Why Boxelder Bugs and Lady Beetles Cover Your Windows in Fall

Boxelder bugs and lady beetles pile up on windows in fall because the south and west walls of the house hold the afternoon sun. Once the sun comes off the wall they start looking for a gap to spend the winter in, and window frames and storm window tracks are the first gaps they find. Neither insect damages the house and neither one breeds indoors. The real problem is that if you squash them on the glass, they leave a stain that is harder to deal with than the bugs were.

Why they end up on the windows

Boxelder bugs are the flat black ones with red or orange lines down the back. They spend the summer feeding on boxelder, maple and ash seeds, which describes most of the boulevard in the older parts of Saint Paul and Minneapolis. You do not need a boxelder in your own yard for this. A seed heavy silver maple two houses down is plenty.

Asian lady beetles are the orange ones. The spot count varies, which is why people argue about whether they are real ladybugs. They are not native, and they are the ones that get into houses here. Our native ladybugs mostly overwinter outside in leaf litter and stay out of your living room.

Both do the same thing in October. They gather on warm vertical surfaces in the afternoon, which means light colored siding facing south or west, and then they work toward any crack that leads somewhere sheltered. Around a window that is the gap where the trim meets the siding, the tracks and weep holes on an old aluminum storm window, a torn screen corner, or a sash that no longer seals.

Do not squash them on the glass

This is the part worth remembering. Asian lady beetles do something called reflex bleeding when they are threatened or crushed. They release a yellow fluid that smells bad and stains, and on glass, painted trim and light upholstery it sets in. Boxelder bugs leave a reddish smear and a smell of their own.

So a window full of bugs is a nuisance. A window full of smashed bugs is a cleaning job. A rolled up newspaper is the wrong tool here.

How to get them off

Vacuum them. A shop vac or a hose attachment lifts them off siding, screens and window tracks without crushing anything. Empty it outside right away, or drop a knee high nylon stocking into the hose first so the bugs collect in that and never reach the canister. If they sit in the vacuum, it will smell.

For clusters on siding out of reach, plain soapy water in a pump sprayer kills them on contact and rinses off. Dish soap and water is enough. You do not need a product for this.

Inside the house, vacuum and let it go. They are not laying eggs in your walls and they are not eating anything. The ones that trickle out of a window frame in February are leftovers from October, not a new generation.

The fix is caulk and screens, not spray

Barrier sprays on the outside of a house help some, wear off fast, and do nothing about the bugs already behind the siding. What works is closing the openings before it gets cold.

• Walk the south and west sides and caulk where the trim meets the siding
• Seal around window and door frames, and where utility lines pass through the wall
• Check that screens still seal in their frames and that no corner has pulled loose, since a bad screen corner is an open door
• On old aluminum triple track storms, clear the weep holes at the bottom of the frame with a paperclip

That last one is good practice anyway. Plugged weep holes are what rots a sill on these older Twin Cities houses, and clearing them takes away a spot the bugs like to sit in. October is the month for all of it. Once the wall is cold the bugs have already picked their spot, and once they are inside the wall cavity there is not much to do but vacuum them up as they appear.

Where window cleaning comes into it

Most of this is a Saturday with a caulk gun and a vacuum, and you do not need to hire anyone for it. Where it turns into a cleaning job is afterward: the yellow spotting left on glass and trim, the gritty mix of dead bugs and dirt that collects in storm window tracks and sills, and the screens that have been holding all of it against the house since September. Pulling and washing the screens is worth doing in the same trip, and it is the right time of year for it either way. More on that in cleaning and storing screens before winter.

If the exteriors need doing before the weather closes, we clean windows in St. Paul, Minneapolis and the surrounding suburbs, tracks and sills included. Here is more on our window cleaning service. You can request a free quote or book a free 10-minute consultation.