A science teacher explains: The world through the eyes of an insect

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The pesky, bloodthirsty houseflies mosquitoes, sugar thieving ants, revolting cockroaches, pretty ladybugs and butterflies, we live in a world of insects. These incredible tiny creatures are fundamental to the balance of nature and play a decisive role in the web of life.

Insects are arthropods, have a segmented body and three pairs of wings, and wear their skeleton on the outside like armor. Most insects have significant visual abilities, but insect optics are incredibly different from ours, so they perceive the world very differently than we do.

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While the human eye is like a megapixel camera and our world is technicolor with a field of view of around 210 degrees, many insects have a 300-360 degree panoramic view of their surroundings, albeit pixelated. They can also perceive ultraviolet light while being blind to red and yellow undertones.

Many insects have a 300-360 degree panoramic view of their surroundings, albeit pixelated. (Photo: Freepik/wirestock)

The eyesight of insects varies greatly between species in terms of depth perception, color recognition and clarity of vision, as they live in different environments and have different visual requirements for food or the escape of predators. Most insects have compound eyes and simple eyes called ocelli.

Compound eyes in insects are located symmetrically on each side of the head. They encompass hundreds, if not thousands, of hexagonal visual units called ommatidia. Each of these units is like an eye in itself, comprising a lens that focuses light and photoreceptors to identify the color. Each ommatidia is surrounded by granules of light-absorbing pigment which counteract light received from neighboring ommatidia. This does not mean that insects see a kaleidoscope of multiple images. The ommatidia are connected to nerve fibers that provide the brain with an image element. The brain forms an image from these independent image elements. Thus, the eye sees only one image, but different ommatidia deliver different parts of it.

The number of ommatidia varies greatly from species to species. The higher the number of ommatidia, the better the resolution and clarity of vision. The dragonfly has more than 30,000 ommatidia, and therefore has excellent vision and visual acuity, allowing them to seize prey even in mid-flight. On the other hand, tiny ants see a blurry world because they can have as few as 150 ommatidia. Thus, the smaller the insect, the smaller the distance at which it can see. But all insects, with quick, ballistic movements of the eye and changing their point of fixation, manage to find potential mates, catch prey, navigate and escape predators. These compound eyes are called apposition eyes and are found in diurnal insects like bees, grasshoppers, and butterflies.

Night insects like moths, fireflies, cockroaches, and beetles have overlapping compound eyes. In the ommatidia of these insects, the lenses and photoreceptors are separated by a pigment-free region called the clear zone. This arrangement ensures that the light refracted by many lenses is focused onto a single photoreceptor which ensures the formation of a high resolution image even in the dead of night when we humans would be essentially blind.

Many species of insects like bees and hoverflies also have simple eyes called ocelli. The large, bulging eyes that are visible on the side of their head are compound eyes. Looking closely, one notices three tiny triangular bumps above the insect’s head. here are the ocelli.

Unlike compound eyes, each ocellus comprises a single lens. The lens can have a very different shape depending on the insect, in bees it is curved and in cockroaches It is flat. Light enters the lens, undergoes refraction and falls on the photoreceptors. However, the image formed is hopelessly blurry. While some eyespots capture light from the sky, others capture light from the horizon. Ocelli are therefore believed to primarily aid insects in navigation and not in pictorial vision.

Flying insects can have two or three and some have no simple eyes at all, while some parasitic insects like fleas have no compound eyes and have only ocelli.

The world through the eyes of an insect will surely be unique and perhaps more colorful. The next time bugs buzz around you and try to squash and kill them, step back and respect them for what they do, from pollinating to cleaning up the environment.

These tiny creatures offer a mega opportunity to unravel the complex phenomena of vision which humanity can benefit immensely through applications in many scientific initiatives such as the development of efficient navigation technology in minimal light and robotic vision. in addition to helping us understand our world more closely.

(The author is PGT-Physics at Shiv Nadar School, Noida.)

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