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.
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.
Pest Status:
Adult females produce a painful bite that can cause localized swelling and in extreme cases anaphylactic shock.
Control:
Individuals should not try to control black fly larvae.
Treating a small area, or part of a single stream will do little to alleviate a black fly pest problem.
Control of black files in the adult state is usually not practical, unless you wish to obtain temporary
relief (hours) on local property. Fogging to control black flies in the adult stage may provide a brief
period of relief, but because adults are strong fliers, relief usually is only temporary.
Sustained control is not possible using this method.
Proper clothing offers good protection against black fly bites.
Keep shirt sleeves and front closely fastened and tuck trousers inside socks or high boots.
Zippered front shirts will keep flies out better than button shirts. Light colors such as orange,
yellow and light blue are less attractive to black flies than dark ones such as green, brown and red.
Shoulder-length head nets are sometimes useful. These can also be impregnated with repellents.
Black flies are active only during the day. They do not bite at night. Depending on weather,
black flies tend to be more active at certain times of day. Activity peaks tend to occur around
9:00 to 11:00 AM and again from 4:00 to 7:00 in the late afternoon and early evening, or until
the sun falls below the horizon. They tend to be most active on humid,
cloudy days and just before storms. If possible, avoid activity during times when black flies
are most active. Early morning, midday and late evenings are the best times to work outside.
The same repellents used for mosquitoes are effective against black flies.
