Compound eye

Some bugs have many tiny eyes.

Each tiny eye has its own lens. These lenses catch light from different ways. This helps the bug see a wide view.

These eyes help them see fast things move. This can help them catch food. They see movement very quickly. A honey bee can react faster than a person!

Many bugs use these special eyes to stay safe and find food.

Some animals have a special way of seeing. They use compound eyes. These eyes belong to arthropods. This group includes insects and crustaceans like shrimp.

A compound eye is made of many tiny parts. We call these parts ommatidia. Each part has its own lens. These tiny units help the animal see color and brightness. They also see a very wide view.

Compound eyes are great at seeing fast movement. This happens through something called flicker frequency. This is the rate that the tiny parts turn on and off. Because of this, bugs react very fast. A honey bee reacts in 0.01 seconds. A human takes 0.05 seconds to react.

There are different kinds of compound eyes. Some are called apposition eyes. These make many upside-down images. Others are called superposition eyes. These make one right-side-up image.

Some insects have special zones in their eyes. These zones are called a fovea. In these areas, the eye is flat. This helps the insect see things more clearly. This is helpful for good fliers like dragonflies.

Many arthropods use a special visual organ called a compound eye. This type of eye belongs to insects and crustaceans like shrimp.

Instead of one single lens, these eyes use thousands of tiny units. We call these units ommatidia. Each ommatidium has its own cornea, lens, and light-sensing cells. These cells help the animal see color and brightness. These eyes do not see sharp images like ours do. However, they offer a very large view angle. This helps animals see much of the world at once.

How these eyes work is quite fascinating. Light enters each individual ommatidium through its own lens. The light sensors behind the lens turn on and off. This happens when light intensity changes during movement. This process creates a flicker-effect called flicker frequency. This is the rate that the units turn on and off. It helps animals react to movement very quickly. For example, a honey bee reacts in only 0.01 seconds. A human takes about 0.05 seconds to react.

Scientists group these eyes into different types. Some are called apposition eyes. These eyes form many upside-down images. The mantis shrimp has a very advanced apposition eye. Others are called superposition eyes. These eyes form one right-side-up image. There are three kinds of superposition eyes. Refracting eyes are used by many nocturnal insects. Parabolic eyes are seen in animals like mayflies. Long-bodied crustaceans like lobsters have reflecting superposition eyes.

Some animals have even more specialized vision. Good fliers like dragonflies have a fovea area. This is a special zone of ommatidia. In this zone, the eye is flattened. The facets are also larger there. This allows more light to hit the sensors. It helps the insect see with higher resolution.

A shrimp called Dioptromysis paucispinosa is also unique. It has a large facet that is three times bigger than the others. This creates a mixture of a simple eye and a compound eye.

Compound eyes have also left a mark on human culture. Long ago, people made glass beads called "dragonfly eyes." These were made in Asia between 2000 and 2500 years ago.

Today, the idea of these eyes appears in art and books. There is a novel called "The Man with the Compound Eyes" from 2011. There is also a movie called "Dragonfly Eyes" from 2017. These stories use the idea of seeing the world in many parts. It is a wonderful way to think about how life sees.

A compound eye is a specialized visual organ found in arthropods. This group includes many insects and crustaceans, such as shrimp.

Unlike the single-aperture eyes of humans, a compound eye is made of many small parts. These parts are called ommatidia. Each ommatidium is an independent photoreception unit. Every unit contains a cornea, a lens, and photoreceptor cells. These cells allow the animal to distinguish between different colors and levels of brightness. While compound eyes have poor image resolution, they offer a very large view angle. They are also excellent at detecting fast movement and, in some cases, the polarization of light.

To understand how these eyes work, we must look at the individual ommatidia. Because the eye is a collection of these units, light enters each ommatidium through its own separate lens. This is different from a simple eye that uses one entrance point. As an object moves, the light intensity changes. This causes the individual light receptors behind each lens to turn on and off. This rapid turning on and off creates a flicker-effect. Scientists call the rate of this effect the flicker frequency. This mechanism allows for extremely fast reactions to movement. For instance, a honey bee can respond in 0.01 seconds. In comparison, a human takes about 0.05 seconds to react.

Biologists classify compound eyes into two main types: apposition eyes and superposition eyes. Apposition eyes form multiple inverted, or upside-down, images. In a typical apposition eye, the lens focuses light from one direction onto the rhabdom. The rhabdom is the light-sensitive part of the unit. Light from other directions is absorbed by the dark walls of the ommatidium. The mantis shrimp has a very advanced version of this eye. There is also a group called the schizochroal compound eye. This is a form of apposition eye found in Strepsiptera. In this type, each lens forms an image, and the brain combines them.

Superposition eyes work differently by forming a single erect, or right-side-up, image. There are three specific subtypes of superposition eyes. The refracting superposition eye has a gap between the lens and the rhabdom. It also lacks side walls. Each lens takes in light at an angle and reflects it to the other side. This type is mostly used by nocturnal insects that need to see in the dark. The parabolic superposition eye is found in arthropods like mayflies. In these eyes, parabolic surfaces inside each facet focus light from a reflector to a sensor array. Finally, reflecting superposition eyes are found only in long-bodied decapod crustaceans. This group includes shrimp, prawns, crayfish, and lobsters. These eyes use corner mirrors instead of lenses to manage light.

Some insects have developed highly specialized zones within their eyes to improve vision. Good fliers, such as flies or honey bees, often have a fovea area. This is a specialized zone of ommatidia that provides acute vision. In this fovea, the eye is flattened and the facets are larger. The flattening allows more ommatidia to receive light from a single spot. This increases the resolution of the image.

Another unique example is the shrimp Dioptromysis paucispinosa. It has a refracting superposition eye, but it also features one massive facet in the rear. This facet is three times the diameter of the other facets. Behind it, an enlarged crystalline cone projects an upright image onto a specialized retina. This creates a mixture of a simple eye and a compound eye.

There are also unusual variations of eye structures in the animal kingdom. Some insects possess a single lens compound eye. This is considered a transitional type between a multi-lens superposition eye and a simple eye. Another version is the pseudofaceted eye found in Scutigera. This eye consists of a cluster of many ocelli, which are simple eyes, organized to look like a compound eye. Interestingly, asymmetries in compound eyes can relate to behavior. For example, the ant Temnothorax albipennis shows a bias toward making left turns. This behavior is correlated with slight asymmetries in their compound eyes, specifically a difference in the ommatidia count.

The concept of the compound eye has even appeared in human history and culture. Between 2000 and 2500 years ago, people in Western and Eastern Asia made glass beads called "dragonfly eyes." These knobbly, multi-colored beads are a famous cultural reference. In modern times, the compound eye continues to inspire art and literature. You can find references to these eyes in the 2011 novel "The Man with the Compound Eyes" by Wu Ming-yi. There is also the 2017 movie "Dragonfly Eyes" by Xu Bing. These works often explore the unique way these creatures perceive the world around them.