Insect identifier · Biting flies
How to identify a Black fly
Simulium spp.
· Also called buffalo gnat, blackfly, simulium, buffalo gnat identification, black fly bite, blackfly vs mosquito
Black fly vs mosquito: humped back (“buffalo gnat”), daytime face and ear bites near rivers, infamous in the North Woods in late spring.
Humped back, rivers, daytime, ears and hairline. Buffalo gnat years in the North Woods are a head-net problem. They are not mosquitoes. Peak often follows snowmelt. DEET plus clothing. Swollen ears after a river day are this page, not a mystery infection, unless redness spreads or fever starts.
What does a black fly look like?
Small, 1–5 mm, humped thorax, short antennae. Need running water to breed. Swarm around face, ears, and hairline.
Black fly (Simulium spp.) is Small, 1–5 mm. Colors people notice: black, gray. Field marks: Humped thorax (“buffalo gnat”); Short antennae; Swarm around face, ears, and hairline; Need running water to breed. It is found outdoor. If those marks are missing, open No-see-um, Northern house mosquito before you force this name. Search phrases that belong on this page include what a black fly looks like and black fly identification.
Identification marks
- Humped thorax (“buffalo gnat”)
- Short antennae
- Swarm around face, ears, and hairline
- Need running water to breed
Size: Small, 1–5 mm
Colors: black, gray
Where: outdoor
What a typical black fly bite looks like
Painful prick then an itchy, swollen welt. Ears and neck often swell. Head nets in peak season.
People searching “black fly bite identification” want the pattern, not a single anonymous bump. Painful prick then an itchy, swollen welt. Ears and neck often swell. Some people get dramatic local swelling. Immediate steps on this page: Get indoors or to moving air; Cool compress; balm on intact skin; Oral antihistamine per label if swelling is large; Seek care for breathing difficulty (rare allergy). This species does bite or sting people. Fever, spreading redness, trouble breathing, or a child with many stings is professional care.
If you were bitten
- Get indoors or to moving air
- Cool compress; balm on intact skin
- Oral antihistamine per label if swelling is large
- Seek care for breathing difficulty (rare allergy)
Black fly vs No-see-um
Humped back, daytime, rivers, ears and hairline. Mosquitoes have longer legs and a different hum. No-see-ums are even smaller and more dusk/coast.
- No-see-um identification (Culicoides spp.)
- Northern house mosquito identification (Culex pipiens)
- Sand fly identification (Lutzomyia spp.)
Range and season
Wherever there is fast clean water. Often May–June in the North.
Clean running water: North Woods, mountains, and spring hatch zones.
Wherever there is fast, clean flowing water. Infamous in the North Woods, mountains, and Canada in late spring.
Late spring “black fly season”; some areas have a second generation
Common questions
Black fly vs mosquito?
Black flies have a humped back, shorter bodies, and bite by day near rivers. Mosquitoes are longer-legged and often dusk biters.
Do they carry disease in North America?
River blindness is not a North American issue. Here they are a severe nuisance; livestock can suffer more than people.
When is black fly season?
Often May–June in the North, earlier in the South, tied to snowmelt and spring flows.