Tiny Bugs Are Getting Through Your Window Screens

If specks keep turning up on the inside of a window and the screen has no holes in it, the screen is not failing. Ordinary window screening is sized to stop a housefly. Several of the insects crossing Northeast Ohio yards in October are about a tenth of an inch long, and they walk straight through the mesh.

The usual one here is the hackberry psyllid, a gnat-like insect that spends its summer inside a gall on a hackberry leaf. Ohio State University Extension has been reporting them in Ohio homes on the first cool snap of the fall for years. They are harmless, they do not breed indoors, and most of what people reach for to stop them does nothing.

Why An Undamaged Screen Lets Them Through

A screen is a size filter rather than a seal, and this insect is under the size it filters. Nebraska Extension in Lancaster County puts a number on it: in September and October, people who have hackberry trees notice tiny greyish bugs gathering on their homes, on window screens, front doors and siding, and at a tenth of an inch long they are small enough to pass through ordinary window screen. Kansas State University entomologists say it in one line, that the small size of these insects allows them to penetrate mesh screens and invade homes.

University of Minnesota Extension adds the part that explains the volume, describing them as small enough to pass through most window screens and a nuisance in fall. So the thing people call to describe, dozens of specks inside a closed room with no visible way in, is an ordinary screen meeting an insect it was never rated for.

Where They Come From, And Why Now

From a tree, on a schedule the weather sets. The adults develop inside the bumpy galls on hackberry leaves and leave them in late summer and early fall. Ohio State University Extension, writing in its Buckeye Yard and Garden Line, describes what happens next: the psyllids feed heavily in late summer to build up fat, then look for sheltered places where cooler temperatures slow their metabolism down, so that stored fat carries them through a winter with nothing to eat.

A heated house is the best sheltered place on the block. The same Ohio State coverage names what pulls them toward it and where they end up: heat off sun facing walls and roofs, warmth leaking from inside, then attics, wall voids and the gaps around door and window frames. Damaged siding, torn screens and a worn sweep on a garage door are on that list too. An earlier issue described the window version directly, with psyllids emerging from hackberry leaf galls and collecting around screens, drawn by light or heat from the house.

One fact takes most of the worry out of it. University of Minnesota Extension notes that they do not reproduce indoors. Whatever got in is a fixed number that only gets smaller, not a population setting up behind the drywall.

What Works On Them, And What Does Not

Extension services across the Midwest have published on every obvious idea here, and for once they agree with each other. This is where each one lands.

Is Something Biting Me, Or Is That In My Head?

Nothing is drawing blood. The University of Wisconsin Insect Diagnostic Lab is direct about it: psyllids do not feed on blood and do not inject venom, although their probing can feel unpleasant. Nebraska Extension lists them as not harmful to people or pets and says they will not attack house plants, stored products or furnishings. Texas A&M describes the adults as medically harmless.

You feel them because they land on you. University of Kentucky entomologists note that psyllids are attracted to light colored surfaces and clothing, which is why a white shirt on a porch in October picks up more of them than the porch rail does. If something really is biting, and the marks are showing up overnight in bed rather than outside on a warm afternoon, that is a different question and belongs in a proper bed bug check rather than at the window.

Nothing Sprayed On The Tree Fixes This Either

Iowa State University Extension is blunt about the tree end of it. There are no effective management solutions, and there is little that is practical other than tolerating the occasional annoyance. Spraying before the galls form is sometimes suggested, but Iowa State notes that several applications would generally be needed to make a noticeable difference, and that the galls do not harm the tree in the first place.

Nebraska Extension does not recommend insecticide for this at all, and offers hosing the siding down with water to anyone who cannot stand to do nothing. That is the honest shape of it: a tree insect having a two or three week moment, with the useful work sitting on the building rather than on the insect.

The Gaps Letting Them In Are Carrying Other Things

This is the part worth acting on, because a psyllid is the smallest thing testing your house this month and nowhere near the most serious. That sun facing wall, that window frame gap and that tired garage door sweep are also the route for the insects that do settle in, and for mice. Our State Shield Essential plan runs four visits a year, timed to break egg cycles rather than to chase a sighting, and covers ants, spiders, millipedes, centipedes, cockroaches, mice, rats, bees, wasps and seasonal invaders. If pests come back between treatments, so do we, at no cost. Nobody treats a hackberry psyllid, but the October walk around a house is the same walk either way.

• Start with the windows you open. Minnesota aims 18 mesh screening and a storm window at exactly this insect, and the windows nobody opens are already doing their part.
• Caulk the frames rather than the glass. Ohio State puts gaps around door and window frames on its fall invader list, and that is the route for anything that did not come through the mesh.
• Look at the garage door sweep. Ohio State names worn sweeps specifically, and it is the same gap a mouse uses in November.
• Check the siding for damage while the ladder is still pleasant. Same list, same reason, and it gets harder to want in December.
• Vacuum what is already inside. Nebraska says to seal the bag and get rid of it right away rather than leaving it in the closet.

When It Is Not Coming Through The Screen At All

Several other things turn up on Ohio windows in the same weeks and none of them is a psyllid. A dark red speck that smears, something that jumps, or a pale crawler near damp cardboard is the windowsill group, sorted out in our post on the tiny bugs on your windowsill. Something bigger and slower massing on the south wall is a boxelder bug or another fall invader. Sluggish flies on the glass on a mild winter afternoon are usually cluster flies coming out of a wall void. Small dark flies walking on the soil of a houseplant never came through the screen at all, and the small flies in an Ohio kitchen guide covers where those breed.

State Termite has been working on Stark and Summit County houses since 1933, from the office on South Main Street in North Canton and a second one in Hartville. If something tiny is getting into your house and you cannot tell whether it matters, get a free estimate or call 330-494-6199 and describe what the window looks like. All treatments are pet safe and kid safe, and you usually do not need to be home unless a technician needs interior access.