No-see-ums are tiny biting flies found throughout Florida, especially near coastal areas, salt marshes, and anywhere with moist soil. They measure only 1 to 3 millimeters long, small enough to pass through standard window screens, and their bites pack a sting far out of proportion to their size. If you’re visiting or living in Florida, here’s what you need to know about these insects and how to deal with them.
What No-See-Ums Actually Are
No-see-ums belong to the genus Culicoides, a group of biting midges with over 1,000 species worldwide. Several species thrive in Florida’s warm, humid climate. They breed in wet environments: salt marshes, mangrove swamps, muddy shorelines, and even moist soil in residential yards. Females need a blood meal to produce eggs, which is why they bite.
Their name is literal. These insects are so small that most people never see them. You’ll feel the bite before you spot the bug, and by then it may already be gone. They’re sometimes called sand flies, sand gnats, or punkies, though these names can refer to different insects in other parts of the world.
When They’re Most Active
No-see-ums are present in Florida year-round, but their peak season hits in June and July. South Florida tends to have the worst infestations due to the combination of heat, humidity, and abundant coastal breeding grounds. Even outside peak months, warm spells can bring them out in force.
They feed most aggressively at dawn and dusk. Some species also bite throughout the night. Midday, when the sun is strongest and humidity drops, is generally when you’ll encounter the fewest. Wind is your ally: no-see-ums are weak fliers, and a steady breeze above about 5 mph keeps them grounded. This is why screened porches with ceiling fans are a Florida staple.
What Their Bites Feel and Look Like
The initial bite produces a sharp, stinging or burning sensation that’s hard to miss despite the insect’s size. Within minutes, a small red welt appears at the bite site. For most people, the discomfort fades within a few hours. But if you’re sensitive to the bites, or if you’re a visitor without prior exposure, the reaction can be significantly worse.
Tourists and newcomers to Florida often get the most dramatic reactions. Bites can swell to several centimeters across, blister, become weepy, and itch intensely for days or even weeks. Some people don’t notice the itching until hours after being bitten, which makes it easy to accumulate dozens of bites in a single outdoor session without realizing it. People who live in affected areas long-term often develop a degree of desensitization, eventually reacting mildly or not at all.
Disease Risk in Florida
In parts of South America, the Caribbean, and Sub-Saharan Africa, biting midges transmit serious pathogens, including parasitic worms and the Oropouche virus. In Florida, however, no-see-ums are not considered significant disease vectors for humans. The primary concern is the bite reaction itself. That said, scratching bites aggressively can break the skin and lead to secondary bacterial infections, which is the most common complication.
Repellents That Work
Not all insect repellents perform equally against no-see-ums. The ones with proven effectiveness include:
- DEET: The most widely tested option. Products with up to 30% concentration work well against biting midges, and higher concentrations aren’t recommended. A 20 to 30% DEET product gives several hours of protection.
- Picaridin: Effective against no-see-ums, mosquitoes, and chiggers. It has a lighter feel on the skin than DEET and doesn’t damage plastics or synthetic fabrics.
- Oil of lemon eucalyptus (PMD): A plant-derived option that’s specifically labeled for no-see-ums. It provides shorter protection windows than DEET, so you’ll need to reapply more often.
- IR3535: Found in several Avon products, this compound is registered for use against biting midges, black flies, gnats, and mosquitoes, though it tends to come in lower concentrations.
Apply repellent to all exposed skin, not just arms and legs. No-see-ums will bite ankles, the backs of knees, hairlines, and ears. Reapply after swimming or heavy sweating.
Keeping Them Out of Your Home
Standard window screens in most Florida homes use 18×16 mesh, meaning 18 strands per inch in one direction and 16 in the other. No-see-ums slip right through those gaps. If you’re dealing with an infestation near your home, you need a finer mesh: 20×20 weave is the standard for no-see-um screening. This tighter pattern blocks the tiny flies while still allowing airflow, though it does reduce ventilation compared to regular screening by a noticeable margin.
Many Florida homeowners install no-see-um mesh on lanais and porches rather than replacing every window in the house. Pairing fine mesh with a ceiling fan creates a zone where no-see-ums simply can’t operate. For sliding doors and entryways that open frequently, magnetic screen doors with the tighter mesh can help.
Other Ways to Reduce Exposure
Beyond repellent and screens, a few practical strategies make a real difference. Avoid spending extended time outdoors during dawn and dusk, particularly near water or marshy areas. If you’re at the beach in the evening, sitting in a breezy spot or near a bonfire helps, since no-see-ums avoid both wind and smoke.
Wearing light-colored, long-sleeved clothing creates a physical barrier. Tight-weave fabrics work better than loose knits. Some people treat their clothing with permethrin, a contact insecticide that remains effective through several washes and kills no-see-ums on contact.
For yards, reducing standing water and keeping soil well-drained limits breeding habitat close to your home. Professional misting systems that spray a fine insecticide around a property’s perimeter are popular in parts of South Florida, though their effectiveness varies depending on proximity to natural breeding grounds like mangroves and salt flats that you can’t control.
Treating the Bites
Resist scratching, which is easier said than done. Applying a cold compress or ice pack to fresh bites helps reduce swelling and dulls the itch. Over-the-counter hydrocortisone cream or calamine lotion can manage the itching for mild reactions. Oral antihistamines help when you’ve been bitten multiple times and the itching is widespread.
If bites blister or weep, keep them clean and dry to prevent infection. A simple antiseptic wash is enough for most cases. Bites that become increasingly red, warm, or swollen days after the initial reaction may indicate a secondary infection that needs attention.