No way to know.
But think about this. Once upon a time there were no incandescent lights, but spiders were successfully surviving. Then, humans invented incandescent lights, and spiders started building webs by the lights, in order to catch moths and bugs attracted by the light. Since the spiders have no apparenct way of teaching each other, how did they learn that “trick”? Amazing.

Where the bugs are. That’s my guess. Of course, I’m not a spider. But I do play one on TV. ;-)

I’ve recently discovered several in rooms that get little to no activity. All are near windows. Time to start cleaning more thoroughly.

Most animals in general follow the food source. I am assuming that they try a couple places out and stick with area of “high income” ^.^

I guess the simple answer to :What determines where spiders spin their webs?” is…Spiders. Natural selection has equipped them with a built0in understanding of where dugs they wish to catch are likely to fly, and where there are sufficiently close objects to allow web construction. With their many eyes, they search out the best spots. It’s pretty amazing.

Consider the fact that something with a brain no larger than a housefly can see a hand coming to swat it and take off before you can smush the critter. Once airborne, it can change flight direction so rapidly it is nearly impossible for even the fastest human to snatch the fly out of the air. They can even fly up to the ceiling, do a 180% barrel roll and land unside down, sitting on the ceiling laughing at our puny efforts to overpower them even though their brain is no larger thanthe anger0narrowed pupil of one of our eyes.

Wherever I’m planning to walk, at face level.

@Pied_Pfeffer , You make a good point. Animals tend to be drawn to light, so windows are in general a good location for webs, but not the only one. I knew someone who raised horses. Horses attract a lot of flies and these attracted lots of spiders. A regular activity was to clear out the cobwebs from the horses’ windowless stalls..

I wonder if spiders ever abandon a web and make another one somewhere else. Given the time and energy invested in making a web and the short lifespan of most spiders, that would not be a move that could be made very many times.

@zophu Isn’t that Spider 101? I’ve made the same observations. It’s usually an area with a light breeze to a blowing gale, at least at our place and the places I’ve lived in.

When I’ve ever cleared cob webs away they’re back again later that night for the evening food rush of flying creatures.

They are incredible.

I do not believe it matters.
Unlike larger animals that follow a certain migration path. So, it is best for the “hunter” to find these paths and then sit and wait.

There are literally thousands of bugs in your back yard or traveling through it in a given day.
Any place a spider sets up shop will be a good place.

I know there are types of spiders that take advantage of sunlight, reflecting it with their webs to make bugs easier to catch.