Black fly vs No-see-um biting midge

These two are easy to mix up. Here's how to tell a black fly from a no-see-um biting midge, and whether either one bites or stings.

≠The key differences

Black flies are larger, stockier and have humpbacked appearance; larvae attach to flowing water, while Culicoides larvae prefer wet mud and small pools.

⚖︎Side by side

	Black fly	No-see-um biting midge
To humans	Painful bite	Irritating bite
Size	2-5 mm body length	1-3 mm body length
Colours	Black, Dark grey, Pale grey	Brown, Dark brown, Grey
Family	Simuliidae	Ceratopogonidae
Habitat	Larvae and pupae in well-oxygenated running water (streams, rivers); adults in riparian zones, meadows and near livestock.	Breeds in wet, organic-rich mud, margins of ponds, seepages, livestock manure, irrigated soils and other semi-aquatic substrates; adults rest in vegetation near breeding sites.
Range	Widespread in North America; S. vittatum is a species complex with local populations across much of Canada and the United States, especially near rivers and streams.	Primarily western and central North America where recorded; C. sonorensis is part of a species complex found across temperate regions of North America and has been extensively studied because of its role in livestock disease transmission.
Active	Spring to late summer in temperate zones; active during daylight, especially in the morning and evening and on overcast days.	Warm months (regional), crepuscular and nocturnal activity — most active at dawn and dusk.
Pest?	Yes	Yes

🔍How to spot a black fly

Very small size (2-5 mm) and dark, compact body with a humped thorax.
Found near streams and rivers; swarms of tiny biting flies indicate black flies rather than mosquitoes.
Larvae attached to rocks or submerged vegetation with visible filtering fans when examined closely.
Bites typically on exposed skin of face, neck and hands where they can access capillary blood.

Full black fly guide →

🔍How to spot a no-see-um biting midge

Very small size: 1-3 mm body length; visible as tiny flies or specks.
Patterned wings under magnification; wing venation and spots typical of Culicoides midges.
Found swarming near dusk or dawn around moist habitats, livestock or vegetation.
Accurate species-level ID typically requires microscopic examination of wings/genitalia or molecular tests.

Full no-see-um biting midge guide →

?Frequently asked questions

What is the difference between a black fly and a no-see-um biting midge?

Black flies are larger, stockier and have humpbacked appearance; larvae attach to flowing water, while Culicoides larvae prefer wet mud and small pools.

Is a black fly or a no-see-um biting midge more dangerous?

Black fly: Painful bite. No-see-um biting midge: Irritating bite. Female black flies bite to take blood and can cause painful, itchy bites, local swelling, and in heavy exposure allergic reactions or secondary infection from scratching. Female midges bite to take blood.

Identification from photos is never certain: don't handle insects you can't identify, and get medical advice for bites, stings or allergic reactions.