Just as people without color vision have a hard time understanding what color is, it is impossible for humans to imagine what it is like to see through the compound eye of an insect. These eyes are made of thousands of tiny rods called ommatidia, each one a small eye connected directly to the brain. Scientists theorize that the insect's brain composes the images received from each ommatidium, enabling it to perceive movement in any possible direction-in some species, even from behind. •
One Eye, or Thousands
Each ommatidium is responsible for a small portion of the visual field. Depending on the type of light they receive, the pigmented cells around each rhabdom can vary their diameter, regulating the overall sensitivity of the compound eye.
Field of Vision
A fly's ommatidia are arranged in circles, and each one covers a portion of the field of vision. Such systems may not yield a high-resolution image, but they are highly sensitive to movement. The slightest motion causes a transfer of sensitivity from one ommatidium to another. This is what makes it so hard to catch a fly.
FIELD OF VISION OF A FLY
Sections of field of vision
A Bee's Eye View
Compared with human vision, a bee's vision is somewhat nearsighted. Even the images of nearby objects are blurry. Its compound eyes have some 6,900 ommatidia.
HEADED FOR NECTAR
Sensitivity to ultraviolet light, invisible to the human eye, enables worker bees to find the nectar inside the flowers.
180° field of vision
Human field of vision
With binocular vision, a flat and undistorted image flAB
In a larger field, the same image is narrower.
The mouth has apparatus for licking and sucking.
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PROTECTIVE VISION IN THE ROUND CALCULATORS
The eyelets of the Certain dragonflies have This common blue tachinid fly cover a completely spherical damselfly uses its eyes its eyes. field of vision. to calculate distances.
THE HOUSEFLY HAS
Connects each lens with its nerve
Cone-shaped, to direct light to the rhabdom lE^fl vttkfl
Hexagonal in shape to fit into the rest of the compound eye
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