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Why do spiders have 8 eyes?

8 eyes are cool. You have a couple of eyes that zoom in forward dedicated to stereoscopic vision for hunting, and six other eyes so you can look everywhere else and avoid getting eaten or squashed by a rolled up newspaper yourself.

This way you have complete control of the situation without moving your head (which they probably can't do anyway) or body and thus reveal your location to predators or prey who notice movement easily.

So why exactly eight? 6 or 10 would probably work, too. Because of basic mirror symmetry built into our genes since we were all pathetic little worms a few hundred million years ago, most organs come in pairs, so 8 is four pairs.

8 probably gives better 360 degrees coverage than 6, and going up to 10 is probably not worth the extra hassle, so natural selection settles for 8.

Ririon (Not a biologist)
 
I read somewhere that scorpions can have up to 12 eyes. Maybe it was that "Eye Designe" page.
 
What about the fact that spiders sit on a web waiting for anything to pass by and can't move, or the prey will not step on the web? Don't all spiders hunt by remaining absolutely still and waiting - ie ambush?
 
Of course, if 6 would do instead of 8, or 12, then this is an example of unintelligent design.
There again, maybe God gives them a few spare in case they lose a some (Isn't that why we have 2 lungs and 2 kidneys?).:)
 
IllegalArgument said:
I had a had feeling it might be an ID site, but it had a good description of spider eyes. So, I let it pass.
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The information itself is pretty good, but the subtle (and constant) use of the word 'design' and implication of intent made me grown inside.

Athon
 
Hydrogen Cyanide said:
We don't have many of those here. Perhaps because of the 3" wide Giant House Spiders: http://www.zoo.org/educate/fact_sheets/spiders/giant.html

Occasionally one (or one of its smaller cousins, like the Hobo Spider) will take up residence on the den ceiling. We then call it "Fred" our pet spider.

Once in a while a kid will get freaked out by one (usually if it is on the wall above their bed). That's when I get out the vacuum cleaner and suck it up (and that is a good opportunity to clear up some cob-webs in the corners).
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Gaah! Remind me never to visit the Northwest. Holy crap.

(Why the heck am I reading this thread?!?)
 
CBL4 said:
My guess it is related to their 8 legs. Whatever gene(s) cause 8 legs also caused 8 eyes. All the legs and all the eyes are on the same part of the body (Cephalothorax the front of the two body sections). I could easily be wrong but it's my hypothesis.
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IIRC, not all spiders have 8 eyes. I believe spiders may have 4, 6, or 8 eyes.
 
athon said:
The information itself is pretty good, but the subtle (and constant) use of the word 'design' and implication of intent made me grown inside.

Athon
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Please, sir! Was that a typo? Or are you some sort of malformed wierdo?

(I appreciate the two need not be mutually exclusive.):D
 
patnray said:
IIRC, not all spiders have 8 eyes. I believe spiders may have 4, 6, or 8 eyes.
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Somewhere I heard there are even spiders with no eyes at all. Anyone know about those?
 
Ipecac said:
Gaah! Remind me never to visit the Northwest. Holy crap.

(Why the heck am I reading this thread?!?)
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I once remember reading that some celebrity had moved here because he had heard the climate was nice, pretty scenery and lack of bugs --- then he found out that the lack of certain bugs were because of the spiders were big enough to carry off his young son.

:D

Fortunately, there are no scorpians. There were 3" long scorpians in our house in Texas. One stung my dad on the nose while he was in bed... though considering the size of his nose it was a BIG target! I used to pick up the scorpians with the barbecue tongs and put them down the garbage disposer.
 
Originally posted by patnray
IIRC, not all spiders have 8 eyes. I believe spiders may have 4, 6, or 8 eyes.
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I discovered that while trying to see if my prediction about correlation between legs and eyes was correct. It is evidence of my hypothesis being wrong but from what I know about bug development, it is not very strong evidence. It is possible to have a repressor gene that would prevent the expression of the eye genes in certain location.

Unfortunately, I could not find any information about spider mutation causing different number of legs. I think that would much stronger evidence.

BTW, the fact that spider eyes are frequently in two rows of four makes me think I am probably wrong. I was assuming that each side had four eyes in row just like their legs. A different configuration makes it more likely that there is no genetic correspondence.

Oh well, if you see a six legged spider, count the eyes for me.

CBL
 
My conjecture after reading the article, would be that each pair of spider eyes serve a single or small number of functions. One set to watch the web, one set to watch for attackers, and so on. Where as insect eyes tend to be multi-task organs.

Just my WAG.
 
Better range of vision, like compound eyes only not as complex.

Anyway that's what I was told in the fourth grade. There's probably a lot more going on.
 
Deetee said:
Just wondering...
What are the possible evolutionary reasons/benefits? Is there a specific different function for some of these?
Most (if not all) seem to be on the front of the head and primed for binocular vision, but how many does a spider need before redundancy creeps in?
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:con2: Spiders obviously have the power-of-two symmetry thing going on. I don't know if anybody has done a serious study of spider embryology (probably so), but I'd be willing to bet that in early stages there's one per leg, and they migrate.
 
It's so spiders can be even cooler than they already are >.>

Although I can see how having eight eyes would help when you can't turn your head. It would give them both hunter's vision AND the ability to see all around them.


...my brain now hurts from trying to imagine what it would be like.
 
Soapy Sam said:
Please, sir! Was that a typo? Or are you some sort of malformed wierdo?

(I appreciate the two need not be mutually exclusive.):D
Click to expand...


Yes. To both.

My malformed twin inside is also nodding.

Athon
(I noticed the typo too late to change it. Now I think it looks better as it is. If I grown inside, it's because God designed me that way)
 
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