Different insects have different ways of surviving the winter. Many adult insects die off when frost arrives, but leave eggs behind to start next year's population. Some migrate to warmer climates. Still others burrow in the leaf litter or hide under loose bark for protection from the cold. Unfortunately, your warm home may be irresistible to insects seeking shelter from the cold.
In the fall, you may see aggregations of insects on sunny sides of your home. As we lose the heat of summer, insects actively seek warmer places to spend their days. Box elder bugs, Asian multicolored lady beetles and brown marmorated stink bugs are well known for this sun-seeking behavior.
When the sun sinks lower in the sky and winter approaches, these insects begin looking for a more permanent shelter from the cold. Some insects use aggregation pheromones to spread the word about a preferred overwintering site. Once a few bugs find good shelter, they give off a chemical signal inviting others to join them.
If your home has vinyl siding, insects may gather underneath the siding, where they are protected from the elements and warmed by your home's heating. Any crack or crevice large enough for an insect to crawl through is an open invitation to come indoors. You may find them gathered around windows, as poorly caulked window frames allow easy entry into your home. Usually, home-invading insects stay inside your home's walls during the winter. But on the occasional sunny winter day, they may make their presence known by gathering on your walls or windows.
The sudden appearance of dozens, or even hundreds, of insects in your home may be alarming, but don't overreact. The lady beetles, stink bugs, and other shelter-seeking insects won't bite, won't infest your pantry, and won't do structural damage to your home. They're just waiting out the winter like the rest of us.
If you really can't stand the sight of bugs in your home, or they appear in such large numbers that you have to take action, don't squish them. Many of the insects that come indoors emit foul defensive odors when injured or threatened, and some even ooze liquids that can stain your walls and furnishings. There's no need to resort to chemical pesticides, either. Just grab your vacuum and use the hose attachment to suck up the offending pests. Be sure to remove the vacuum bag when you're done, and take it outside to the trash (preferably inside a sealed plastic garbage bag).
Want to keep insects and spiders out of your house? Read 15 Ways to Bug Proof Your Home.