No-see-ums are present throughout Arizona, from the low desert around Phoenix and Tucson to higher-elevation areas near rivers, lakes, and irrigated landscapes. These tiny biting flies, technically called biting midges (family Ceratopogonidae), are small enough to pass through standard window screens and deliver bites far out of proportion to their size. If you’ve been getting bitten by something you can’t see, especially near water or damp soil, no-see-ums are a likely culprit.
What No-See-Ums Are
No-see-ums belong to the genera Culicoides and Leptoconops. Surveys of the southwestern United States, including Arizona, have documented dozens of species in the region. Adults are only 1 to 3 millimeters long, roughly the size of a pinhead, which is why most people never spot the insect responsible for their bites. They’re gray or black, with short wings, and unlike mosquitoes they fly silently.
Both males and females are a nuisance outdoors, but only females bite. They need a blood meal to develop eggs, much like mosquitoes. Their tiny mouthparts slice into skin rather than piercing it, which is part of why the bites feel disproportionately painful for such a small insect.
Where They Live in Arizona
No-see-ums thrive near moisture. In a state as dry as Arizona, that narrows down their habitat to specific spots: riverbanks, irrigation canals, stock ponds, lake shores, and anywhere that soil stays consistently damp. They show up in both low-desert valleys and mountain areas, so elevation alone won’t protect you.
In urban and suburban settings, they breed in surprisingly small amounts of standing or moist material. Over-irrigated lawns and mulch beds, tree holes that collect rainwater, puddles at construction sites, indoor plant pots with soggy soil, and even the drip line from an air conditioning unit can produce enough moisture for no-see-um larvae. If your yard has any patch of ground that stays muddy, that’s a potential breeding site.
They appear in the largest numbers during summer, but Arizona’s warm winters mean some species can be active year-round in lower elevations. Dawn and dusk are peak biting times, though they’ll bite throughout the day in shaded or humid areas.
What Their Bites Look and Feel Like
A no-see-um bite typically starts with a sharp, burning sting at the moment it happens. After that initial pain, the reaction varies widely from person to person. Some people develop a small reddish welt at the bite site. Others, especially those who aren’t regularly exposed, can get swollen, red welts several centimeters across.
One distinguishing feature compared to mosquito bites: itching from no-see-um bites sometimes doesn’t start for hours after the bite occurs. You might not realize you were bitten until well after you’ve gone inside. The bites can also blister, become weepy, and persist for days or even weeks, which is unusual for a typical mosquito bite that fades within a few days.
People who live in areas with regular no-see-um activity often become desensitized over time, eventually experiencing only mild reactions or none at all. Visitors and newcomers to Arizona tend to have the worst reactions. If you’ve recently moved to an area near a canal or irrigated green space and you’re suddenly covered in intensely itchy welts you don’t remember getting, no-see-ums are a strong possibility.
Disease Risk
No-see-ums in the United States are not known to transmit any diseases to humans. That’s one piece of good news. The main concern is the discomfort and potential for secondary skin infections if bites are scratched open.
They do transmit Bluetongue virus to livestock, which is a significant concern for cattle and sheep ranchers in the western U.S. This virus does not infect humans.
Keeping Them Out of Your Home
Standard window screens have mesh openings large enough for no-see-ums to fly right through. If you’re finding bites after sitting near an open window, this is almost certainly why. Regular screens are designed to block mosquitoes and larger insects but can’t stop something the size of a biting midge.
No-see-um screens use a finer mesh, typically rated at 20×20 (20 threads per inch in each direction), with a mesh openness of 59% or less per square inch. That’s tight enough to block even the smallest biting insects. The tradeoff is reduced airflow and slightly less visibility compared to standard screens, but in areas with heavy no-see-um activity, the difference in comfort is dramatic. These screens are available as custom replacements for existing window frames.
Ceiling fans and portable fans also help. No-see-ums are weak fliers, and even moderate air movement makes it difficult for them to land and bite.
Repellents That Work
DEET is the most reliable repellent against no-see-ums. Products with up to 30% concentration are effective and considered the upper recommended limit. DEET works well specifically against biting midges, not just mosquitoes.
Picaridin is another option that performs well against no-see-ums, particularly at higher concentrations. It has the advantage of being less greasy and less likely to damage plastics or synthetic fabrics than DEET. Oil of lemon eucalyptus (listed on labels as PMD) at 8 to 10% concentration is a plant-based alternative that’s labeled for no-see-ums. IR3535, the active ingredient in some Avon products, is also registered for biting midges, though these products tend to have lower concentrations of active ingredient and shorter protection times.
Whichever repellent you choose, apply it to all exposed skin. No-see-ums will find any gap. Long sleeves and pants help reduce the skin area you need to cover, but the insects can bite through thin, tight-fitting fabric, so looser clothing works better.
Reducing Breeding Sites Around Your Property
Because no-see-ums breed in moist soil and organic debris rather than open standing water like mosquitoes, the control strategy is different. Focus on eliminating unnecessary moisture. Adjust irrigation so lawns and mulch beds dry out between watering cycles. Fix leaky outdoor faucets. Make sure air conditioning condensate drains away from the house rather than pooling near the foundation. Clear tree holes of standing water when you can.
If you have potted plants indoors, avoid overwatering. Soggy potting soil is a documented breeding habitat for no-see-ums, and once they establish indoors, they can become a persistent problem that people mistake for other insects.
Yards adjacent to irrigation canals, golf courses, or retention basins may always have some level of no-see-um activity regardless of what you do on your own property. In those situations, fine-mesh screens, fans, and repellents are your primary defenses.