I thought spiders have poor vision - why do they have eight eyes?
2007-03-14 23:49:00 · 16 answers · asked by Lord Onion 4 in Science & Mathematics ➔ Zoology
Spiders usually have eight eyes (some have 6 or fewer), but few have good eyesight. Most are able to detect little more than light-dark intensity changes and rapid movement - enough to stimulate nocturnal web building, hunting or wandering activities, as well as to allow rapid reactions against daytime predators (e.g., by dropping from webs). Some spiders have median eyes that can detect polarised light and they use this ability to navigate while hunting. For most night-active spiders sight is unimportant compared with touch, vibration and taste stimuli.
For a few spiders good vision is vital for hunting and capturing prey and for recognising mates and rivals. They include the day active jumping spiders and flower spiders, and the wolf spiders and net-casting spiders, more often seen by twilight or later at night.
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Types of eyes
Eight eyes are typically placed in two rows, on the front of the carapace. The AME or direct eyes, differ markedly in structure from the other indirect eyes (ALE, PLE, PME). The direct eyes appear dark, whereas the indirect eyes usually have a layer of light reflecting crystals, the tapetum, behind the light sensitive retina, giving these eyes a silvery appearance. The tapetum increases visual sensitivity because light entering the light sensitive retinal cells is immediately reflected back through them, so intensifying the image. These indirect eyes are adapted for seeing at low light intensities and their lenses are often enlarged in spiders with good vision. Spider eye lenses are better than photographic lenses in terms of their image brightness (very low F-numbers). However, because most spider eye retinas have relatively coarse-grained mosaics of receptor cells, their resolution of these images is much poorer than in the human eye.
2007-03-14 23:52:13 · answer #1 · answered by Anonymous · 7⤊ 0⤋
I wish I could tell you the real reason why some spiders have eight eyes but I would say that they're nocturnal predators but some do trap in daylight and some daylight insects move about swiftly. The spider has to define it's sight.
2007-03-16 13:45:38 · answer #2 · answered by Anonymous · 0⤊ 0⤋
they dont some have six eyes. same reason a fly has thousands of eyes in the one. if they had one eye they would see in only 2 d and their eyesight would be poor. but with six or eight eyes they can build up a better picture of their surroundings making them better hunters.
2007-03-16 05:24:38 · answer #3 · answered by Anonymous · 0⤊ 0⤋
Does it? I thought a spider only has eight legs.
2007-03-15 06:56:57 · answer #4 · answered by St Harpy 6 · 0⤊ 1⤋
lynn1805 yes they do have 8 eyes so get ur facts right luv
because they are evil and were sent to terrify us
i hate the b u g g e r s
2007-03-15 06:56:26 · answer #5 · answered by ms vicci pollard 5 · 1⤊ 0⤋
They are predators and need accurate vision.
They have a set for ultra-violet.
A set for near and far and one set to give them accurate stereoscopic vision far accurate assessment of distance.
2007-03-15 06:56:57 · answer #6 · answered by Billy Butthead 7 · 1⤊ 0⤋
They have 8 eyes and the "spidey-sense". I presume they have 8 eyes for making their webs and stuff.
2007-03-15 06:54:38 · answer #7 · answered by Joe Bloggs 4 · 2⤊ 0⤋
They have to wink a lot, to get a date. Would you date a spider?
2007-03-15 07:25:11 · answer #8 · answered by Kes 7 · 3⤊ 0⤋
To look at their 8 legs!!
2007-03-15 06:52:16 · answer #9 · answered by isleofskye 5 · 1⤊ 0⤋
Because they would look silly with 2 :D
2007-03-15 06:51:27 · answer #10 · answered by ? 7 · 1⤊ 0⤋