MadSci Network: Zoology
Query:

Re: How can b. widow spiders have 8 eyes when we need a lot of brain for 2?

Date: Sat Apr 15 17:30:30 2000
Posted By: David Richman, Staff, Entomology, New Mexico State University,
Area of science: Zoology
ID: 955775471.Zo
Message:

Black widow eyes, while more numerous than those of humans, are much 
simpler than the human eye. These spiders are mostly active at night and 
thus they need eyes much less than humans do.  In fact, despite their 
larger number of eyes, most spiders have rather minimal vision compared to 
humans, most only being able to distinguish between light and dark and some 
degree of movement.   The exceptions are the jumping spiders (Salticidae), 
ogre-faced spiders(Deinopidae) and wolf spiders (Lycosidae), but in these 
cases the major part of the vision is in one pair of eyes, not in all 
eight. The number of receptors even in jumping spider eyes are not anywhere 
as high as in human eyes, being only around 1,000. Human eyes have over 100 
million individual receptor cells in the retina. Thus spiders do not need 
the massive visual processing brain structure that we need.

References:

Foelix, R. F. 1996. Biology of spiders. 2nd ed. Oxford University Press, 
New York.

How the Eye Works. http://www.lasereye.com/howeye.html




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