Is an October wasp in your Marshalltown house from a wall nest or a wintering queen?

The yard nests are winding down, the porch is quiet, and yet there is a wasp on the inside of the kitchen window again. Maybe it is the third one today. Maybe it is the first one since last weekend. That difference tells you which of two problems you have.

Where do wasps inside the house in October come from?

Almost always from one of two places. Either a yellow jacket colony is still alive inside a soffit or wall void and some of its workers are finding a way into the rooms, or a paper wasp queen crawled in to spend the winter. The first needs wasp nest removal in Marshalltown now. The second is not a nest at all and can wait for frost.

On a windowsill both read as a wasp, but they behave nothing alike. A colony in the wall is a working nest with a queen, a brood and a steady supply of workers until cold finally shuts it down. The wasps that slip indoors from it are lost workers that took a wrong turn through a gap around a light fixture, a bath fan or the attic hatch, and more will follow them for as long as the colony lives.

An overwintering queen is a single insect with no colony around her. She mated in late summer, left the nest she was raised in, and went looking for a dry, sheltered gap to sit out the cold. An older house offers plenty. She wandered too far into one and came out in a bedroom.

A handful every day at one window, or one slow wasp now and then?

Count for a few days. Several wasps a day, turning up at the same window or the same ceiling light, busiest on warm afternoons, point to a live colony in the wall or soffit behind that spot. One wasp at a time, days apart, slow and crawling more than flying, points to a queen settling in for the winter.

A few details sharpen the read:

• Where they show up. Workers from a wall nest come out near their way in, so the same room keeps getting them. Queens wander, and a sunny window in any room will do.
• How they move. A worker indoors flies hard at the glass and buzzes along the frame. A queen in October is often barely moving, walking up a curtain or sitting on the sill.
• Time of day. Colony traffic follows the sun and the warmth of the wall. A queen tends to appear when a room warms up, the furnace kicks on, or morning light hits the glass.
• Dead ones. Three or four dead wasps on a sill every morning is a colony. One dried-up wasp behind the blinds is probably a queen that never made it back into the wall.

If the count is climbing, or you find them on two floors at once, treat it as a colony until someone has looked.

How do you find a yellow jacket nest in a soffit or a wall from the yard?

Go out on a sunny day around midday and watch the side of the house nearest the room where the wasps keep appearing. Stand well back, at least the width of a driveway, and look for a steady line of wasps flying straight in and out of one gap. That entrance is the nest’s front door, and the nest sits in the void behind it.

The usual spots are where two parts of the house meet and do not quite close: a gap between the soffit and the fascia board, a corner where the eave turns, a seam in the siding, a split in the trim around an upstairs window. On the older two-story houses near downtown the soffits are tall and the gaps are far off the ground, so binoculars help more than a ladder. Never stand directly under the entrance, and do not lean a ladder against that wall to get a closer look.

This late in the year the traffic may be only a few wasps a minute. Wasps going in and coming out of the same gap, over and over, still mean a colony behind it. If you are weighing whether to deal with it this fall, our cost page lays out what wall-void nest removal costs.

Does the first hard freeze end a wall nest on its own?

Eventually. A hard freeze stops the workers and the colony dies back, and by then the new queens have already left. A nest inside a wall can outlast the ones in the yard, though, especially on a wall shared with a heated room, where the house keeps the void warmer than the open air.

That warmth is why some people still have wasps in a back bedroom after the neighbors’ ground nests have gone quiet.

Waiting it out can be a reasonable choice for a small colony high in a soffit of a room nobody uses. It is a poor one when the wasps are coming into a bedroom, a nursery, or the room of someone who reacts badly to stings. And before you reach for the caulk gun on that outside gap, read the yellow jacket notes on our wasp and hornet removal page, which cover why the entrance stays open while the colony is alive.

Once the colony is dead or treated, the paper comb inside the wall dries out where it sits. A yellow jacket queen starts her own nest in spring rather than moving back into it, but the sheltered void and the gap that led to it are still there, and a spot that suited one colony tends to draw the next.

Where do queens spend the winter in an older Marshalltown house?

Anywhere dry, still and out of the wind. In the older houses off Center Street and around the downtown square that means attics, gable vents with torn or missing screens, loose soffit boards, gaps behind siding, and the space between a window and its old storm window. Queens settle in alone or a few together, not in crowds.

That last point is the easy way to tell them from the boxelder bugs and lady beetles on the south wall. Those arrive as a crowd on the warm side of the house. Wasp queens arrive quietly, one here, one there, and nobody sees them go in.

The storm-window gap is the one people find first. Lift the inside sash on a bright day in late fall and a queen that was tucked into the track drops onto the sill, slow and stiff. Attic queens are found by whoever goes up for the holiday boxes, usually clinging to the underside of the roof boards near a vent or settled into the folds of whatever has been stored up there longest.

Will a queen in the house sting, and what brings them out in winter?

She can, but only when pressed. A queen in a warm room is drowsy and wants to be left alone. Stings happen when one is grabbed, stepped on with a bare foot, rolled onto in bed or caught in a fold of laundry or curtain. A heated room or a bright window draws her out of the wall or attic and into the house.

Between November and March that usually means the rooms next to the furnace run, a bedroom ceiling under the attic, or a window that takes full afternoon sun. She warms up enough to move, heads for the light, and ends up on the glass.

For one on a window, put a cup over her, slide a piece of stiff paper underneath, and carry her outside. A fly swatter on a window tends to miss on the first swing, and a bug bomb for one insect is a lot of chemical for no gain. A queen or two over a winter does not call for a treatment. If they are turning up every few days in the same room, that room has a gap to the attic or wall worth finding.

What gets sealed, and when, so spring does not start in the same soffit?

Seal after the colony is dead or treated and before April, which is when the queens that wintered in and around the house wake up for good. Close the gaps at the soffit and fascia, put new screen in the gable vents, and caulk the siding seams and trim splits you found while watching the traffic in October.

Sealing in November or December, after a freeze has ended any wall colony, closes next year’s openings without trapping live workers in the wall. Queens already tucked into the attic stay there until spring, and with the outside closed, some of them will wander toward the rooms instead.

So inside, look at the paths the wasps used to reach the living space: the gap around a ceiling light, the bath fan housing, the trim around the attic hatch. A bead of caulk or a foam gasket there keeps those queens in the attic.

In April a new queen picks a sheltered spot and starts a nest the size of a golf ball, often under an eave or in the angle of a gable. Spotting it then means one queen and a handful of cells. One on a high eave, or one that keeps getting rebuilt in the same corner, is worth having removed while it is that small.