Multiple Eyes Provide Excellent Vision

two large eyes flanked by two smaller eyes on a brown jumping spider can be seen standing on a green leaf

Biological Strategy

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Sense Light (Visible Spectrum) From the Environment

Living systems constantly receive signals from their environment that help them survive. Light (in the visible spectrum) can come from other living systems (such as fireflies) or from non-living sources (such as the sun). Survival often depends on sensing and responding to challenges like low light conditions or light that has been altered in some way. Because basic survival is at stake, living systems must excel at meeting those challenges. A well-known phenomenon is how water bends light. A stork trying to catch a fish underwater can compensate for this bending effect so that when it strikes at the fish, it has a good chance of catching it.

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Arachnids

Class Arachnida (“spider”): Spiders, mites, ticks, scorpions

Arachnids get a bad reputation, but they play an important role in the ecosystem by controlling insect populations. Almost half of the species in the class are spiders, and most live in terrestrial environments. Unlike insects, most arachnids have two body sections: the cephalothorax, which is the head and thorax fused together, and the abdomen. Mites and ticks, on the other hand, have only one body section that is relatively flat. This body shape comes in handy for the species that are parasitic, because it makes it harder for their hosts to bite or scratch them off.

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The eight eyes of a jumping spider provide it with excellent vision via two principal eyes used for stereoscopic vision and the other six for a panoramic view around the spider.

Image: Dan Lieberman / Hidden Wonders /

“Jumping spiders are said to have the best vision of all invertebrates. They catch their prey by ambush, and the large eyes placed close together in the front of the head give accurate stereoscopic vision for judging distance when pouncing. The remainder of its eight eyes give it almost all-round vision, so it can spot prey moving anywhere near it.” (Foy and Oxford Scientific Films 1982:73)

Foy S, Oxford Scientific Films. The Grand Design: Form and Colour in Animals. Lingfield, Surrey, U.K.: BLA Publishing Limited for J. M. Dent & Sons Ltd, London; 1982. 238 p.

Last Updated August 18, 2016

References

Book

The grand design: Form and colour in animals

26/02/1983 | Sally Foy

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