No-See-Ums Through Screen Enclosures: Why They Get In and What Actually Keeps Them Out

Yes – standard pool and porch screen enclosures do NOT block no-see-ums (biting midges, Culicoides spp.). Here's why: (1) Size disparity – no-see-ums are 1—3mm in length, far smaller than mosquitoes (6—7mm). Their small size is the source of their name – you often can't see them before they bite. (2) Standard screen mesh size – the most common pool and porch screen is 18x14 mesh (18 threads per inch horizontally, 14 vertically). This mesh has openings of approximately 1.3mm x 1.7mm. A no-see-um at 1—2mm body size can pass through these openings without difficulty. (3) Mosquito comparison – mosquitoes (6—7mm) cannot fit through 18x14 mesh. Standard screen enclosures effectively block mosquitoes. The difference in biting experience between inside and outside a standard screen enclosure is dramatic for mosquitoes but minimal for no-see-ums. (4) Season and wind – no-see-ums are most active at dawn, dusk, and during calm wind conditions when they can fly without being dispersed. They can enter screen enclosures both through the mesh and through any gaps around door frames, where the screen meets the deck, and around pass-through fixtures. (5) Geographic distribution – no-see-ums in Broward and Palm Beach counties are worst near coastal areas, tidal flats, Intracoastal Waterway frontage, and low-lying areas with wet organic material. Homes near these breeding areas see the most severe enclosure intrusion.

To block no-see-ums, you need significantly finer mesh than standard 18x14 pool screen: (1) 20x20 fine mesh ('no-see-um screen') – 20 threads per inch in both directions, with openings of approximately 0.9mm x 0.9mm. This stops most no-see-um species since their body diameter exceeds 0.9mm, though very small Culicoides species can still pass through. Available from most screen suppliers and sometimes called 'Super Screen' or 'Fine Screen.' (2) 20x20 mesh trade-offs: Finer mesh reduces airflow by 25—40% compared to standard 18x14. In South Florida's heat, this can make screened enclosures noticeably warmer and reduce ventilation during the hottest months. Many homeowners find the reduced airflow acceptable given significant relief from no-see-um biting. (3) Installation: Replacing existing pool screens with finer mesh requires re-screening the existing frames – a straightforward job for screen contractors that typically costs $3—$8 per square foot depending on enclosure size and existing frame condition. For large pool cages (2,000+ square feet), re-screening cost may be $6,000—$16,000 depending on market. (4) Partial replacement strategy: Some homeowners replace only the lower panels (from deck level to approximately 6 feet) with fine mesh, since most no-see-um entry occurs at lower levels where they fly near the deck. Upper panels are left as standard mesh to maintain better airflow. This reduces cost while addressing the most impactful entry zone. (5) Gaps matter as much as mesh – even 20x20 fine mesh won't fully stop no-see-ums if there are gaps around the door frame, where the screen meets the concrete deck, or around lighting and plumbing pass-throughs. Seal all gaps when upgrading to fine mesh.

If no-see-ums are biting inside your screened pool enclosure specifically at dusk and dawn, the pattern reflects both their behavior and the limitations of standard screen mesh: (1) Peak activity timing – Culicoides biting midges are most active during the 30—90 minute windows around sunrise and sunset when wind speeds are typically lowest. Wind above 10 mph grounds them effectively. The calm conditions inside a screen enclosure (protected from outdoor breezes) are actually ideal no-see-um conditions compared to windier exposed areas. (2) Thermal gradient at dusk – as the sun sets, the concrete deck inside your pool enclosure releases accumulated heat, creating a warm column of air that attracts CO₂-seeking no-see-ums. Your body and the warm deck environment both signal a prime feeding opportunity. (3) Entry mechanism – no-see-ums enter primarily through the standard screen mesh (too small to stop them), through gaps around doors, and through any openings near the deck level. They don't need to find a large gap – the mesh itself is the entry point for most standard enclosures. (4) Accumulation effect – once inside, no-see-ums find it harder to exit than enter (they don't seek openings the same way they entered). Over an evening, the enclosure can accumulate more no-see-ums than are in the immediate outdoor environment. (5) Coastal and waterway properties – no-see-um pressure inside screen enclosures is most severe for properties near the Intracoastal Waterway, tidal areas, coastal mangroves, and wet organic material. These breeding source areas produce much higher local no-see-um densities than inland properties.

Several approaches reduce no-see-um pressure inside and around screen enclosures: (1) Professional barrier spray on enclosure exterior and surrounding vegetation – treating the vegetation and surfaces outside the enclosure with residual spray reduces the adult no-see-um population that's approaching the structure. Our MPB formula applied to trees, shrubs, and ground cover around the enclosure creates a contact-kill zone where no-see-ums land before entering. This is the most effective outdoor approach. (2) Treating inside screen enclosure surfaces – we can apply a diluted perimeter spray to the inside lower-surface panels, around the door frame interior, and on the screen itself. This creates a contact-kill zone where no-see-ums land after entering through the mesh. Note: the treatment is not applied directly to the pool water, furniture, or deck. (3) Oscillating fans – a strong box fan or oscillating fans directed at sitting areas create air movement above the 10 mph threshold that grounds no-see-ums. This is a highly effective immediate measure that requires no chemical treatment. (4) Personal repellent inside the enclosure – DEET or picaridin applied before enclosure use provides personal protection when other measures are insufficient. (5) Fine mesh upgrade – if no-see-um pressure inside the enclosure is chronic and severe, re-screening with 20x20 fine mesh is the long-term structural solution. It can be done in phases (lower panels first) to manage cost. (6) Peak-hour avoidance – planning pool enclosure use for the 9am—4pm window (between no-see-um activity peaks) significantly reduces biting exposure without any treatment.

Yes – Mosquito Shield's MPB formula is effective against no-see-ums as well as mosquitoes. The same biweekly barrier spray that targets mosquito resting vegetation also addresses the adult no-see-um population in and around your property: (1) What the treatment covers: Application to the exterior vegetation around your pool enclosure and property perimeter depletes the adult no-see-um population approaching your outdoor spaces. Application to the grass immediately around the enclosure reduces the ground-level no-see-um population that lives in mulch and organic debris. (2) Treatment inside the enclosure: On request, we can apply a targeted spray to the interior perimeter of the enclosure – primarily the lower screen panels, the inside of the door frame, and ground-level entry points. (3) Realistic expectations: Barrier spray significantly reduces but does not eliminate no-see-um pressure, especially on coastal and Intracoastal properties with very dense breeding source populations nearby. Fine mesh re-screening is a permanent structural solution that barrier spray cannot replicate for severe no-see-um enclosure intrusion. (4) Our no-see-um coverage is included in the standard Mosquito Shield service – there's no add-on fee for no-see-um treatment. If no-see-ums are your primary concern in addition to or instead of mosquitoes, let us know when you schedule so we can specifically address those areas during your initial treatment. Contact us at 561-443-3333.