Man made lighting is a very new thing. Electric lights are only about 150 years old, even gas mantle lights are not too much older. Before that it was torches. And I would expect that the heat they generate would deter a spider from going too close to it. More importantly, why would they ever? I can’t imagine a spider’s web building instinct would have ever included being attracted to lights in the dark (because until recently there weren’t any!)
I know that evolution is an agonizingly slow process, yet I can’t help but think that spider webs built in front of outdoor lights is a ‘common’ thing. They also always seem like a pretty successful place to build one. If it isn’t evolution, how would you describe it such recent seemingly ‘learned’ behavior? Is it just flawed observational logic?
Spiders build webs where there are plenty of bugs. Bugs are attracted to lights. I’m guess that the spiders are attracted by the bugs rather than by the lights.
There’s a lot more light out there when there’s less light out there. By which I mean, without artificial light, there’s still a surprising amount of natural light, more than you can really notice with light pollution. Bugs have been attracted to light for longer than we’ve been making it. (So have baby sea turtles…they crawl toward the lighter patch in the night, which was the sea until we came asking and screwed that up; now they often get lost crawling towards the lights of land.) So it’s possible spiders have been spinning webs in open areas because that’s where they catch bugs, and before people came along, the proxy for “open space” was “that looks lighter over there…”
But also, don’t underestimate the speed of evolution under certain circumstances. Natural selection very rapidly favored the moths in early industrial cities that happened to look like soot, changing the typical specimen of the species within a single human generation. If a mutation is very, very advantageous in the creature’s environment, selection can happen pretty quickly. And since spider food loves light so much, favoring lighted areas for spinning a web is a fantastic quirk that could be rewarded with many fat babies.
I kind of doubt that spiders survey the room and say “aha! The bugs are over by the light, I think I’ll build my web there.”
I recall from some previous threads that baby spiders more or less are blown by the wind and build their webs wherever they end up. If they end up where bugs are, they thrive. If they end up where no bugs are, they die. But they have lots of babies to make up for it.
What you may be seeing is simply that when a spider by chance builds a web near a light, it lives long, prospers, and has many babies in the vicinity. A spider who by chance builds a web elsewhere soon starves to death (because all the food is hanging around the light) and doesn’t maintain its web.
If there is in fact any bias of there being more spider webs near artificial lights I would guess that this is the cause. Spiders that build webs in areas with lots of flying bugs environments stay there and survive; those that build in non-productive areas either move to more productive ones or die. So any effect is probably mainly behavioral rather than genetic.
Many other nocturnal insect-eating animals have learned to exploit artificial lights, including bats, owls, toads, and geckos. And some day-foraging birds will go around just after dawn collecting insects that were attracted to lights at night.
In addition to natural or visible light I find that spiders frequently will spin across my infra-red security cameras, which insects also are attracted to at night. Not sure which came first, the flying insects or the spiders but the phenomenon does appear to be ‘multi-spectrum.’ It happens frequently enough that I often have to pass a dustbroom past the lens to clear them and prevent their trigger of motion-sensing recording.
I have spent years watching spiders close up and personal. Tracking the webs on the glass doors which attracted insects to the kitchen light indicated that small spiders would often sit on the edge of the web of larger spiders. These were Australian black house spiders (Badumna insignis), but they have the same niche as the funnelled-web spiders of other continents.
The little spiders would move into the web when the older spider died, usually because it was taken by the birds who seemed to think my webs were there for their smorgasbord pleasures. Over the years, those webs grew much bigger than webs of less successful spiders. I wonder how much the webs of previous spiders are exploited by little guys who land nearby. The silks from older webs can extend to quite a large (relatively) area to be detected by the spiderlings.
When we sold the house, five years of webs had to be removed from the windows. I was devastated. But we did carefully twist them onto sticks. The spiders will stay with their webs and we could relocate the remaining residents. Nothing like obsession, is there?