack man and a wide variety of domestic and wild animals and birds; others feed only on cold-blooded animals. Adults can be collected using a sweep net swung around ones head in areas and at times of the year when adults are active. Larvae and pupae can be found on rocks in the shallow water of waterfalls.
Pest Status: Adult females produce a painful bite that can cause localized swelling and in extreme cases anaphylactic shock.
Literature: Bay & Harris 1988; James & Harwood 1969.