Let’s focus on those spiders who catch their prey by stringing a web and waiting for somebody to stumble or fly into it.
Now, I’m a lot bigger than the average bug, especially in relation to the web. And I can see the darned thing. So why can’t they? How can they not avoid a structure that must look like it’s made of construction cables to them? I can hazard a couple of guesses:
Something about their eyes. Bug eyes just aren’t set up correctly to see the strands?
Lack of experience. The first time a bug sees a web is usually their last?
On a not-very-related note, how thick would a spider web have to be, to be strong enough to hold an average adult human? And how big would the spider have to be, to spin it?
as to your last question, spider silk is much stronger than steel. how thick a steel cable would you need to hold up a person? Not very. In the millimeters, I’m guessing.
It all boils down to one thing: Flies aren’t very smart.
I’m not at all sure that flies can see the Web at all, because their vision simply isn’t as good as ours is. The thin strands of spider web could easily get lost in their blurry vision.
But, even if they could see perfectly, they wouldn’t necessarily know to avoid them. I can see a fly saying to himself, “Say, I think I’ll take a rest on some of these strings that someone left dangling right here. Gosh, they sure are sticky…” After all, the retards never seem to catch on to the fact that the window is an impassable barrier…
I was also told years ago that flies use air currents to help them navigate around obstacles, and since air goes right through a Web, they’d fly right into it. I cant’ be certain if that’s completely accurate, though.
As a human, you have vision which is better than that of nearly any other creature on the planet. A fly doesn’t see anywhere near as well as we do. They can see about well enough to detect large, opaque objects. Thin translucent strands are pretty much impossible for them to see until it’s too late.
Some fairly sophisticated studies have been done of insect vision and IIRC spider silk is effectively invisible within the range of reflected radiation that insects fairly simple eyes can typically see within, and especially in the upper UV range. It’s more or less invisible there.
Funny, I remember the exact opposte, astro, that the web is more reflective in the UV range, which misleads the insect into thinking it is part of the sky. I’ll see if I can dig up something.
Why? The species seems to be doing all right with its current arrangement. Not enough flies get eaten by spiders for the better vision to be necessary.
…unless the ones that managed to avoid webs did so entirely by blind luck and no skill of their own. Entirely possible for a creature that can spend an entire day trying to fly through a window to have little skill.
Maybe the flys that have expressed a mutation for decreased sensitivity for ultraviolet light can no longer find food and spend much time flying into, counterbalancing their new immunity to being lured into spider-webs.
Better eyes would be bigger, which comes with its own pitfalls in a creature so tiny.
That’s like asking “Shouldn’t dogs have evolved 10” fangs by now?" Animals don’t get to choose what new features they get. Obviously no fly was born with a web avoiding mechanism that it could pass on to it’s offspring. Sure, maybe it would be a great fly life enhancer, but if that mutation never arises, it can’t be passed on.
Not necessarily. Flies reproduce rapidly and spider webs don’t really catch all that many so they have little or no effect on species survivial. Of course that doesn’t help the individuals, but I can’t get too worked up about a fly.
Additionally, vision that was better adapted to see spiderwebs would have an associated cost of some sort - maybe it’d be less able to see potential food sources, or maybe it would just simply take more energy to grow that kind of eye. You’d need a mutation that would provide a benefit greater than whatever cost is associated for it to really provide an overall advantage.
Plus, spiders and flies are both evolving simultaneously. If one comes up with a new trick, odds are it won’t be long (on an evolutionary scale) before the other one comes up with a countertrick.
It is very misleading to phrase it that way. Do you perhaps mean that if flies no longer landed in webs, the spiders that catch their prey in other ways will come to dominate the world of spiders? After all, animals do not “come up with” tricks through evolution. Evolution just weeds out the animals that survive the best.
well, if we’re phrasing things more precisely, do we want to say that “nature weeds OUT the animals that survive the best”? It might be better to suggest that nature weeds out those species that don’t survive. Of course, survival is defined as the avoidance of being one who is weeded out. Hmm. Ok, next good hitter, take a swing.
BTW: Just for the sake of info, at least some breeds of spiders can live for two years without food. I read about a fellow who starved a southwestern species of tarantula (probably Aphonopelma genus), and it lived for two years. Hardly scientific, I know, but it at least gives us a ball park idea of how long a spider can afford to wait before a fly stumbles into its web.