Fall Invaders in Western NY: Stink Bugs, Cluster Flies and Boxelder Bugs
On a warm October afternoon in Western New York, you might see dozens of insects on the sunny side of your house. A few weeks later, some of them show up on windows inside. These are "overwintering" pests, and they follow a predictable yearly pattern.
Why do these bugs come inside in the fall?
These insects survive winter by finding a sheltered spot and staying inactive until spring. In nature, that might be under tree bark or in leaf litter. Houses offer plenty of protected spaces: wall voids, attics, gaps behind siding and window frames.
They gather on the warmest, sunniest walls, usually south and west-facing, in late summer and early fall. Then they crawl into any gap they can find. On warm winter days, or when your heat comes on, some get confused and wander into living spaces.
What do stink bugs, cluster flies and boxelder bugs look like?
| Insect | Look | Notes |
|---|---|---|
| Brown marmorated stink bug | Shield-shaped, mottled brown, about 5/8 inch, light bands on antennae | Releases an unpleasant odor when disturbed or crushed |
| Cluster fly | Slightly larger than a house fly, dark gray, slow and sluggish, golden hairs on the thorax | Larvae develop in earthworms in lawns; adults gather in attics and upper rooms |
| Boxelder bug | About 1/2 inch, black with red or orange lines | Often near boxelder and maple trees; can leave small stains |
Penn State Extension has a detailed fact sheet on the brown marmorated stink bug, and Cornell IPM's cluster fly guidance covers that pest as part of the NYS IPM program.
Do these bugs cause damage or breed in my house?
They're nuisance pests. They don't breed indoors over the winter, they don't eat your food or wood, and they don't damage your home's structure. Boxelder bugs and stink bugs can leave small stains, and stink bugs smell when crushed. Large numbers of cluster flies in an attic can attract other pests when they die.
How do I keep fall invaders out of my house?
Sealing is the most important step. Focus on the sunny sides of the house and upper floors:
- Seal gaps around windows, doors, siding, fascia and utility penetrations with good-quality caulk.
- Repair and fit screens on windows, attic vents and soffit vents.
- Install or replace door sweeps and weather stripping.
- Screen gable and ridge vents with fine mesh.
- Cap chimneys and check gaps where the chimney meets the house.
- Check window air conditioners, which leave gaps around the frame.
Older homes in Western New York often have many small gaps, so it's normal for sealing to reduce, but not completely stop, these insects.
When is the best time to treat for fall invaders?
Late summer, before they move in. In Western New York, that usually means late August through September, before insects start gathering on the house. Once they're inside the walls, treating is far less effective.
A professional exterior treatment, applied to the sunny sides of the house and around common entry points according to the label, can reduce the number that make it inside. Combined with sealing, it gives the best results.
Should I crush or vacuum the bugs that get inside?
Vacuum them. Crushing stink bugs releases their odor, and crushing boxelder bugs can leave stains. A vacuum with a disposable bag, or a shop vacuum you empty outside, works well. Some people keep a dedicated old vacuum just for this in the fall.
You can also knock them into a container of soapy water.
What doesn't work against fall invaders?
- Spraying insecticide inside the walls in winter. It often kills insects that then attract carpet beetles and other scavengers, and it doesn't stop more from coming out.
- Bug bombs or foggers. They don't reach insects hiding in wall voids.
- Sealing interior gaps only. Outlets and baseboards help keep insects out of living spaces, but the real work is on the outside.
- Waiting until December. By then, the insects are already inside.
Fall invader FAQs
Why are there so many flies in my upstairs windows?
Slow, sluggish flies gathering in upper windows and attics in fall and early spring are usually cluster flies. They overwinter in attics and wall voids and come out on warm days.
Are stink bugs harmful to people or pets?
Stink bugs don't bite or sting, and they're considered a nuisance pest. Their main problem is the odor they release when disturbed.
How do I get rid of boxelder bugs on my house?
Seal gaps on the sunny sides of the house and consider a late-summer exterior treatment. Spraying them with soapy water outside can help with clusters you can reach.
Will these bugs go away on their own?
They'll leave the house in spring to go back outside. The same house tends to attract them again each fall unless gaps are sealed.
Can you get rid of all of them?
It's hard to fully eliminate fall invaders, especially in older homes. Sealing and a timely exterior treatment can greatly reduce how many get inside.
Get ahead of fall invaders this year
Gernatt Pest Solutions helps Western New York homeowners seal up and plan exterior treatments before fall invaders move in. Our technician holds dual NYSDEC 7A and 7F certification, and estimates are free.
Call (716) 605-5676 or email info@gernattpestsolutions.com.