Biting gnats (no-see-ums / biting midges)
Culicoides spp.
Quick answer
Biting gnats — the tiny midges many call "no-see-ums" (Culicoides) — are not mosquitoes, but tiny (1–3 mm) flies whose bite is far larger than they are. The females bite for blood, mostly at dawn and dusk in calm conditions, breed in moist soil, mud, and wet organic matter near water, and slip through standard insect screens. Many are CO₂-responsive, so a CO₂ + heat trap also catches them — which is why the homepage groups them with mosquitoes.
Biology & identification
Culicoides biting midges are minute flies (1–3 mm — small enough to pass through 16-mesh window screens, hence "no-see-um"). Like mosquitoes, only females bite, using scissor-like mouthparts that produce a sting and an itchy welt out of proportion to their size.
They do not breed in open standing water like mosquitoes; larvae develop in semi-aquatic habitats — moist mud, salt-marsh and mangrove edges, wet sand, manure, decaying vegetation, and the muck around pond and lake margins.
They are weak fliers and concentrate near their breeding habitat, which is why coastal, marsh, and lakeside properties suffer most. Activity is strongly suppressed by wind — even a light breeze grounds them.
Peak activity — when it bites
Crepuscular — biting peaks at dawn and dusk, especially on warm, humid, calm (low-wind) evenings.
Wind is the dominant limiter; they are worst when the air is still.
Why it bites — host-seeking
Females need a blood meal for egg development, like mosquitoes.
Many Culicoides are attracted to CO₂ and host odors, which is the behavioral overlap that lets a mosquito trap catch them too. Black flies (Simuliidae) are blood-seekers drawn to the same CO₂ and body heat, so they get caught incidentally the same way.
How the CO₂ trap targets it
A genuine bonus target. Because many biting midges host-seek by CO₂, a CO₂ + heat trap also captures no-see-ums (Kline/USDA-ARS work with Culicoides and CO₂ traps supports this), which is why we group them with mosquitoes. Black flies (Simuliidae) host-seek the same warm, breathing-host way, so they too get drawn in and caught incidentally alongside mosquitoes — no efficacy number attached, just the same mechanism.
Honest notes: their tiny size and wind-sensitivity mean the same low-wind conditions that make them bite are when the trap is most useful; the plume also shears apart in the breeze that grounds them. The trap reduces biting pressure; for personal protection, fine-mesh "no-see-um" netting (smaller than mosquito mesh) and skin repellent are the complements.
It won’t touch fungus gnats, fruit flies, or drain flies — those chase moisture and rot, not breath, and this trap only speaks the language of host-seekers.
Range & vector status
Primarily a severe nuisance in the U.S.; some Culicoides transmit animal pathogens (bluetongue and EHD in livestock and deer) but are minor human-disease vectors domestically.
Worst in coastal, salt-marsh, and lakeside regions (Gulf and Atlantic coasts, Florida, parts of the Upper Midwest). Factual, nuisance-first framing — no fear-mongering.
Sources
- University of Florida IFAS, "Biting midges (Culicoides spp.)" Featured Creatures.link pending verification
- Kline, D.L. & colleagues, CO₂ trapping of Culicoides.link pending verification
- Mullen, G.R. & Murphree, C.S., "Biting Midges (Ceratopogonidae)," in Medical and Veterinary Entomology.link pending verification
Common questions
Does it catch biting gnats?
The biting kind, yes — incidentally. Biting gnats (the midges some folks call "no-see-ums") and black flies are blood-seekers drawn to the same CO₂ and body heat the trap puts out, so they get caught alongside mosquitoes. "Gnat," though, also covers non-biting flies — fungus gnats, fruit flies, drain flies — that chase moisture and rotting or fermenting matter, not a host’s breath. The trap isn’t built for those and won’t meaningfully control them.
Are no-see-ums mosquitoes?
No. No-see-ums are biting midges (Culicoides), a separate family of tiny 1–3 mm flies. They share the blood-feeding, CO₂-seeking behavior of mosquitoes, which is why a CO₂ trap catches them too.
Why do no-see-ums get through window screens?
They are small enough (1–3 mm) to pass through standard 16-mesh screens. Fine-mesh "no-see-um" netting, which is tighter than mosquito mesh, is needed to exclude them.
When are no-see-ums worst?
At dawn and dusk on warm, humid, calm evenings near water. Wind is the dominant limiter — even a light breeze grounds them.