THE EYES HAVE IT

TWO FRONT-FACING EYES WORKS WELL FOR US BUT NOT FOR EVERYTHING ELSE. THESE ANIMALS HAVE SOME BIZARRE AND BEAUTIFUL EYES THAT LET THEM SEE THE WORLD IN VERY DIFFERENT WAYS

- DR HELEN PILCHER

HAIRY HUNTER

ORNATE WANDERING SPIDER, BRAZIL

It seems that spiders don't like odd numbers. Two body segments, eight legs, one to four pairs of spinnerets and always an even number of eyes. Most spiders, like this ornate wandering spider, have eight simple eyes, but some have six or two. The way a spider catches its food has a strong influence on the ways these eyes are arranged. Web-building spiders, for example, tend to have smaller eyes that are evenly spaced apart, but the more centrally placed eyes of visual predators, like our friend here, are often enlarged. All the better to glimpse a tasty morsel with! There are principal eyes (the bottom pair here) and secondary eyes (the rest), which differ in structure and function. Principal eyes have sharp vision, along with retinas that can move behind their fixed lenses, helping the spider to track its prey. Meanwhile, the secondary eyes work together to provide a wider field of view, and identify objects and movements of interest.

SEEING RED

RED-EYED TREE FROG, COSTA RICA