# Why don't spiders starve? **URL:** \ **Category:** Factual Questions\ **Created:** [July 15, 2004, 8:07pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314 "2004-07-15T20:07:17Z")\ **Posts on this page:** 20\ **Page:** 1
**Author:** ![Genghis\_Bob](https://avatars.discourse-cdn.com/v4/letter/g/45deac/32.png) [@Genghis\_Bob](https://boards.straightdope.com/u/Genghis_Bob)\ **Post date:** [July 15, 2004, 8:07pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/1 "2004-07-15T20:07:17Z")
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: 1. Something about their eyes. Bug eyes just aren’t set up correctly to see the strands? 2. 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? ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [July 15, 2004, 8:24pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/2 "2004-07-15T20:24:14Z")
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. ---
**Author:** ![brane\_damaj](https://avatars.discourse-cdn.com/v4/letter/b/a587f6/32.png) [@brane\_damaj](https://boards.straightdope.com/u/brane_damaj)\ **Post date:** [July 15, 2004, 8:40pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/3 "2004-07-15T20:40:23Z")
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. ---
**Author:** ![AndrewL](https://avatars.discourse-cdn.com/v4/letter/a/3d9bf3/32.png) [@AndrewL](https://boards.straightdope.com/u/AndrewL)\ **Post date:** [July 15, 2004, 8:46pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/4 "2004-07-15T20:46:56Z")
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. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [July 15, 2004, 10:17pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/5 "2004-07-15T22:17:58Z")
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. ---
**Author:** ![Thaumaturge](https://avatars.discourse-cdn.com/v4/letter/t/858c86/32.png) [@Thaumaturge](https://boards.straightdope.com/u/Thaumaturge)\ **Post date:** [July 15, 2004, 10:28pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/6 "2004-07-15T22:28:53Z")
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. ---
**Author:** ![Thaumaturge](https://avatars.discourse-cdn.com/v4/letter/t/858c86/32.png) [@Thaumaturge](https://boards.straightdope.com/u/Thaumaturge)\ **Post date:** [July 15, 2004, 10:35pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/7 "2004-07-15T22:35:21Z")
Here’s one [cite](http://www.xs4all.nl/~ednieuw/australian/araneidae/araneidae.html) that has a spider using its web to attract pollinating insects. > [@](#): > > The spiders of this family are easily identified by the zig zag silk construction (stabilimentum), usually a cross, they make in their web. It is believed that the spider uses it to camouflage itself in the cross and to warn birds not to fly through the web. > But there are also other hypotheses. > Perhaps the most important function of stabilimenta is to attract insects. The silk of the stabilimentum reflects UV light and pollinating insects are lured to these threads. Here’s another [one](http://www.abc.net.au/science/scribblygum/february2004/): > [@](#): > > These thick silky crosses reflect a large amount of UV light, the wavelength of light insects use to guide their movements. Many flowers also reflect UV light, alerting insects to their presence. Marie Herberstein from Macquarie University says insects may perceive the cross as breaks in the foliage - escape routes marked by light which they automatically fly towards - and in doing so, fly straight into the spider’s trap. ---
**Author:** ![astro](https://avatars.discourse-cdn.com/v4/letter/a/9dc877/32.png) [@astro](https://boards.straightdope.com/u/astro)\ **Post date:** [July 15, 2004, 10:45pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/8 "2004-07-15T22:45:08Z")
[ULTRAVIOLET REFLECTANCE OF SPIDERS AND THEIR WEBS](http://www.americanarachnology.org/JoA_Congress/JoA_v30_n2/arac-30-02-246.pdf) Some notes. It does reflect UV per T-urges note. ---
**Author:** ![Dog80](https://avatars.discourse-cdn.com/v4/letter/d/6bbea6/32.png) [@Dog80](https://boards.straightdope.com/u/Dog80)\ **Post date:** [July 15, 2004, 10:57pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/9 "2004-07-15T22:57:39Z")
Shouldn’t flies have evolved better vision by now? (to avoid webs) ---
**Author:** ![Thaumaturge](https://avatars.discourse-cdn.com/v4/letter/t/858c86/32.png) [@Thaumaturge](https://boards.straightdope.com/u/Thaumaturge)\ **Post date:** [July 15, 2004, 11:22pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/10 "2004-07-15T23:22:18Z")
I guess in an evolutionary sense, being able to fly through trees and bushes and find flowers is more important than being able to avoid spiderwebs. ---
**Author:** ![RealityChuck](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/realitychuck/32/195_2.png) [@RealityChuck](https://boards.straightdope.com/u/RealityChuck)\ **Post date:** [July 16, 2004, 12:19am UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/11 "2004-07-16T00:19:46Z")
> [@Dog80](#): > > Shouldn’t flies have evolved better vision by now? (to avoid webs) 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. ---
**Author:** ![great\_glowing\_balls\_of\_jelly](https://avatars.discourse-cdn.com/v4/letter/g/67e7ee/32.png) [@great\_glowing\_balls\_of\_jelly](https://boards.straightdope.com/u/great_glowing_balls_of_jelly)\ **Post date:** [July 16, 2004, 12:46am UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/12 "2004-07-16T00:46:26Z")
> [@RealityChuck](#): > > 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. ,but the ones that did manage to avoid the webs would breed more. ---
**Author:** ![Thaumaturge](https://avatars.discourse-cdn.com/v4/letter/t/858c86/32.png) [@Thaumaturge](https://boards.straightdope.com/u/Thaumaturge)\ **Post date:** [July 16, 2004, 1:00am UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/13 "2004-07-16T01:00:07Z")
…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. ---
**Author:** ![Thaumaturge](https://avatars.discourse-cdn.com/v4/letter/t/858c86/32.png) [@Thaumaturge](https://boards.straightdope.com/u/Thaumaturge)\ **Post date:** [July 16, 2004, 1:08am UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/14 "2004-07-16T01:08:24Z")
err that should be _flies_…flying into **trees**. ---
**Author:** ![BoringDad](https://avatars.discourse-cdn.com/v4/letter/b/ad7895/32.png) [@BoringDad](https://boards.straightdope.com/u/BoringDad)\ **Post date:** [July 16, 2004, 4:08am UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/15 "2004-07-16T04:08:41Z")
> [@Dog80](#): > > Shouldn’t flies have evolved better vision by now? (to avoid webs) 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. ---
**Author:** ![David\_Simmons](https://avatars.discourse-cdn.com/v4/letter/d/9de053/32.png) [@David\_Simmons](https://boards.straightdope.com/u/David_Simmons)\ **Post date:** [July 16, 2004, 4:30am UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/16 "2004-07-16T04:30:28Z")
> [@Dog80](#): > > Shouldn’t flies have evolved better vision by now? (to avoid webs) 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. ---
**Author:** ![Smeghead](https://avatars.discourse-cdn.com/v4/letter/s/f1d935/32.png) [@Smeghead](https://boards.straightdope.com/u/Smeghead)\ **Post date:** [July 16, 2004, 5:38am UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/17 "2004-07-16T05:38:01Z")
> [@David Simmons](#): > > 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. ---
**Author:** ![BoringDad](https://avatars.discourse-cdn.com/v4/letter/b/ad7895/32.png) [@BoringDad](https://boards.straightdope.com/u/BoringDad)\ **Post date:** [July 16, 2004, 7:34pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/18 "2004-07-16T19:34:14Z")
> [@Smeghead](#): > > 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. ---
**Author:** ![CC](https://avatars.discourse-cdn.com/v4/letter/c/f1d935/32.png) [@CC](https://boards.straightdope.com/u/CC)\ **Post date:** [July 16, 2004, 7:39pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/19 "2004-07-16T19:39:59Z")
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. ---
**Author:** ![brane\_damaj](https://avatars.discourse-cdn.com/v4/letter/b/a587f6/32.png) [@brane\_damaj](https://boards.straightdope.com/u/brane_damaj)\ **Post date:** [July 19, 2004, 1:42pm UTC](https://boards.straightdope.com/t/why-dont-spiders-starve/255314/20 "2004-07-19T13:42:24Z")
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. [Next page](https://boards.straightdope.com/t/why-dont-spiders-starve/255314.md?page=2)