Yes, no see ums fly. They are tiny flying insects, technically known as biting midges, with a single pair of wings that carry them to hosts for blood meals. Despite being only 1 to 3 millimeters long (smaller than a grain of rice), they are active and deliberate fliers that navigate toward people and animals using specific sensory cues. Their small size and quiet flight are exactly why they earned the name “no see ums.” You rarely spot them before you feel the bite.
How No See Ums Find You in Flight
No see ums don’t just drift randomly through the air. They actively seek out hosts by detecting carbon dioxide, the gas you exhale with every breath. In controlled lab tests, biting midges moved toward a carbon dioxide source 1.8 times more often than toward a neutral control. They also respond to body heat, moisture, and organic odors. This combination of sensory abilities makes them remarkably effective at locating exposed skin, even at dusk or dawn when visibility is low.
Their flight range is relatively limited compared to larger biting insects. Most species stay within a few hundred yards of their breeding grounds, which are typically moist soil, marshes, or decaying organic matter near water. If you’re getting bitten, the source population is usually close by.
Why They’re So Hard to Keep Out
Standard window screens don’t stop no see ums. A typical home window screen has an 18-by-14 mesh count, meaning 18 vertical wires and 14 horizontal wires per square inch. The gaps between those wires are large enough for no see ums to pass right through. Specialty “no see um” screens use a tighter 20-by-20 mesh, with smaller openings (called apertures) that block these tiny fliers. If you live in an area with heavy no see um activity, upgrading porch and window screens to this finer mesh is one of the most reliable physical barriers available.
Wind Disrupts Their Flight
Because no see ums are so lightweight, even moderate air movement makes it difficult for them to fly steadily and land on skin. A ceiling fan or portable fan on a porch can help, but a gentle breeze won’t cut it. The airflow needs to be strong enough to actually prevent the insects from navigating a controlled landing. Positioning fans to create a consistent, noticeable wind across seating areas works better than a fan mounted high overhead pushing air weakly downward. Outdoors on naturally breezy days, no see um activity drops significantly.
Repellents That Work Against No See Ums
Several proven insect repellents are effective at deterring no see ums in addition to mosquitoes. DEET is the most widely tested and works well against biting midges, black flies, and fleas. Picaridin performs similarly against no see ums and chiggers. Both are available in sprays and lotions at various concentrations, with higher percentages lasting longer on skin.
For people who prefer plant-derived options, oil of lemon eucalyptus (the refined compound PMD) is registered for use against no see ums, black flies, gnats, and mosquitoes. It’s sold as towelettes and liquids at 8 to 10 percent concentrations. Another synthetic alternative, IR3535, is the active ingredient in several Avon products labeled for biting midges, no see ums, and sandflies, though these tend to contain lower percentages of active ingredient and may need more frequent reapplication.
When No See Ums Are Most Active
No see ums are most likely to bite during dawn and dusk, though some species are active throughout the day in shaded, humid areas. They thrive in warm, moist environments and are especially common near coastal marshes, mangrove areas, lakeshores, and anywhere with wet soil rich in organic matter. Populations peak in spring and summer in most regions, though in subtropical and tropical climates they can be a year-round problem.
Rain and high humidity increase activity because the adults need moisture to survive. Hot, dry, windy afternoons tend to ground them. Planning outdoor time during the least favorable conditions for no see ums, bright midday sun with a breeze, naturally reduces your exposure. Combining that timing with a fan, repellent, or fine mesh screening covers most of your bases.