There are many insects which you may see at home at this time of the year. The insects most likely to be staging on outside walls and beginning to move into houses, garages, or wall spaces are boxelder bugs, cluster flies, conifer seed bugs, and Multi-colored Asian Lady Beetles. You may also find wasp species, other insects, and even spiders on these sunny spaces, but they will not usually move inside to hibernate, although they will explore open doors and windows. A great source of good photos of these species, with some information, is a presentation put together by PJ Liesch, UW Insect Diagnostician, and found at: https://fyi.extension.wisc.edu/wihortupdate/files/2016/08/Late-Season-Insects-WHU-PJL.pdf
The hibernating insects move onto and into homes for one reason, survival. They hibernate in large colonies which allow them to survive the winter, as communal heat is sufficient enough for most of them to make it through on their lowered winter metabolic rate. When the fall days reach critical day-lengths and/or critical low temperatures, these species start congregating on likely hibernation spots.
Common hibernation zones include wall spaces of older homes, underneath siding or insulation of any home, and properly-sized hollow logs. They can literally show up overnight or, more properly, over the course of a day. The Multi-colored Asian Beetles are especially prone to this, where you leave in the morning and come back in the afternoon to south and west exteriors crawling with them. On the outside of your house, they’re an annoyance for a few days or a week or two, depending on the weather. When they start coming out of your walls on nice, warm days in mid-winter and flying around your tv and oven, they’re an absolute nuisance.
To prevent finding a few dozen per day INSIDE your home this winter, you need to keep them OUTSIDE your home now. The only way to do that is to pest-proof your entire home. Pest-proofing means sealing your home against insect entry. It entails some detective work and usually a fair amount of actual work, but if you don’t do it right, you’ll still have these insects inside your home.
Things you need to do to pest-proof your home include: Caulking all spaces on the edges of your siding (tongue-and-groove siding is especially bad, as where it meets the corner boards there is a perfectly-sized entry spot). Inspecting all door and window frames and then filling any cracks into wall spaces. Placing fine-mesh screening on all vent areas. Sealing up the areas around pipe entry holes. Checking for cracks in the main foundation and where the foundation meets the rest of the structure. AND looking for any other possible entry points, remembering that these insects need only about a 1/8 inch hole or a 1/16 inch crack to get in.
Although pest-proofing is the ONLY way to deal with insect entry in the long-term (besides the fact that there are other benefits of doing this to your house), there are chemical insecticides that can be used to try to combat these problems. The key to remember when using any chemical is that they are not a cure-all and you will still have insects entering your home if you do not do a complete job, just as with pest-proofing.
If you do decide to use an insecticide in your battle with these insects, you need to use one that will work effectively at cooler temperatures, which eliminates most of the more commonly-used household insecticides. The best insecticide products to use for these situations are the synthetic pyrethroids, which will work at cooler temperatures. Specific products to look for include ones with active ingredients such as cypermethrin, permethrin, or cyfluthrin. They will work hopefully as a repellent, but will likely eliminate any individuals entering the spaces. Please note that it is recommended to spray a small area of the structure to test for potential staining prior to spraying a large area.
In case you are curious, the biology of these hibernating insects is fairly different. Boxelder bugs use their needle-like mouthparts to suck plant juices out of a variety of host species, particularly maple trees and developing maple seeds. They are known to cause damage on fall berries and occasionally on other plants. Additional information on them is at: https://hort.extension.wisc.edu/articles/boxelder-bug-boisea-trivittatus/ and the MN Extension version is at: https://extension.umn.edu/nuisance-insects/boxelder-bugs The other plant feeders are the conifer seed bugs, and these are also the largest and most odorous. They feed primarily on developing seeds of various conifer trees. If you crush one of these about one inch long, gray insects with your hand, the odor will stay on your skin for awhile. If interested, more information is at: https://hort.extension.wisc.edu/articles/western-conifer-seed-bug/
The cluster flies you find buzzing in your windows will go outside and lay their eggs in the soil next spring. Their young hatch into small larvae that are parasites of earthworms throughout their development. Find more information on this species at: https://cdn.shopify.com/s/files/1/0145/8808/4272/files/A2090.pdf
Multi-colored Asian Lady Beetles are the only beneficial insect of the three, as they do act like normal lady beetles during the growing season, happily munching away on local aphid populations. The average adult lady beetle eats about 10 aphids per day. The Wisconsin Extension factsheet on this species is found at: https://hort.extension.wisc.edu/articles/multicolored-asian-lady-beetle/ and this article has a bit more on their biology: https://uwm.edu/field-station/multicolored-asian-ladybug-family-coccinellidae/