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Anyone who has ever observed an insect has immediately noticed a big difference in their bodies compared to the rest of the animals on this planet. The eyes in particular seem to catch the attention of the curious individual. It's no the fact that there is one eye, but that there seems to be many. This is because arthropods (insects) have evolved separately from annelids, cephalopods, and vertebrates. In fact, it almost seems as if the eye developed in a backward fashion than the rest of the eyes seen today. What lead to the formation of the eye of the family of organisms which occupies almost every niche of this planet? What advantages and disadvantages are there to having a compound eye? Finally, what do many believe the vision of insects looks like?



The Theory on how the Insect Eye Formed

Unlike the development of the cup-like eye, which evolved through a continued bending of the photoreceptors concavely (inward), the insect eye is theorized to have formed by bending in a convex direction (outward). Similar to the bacterial eyespot, the image received by the surface of the newly forming eye of the arthropod ancestor would be projected on to an opaque surface which would then be interpreted by the processing center of the organism as an image (Nillson, 299). At first, single lenses would be used, but eventually multiple lenses would prove to be an evolutionary advantage. This evolution brought forth the evolution of the compound eye. The evolutionary advantage of the eye: if more "eyes" are present, a higher resolution can be seen. Also, with more of these eye-like structures, more directions can be seen. This accounts for the 3000-9000 ommatidia3 found today in many insects, and the 25000 found in each eye of fast moving insects such as dragonflies (Patton).

















The Advantages and Disadvantages of the Insect Eye

Insects have many advantages and disadvantages in possessing compound eyes. The biggest advantage to being an insect has to do with their field of view. Insects, such as the dragonfly, have extremely large eyes, which can see in every direction except for the blind spot created by their bodies (Patton). They can also have a dual-vision system, which means that they can see both dark and light, and color (Pichaud). This can be seen in pollinating insects, such as bees, which rarely get a mature flower mixed up with a maturing or dying one. Unfortunately, insects do not have the best resolving power in the animal kingdom. One degree of arc of a human eye resolving at 1 meter can make out many details of a human hand, whereas a similar portion of an insect eye at its best resolution, looking from the same distance, can only make out an outline of the hand (Patton).



3Ommatidia: one of the elements corresponding to a small simple eye that make up the compound eye of an arthropod
(as according to: Merriam-Webster Online)