I always think of early September as the time of year that the spiders start coming down the windows in the evenings. During the day they skulk in the corners of their webs but in the evening they move out onto their webs to await the flies and moths. I am not sure whether the spiders are using that fact that insects are attracted by the lights in windows: there do not seem to be noticably more spiders outside our living-room, which is usually well-lit, when compared to our bedrooms which are relatively rarely lit. However, I have seen lights in an underpass downtown that were completely covered by a mass of webs, studded with the bodies of snared insects as if the spiders were catching far more food than they could deal with. There the lights were fluorescent and were left on all night.