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No-see-ums are true flies, not a smaller relative of mosquitoes, and their size is exactly why standard window screens don’t stop them. Most porch and window screens are built around 18 mesh, sized to block mosquitoes. No-see-ums measure only one to three millimeters, small enough to pass straight through a mesh count built for a much larger insect, which means a house can have perfectly good screens and still let them in every evening.
Why They Cluster Near the Water
No-see-ums lay eggs in damp organic matter near standing water and marsh edges, conditions common anywhere close to the bay or a canal, much less common a few miles inland. That’s why waterfront properties in towns like Belleair and Safety Harbor tend to get hit harder than inland neighborhoods, even ones just a few miles away with otherwise similar landscaping.
Their bites also tend to hurt worse and itch longer than a typical mosquito bite for most people, which makes the size mismatch with standard screens more than just an inconvenience. Unlike a mosquito’s proboscis, which pierces skin to draw blood, a no-see-um actually cuts the skin’s surface and laps up blood from the wound, and it’s the anticoagulant in their saliva that keeps the area itching for days after the bite itself is long over.
PRO TIP
Check your existing screens before buying anything new. Most standard porch screens are around 18 mesh, built for mosquitoes, and no-see-ums slip right through. You need 20 mesh or finer, which is usually a special order, not the standard roll at most hardware stores.
What Actually Helps
Fans do more real work than most people expect, since no-see-ums are weak fliers and can’t handle moving air. Running a porch fan during dawn and dusk, when they’re most active, cuts exposure meaningfully alongside properly sized screens. A single oscillating fan pointed steadily across a porch or patio seating area is usually enough to keep the airflow strong enough to matter.
Their range is also shorter than most people assume. No-see-ums rarely travel more than a few hundred feet from where they hatched, which is why one neighbor’s yard can be miserable while another just a block away barely notices them at all. That short range is actually useful information: a bad no-see-um problem almost always points to a breeding site somewhere close by, not something drifting in from farther away. Checking a neighbor’s low-lying, damp landscaping or a nearby retention area is often more useful than assuming the source is somewhere in your own yard at all.
Screens and fans handle a lot, but a professional misting treatment targeting resting vegetation is what actually knocks the population down instead of just reducing exposure while you’re outside. Our flying insect control program covers exactly this.
