This is an interesting question because there are many facets to it. We must consider how well spiders do in winter, where they find food during the winter months, and how secure the exterior of your home is. There is another point we must consider, but we'll cover that later.
First of all, spiders can do quite well in a St. Louis winter. The temperatures here rarely dip below 32 degrees for long periods of time. They are equipped with the ability to generate a chemical substance that prevents freezing. This ability to tolerate the cold can allow them to invade a home in the middle of winter.
The second fact to consider is food resources. If a spider can't find a meal, it will have to go dormant. And, since spiders eat insects that can't tolerate cold temperatures, they often go into warmed man-made structures to find a meal. That means most spiders will invade in the fall.
Of the common spiders we have in Missouri, the black widow and the brown recluse are the spiders we get the most questions about because they can inflict serious bite wounds. Let's address them for a moment. Are brown recluse spiders active in the winter? Yes. These spiders can do well in man-made structures.
How about those black widows, are they active in the winter? Not usually. Black widows prefer to be outside where it is harder for them to get a bite to eat in the winter. But, when a black widow does find its way into a desirable location within a man-made structure, it can be active. If you have a basement with a dirt floor or a crawl space under your home, you could have active black widows in that space during the winter months.
If you have gaps, holes, or cracks in your exterior, your home will always be at greater risk for spider infestations, no matter what season. Sealing those entry points will make your home more resistant to spiders and other pests.
Spider infestations drop during months when temperatures get into the 30s, but it is important to understand that spiders don't only come in through your exterior walls. They can hitchhike into your home. Spiders get into boxes and find their way into furniture. If someone brings items into your home from a home that has a spider infestation, they can be transferred to your home quite easily.