By Rachna Arora Pesky house-flies, blood-thirsty mosquitoes, sugar pilfering ants, revolting cockroaches, and pretty ladybirds and butterflies, we live in a world of insects. These incredible, tiny creatures are fundamental for nature’s balance 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 a suit of armour. Most insects have significant visual capacities but the optics for insects is incredibly different from our own so they perceive the world very differently from us. Buy Now | Our best subscription plan now has a special price While the human eye is like a megapixel camera, and our world is technicolour with about a 210-degree field of view, many insects have a 300-360 degrees’ panoramic vision of their environment, although pixelated. They can also perceive ultraviolet light while being blind to red and yellow shades. The eyesight of insects varies enormously from species to species in terms of depth perception, colour recognition, and clarity of vision as they live in different environments and have different visual requirements pertaining to food or escaping predators. Most insects have compound eyes and simple eyes called ocelli. The compound eyes in insects are located symmetrically on either 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 the light and photoreceptors to identify the colour. Each ommatidium is surrounded by light-absorbing pigment granules that thwart light received from neighbouring ommatidia. This does not mean that insects see a kaleidoscope of multiple images. The ommatidia are connected to nerve fibres which provide the brain with one picture element. The brain forms one image from these independent picture elements. So, the eye sees one image only, but different ommatidia deliver different portions of it. The number of ommatidia varies widely across species. The more the number of ommatidia, the better the resolution and vision clarity. The dragonfly has more than 30,000 ommatidia, and thus has an excellent vision and visual acuity, enabling them to seize prey even mid-flight. On the other hand, tiny ants see a fuzzy world as they may have as little as 150 ommatidia. So, the smaller the insect, the lesser the distance to which they can see. But all insects, with rapid and ballistic movements of the eye and by changing their point of fixation, manage to find potential mates, catch prey, navigate and escape predators. Such compound eyes are termed as apposition eyes and are found in diurnal insects like bees, grasshoppers, and butterflies. Nocturnal insects like moths, fireflies, cockroaches, and beetles have superposition compound eyes. In the ommatidia of such insects, lenses and photoreceptors are separated by a pigment-free region called a clear zone. This arrangement ensures that light refracted from 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 insect species like honeybees and hoverflies also have simple eyes called ocelli. The big and bulging eyes that are visible on the side of their head are the compound eyes. By close observation, we notice three tiny bumps in a triangle above the insect’s head. These are the ocelli. Unlike compound eyes, each ocellus comprises one single lens. The lens may be shaped very differently depending on the insect, in bees it is curved and in cockroaches it is flat. Light enters the lens, undergoes refraction, and is incident on photoreceptors. However, the image formed is hopelessly out of focus. While some ocelli capture the light from the sky, the others capture light from the horizon. So it is believed that ocelli primarily help the insects in navigation and not in pictorial vision. The flying insects may have two or three and some do not have simple eyes at all, while some parasitic insects such as fleas do not have compound eyes and have ocelli only. The world through the eyes of an insect will surely look unique and maybe more colourful. Next time insects buzz near you and tempt you to swat and kill it, take a step back and respect them for the things they do, right from pollination to cleaning the environment. These tiny creatures offer a mega opportunity to unravel the complex phenomena of vision from which mankind can benefit immensely through applications in many scientific initiatives like developing efficient navigation technology in minimal light and robotic vision besides helping us understand our world more closely. (The author is PGT- Physics at Shiv Nadar School, Noida.) For all the latest Parenting News, download Indian Express App.
