It’s a misconception that dogs don’t see colors, they just don’t perceive as many as we do. But they can see better in the dark and register tiny movements.
Much research has been done on canine vision. You may be familiar with the myth that dogs only see black and white. That’s not right: dogs can distinguish about 40,000 shades. In humans, that’s over a million.
Dog eyes have the same type of color-sensitive cells (cones) as human eyes. Only we have three types of cones and dogs only two. A dog’s cones are sensitive to blue and yellow light. As a result, they can distinguish blue and yellow, but not red and green.
It is therefore suspected that dogs experience the world in the same way as humans who are red-green color blind, perceiving a range of shades of gray instead of those two colors.
In addition, dogs can see less close up than humans and they are less sensitive to changes in light intensity. On the other hand, their pupils can dilate further than ours and they have a reflective layer in the retina (tapetum lucidum), which makes them see better in the dark.
Dogs also have more light-sensitive rods than we do. They only perceive shades of gray, but are very sensitive to light and good at detecting small movements at a great distance.
Garden snails see particularly poorly, but just enough to seek protection in their home in time if danger looms.
The small, common garden snail has eyes on the end of its tentacles. The eyes are hard to spot, but they look like black dots.
Snails see very little, because although their eyes contain a fluid-filled cavity with a lens in front of them, they have no muscles to control this lens. This prevents the snail from focusing. Researchers therefore think that snails see shapes and shadows rather than actual images.
A snail can detect a fellow species crawling by, movements in the environment or suddenly appearing shadows. That is enough to quickly flee into his house.
The eyes of a garden snail also do not contain color-sensitive cells. He therefore only sees shades of gray and can only distinguish between light and dark. Because it detects differences in light intensity, the snail can look for dark places to stay for a long time, for example in winter.
Despite its poor eyesight, the garden snail still performs well compared to other molluscs, such as giant clams and squid.
Praying mantis shrimp sees direction of light
The most advanced eyes in the animal kingdom are those of the mantis shrimp. To understand the many visual inputs, the animal has recoded its brain.
The mantis shrimp has the most advanced vision of any animal known. Its eyes move independently of each other and contain sensory cells for 12 colors – four times as many as human eyes.
In addition, the mantis shrimp can see the polarization of light. Light and other electromagnetic waves always fall perpendicular to the direction of propagation, and the polarization reveals which way they reflect – and thus whether a potential prey or enemy is moving towards or away from the mantis shrimp. Polarization therefore gives the animal extra detailed visual information when hunting or fleeing.
Polarized sunglasses and camera lenses have a similar effect. The light that hits our eyes goes in all directions. With the filter, directions of, for example, reflected sunlight on a water surface are sorted out, so that you can see into the water.
For a long time it was the question of how the mantis shrimp can use its little brain to make chocolate out of its own hyper-complex visual impressions.
In 2019, a team of Australian, American and Swedish researchers got a little closer to the answer. They discovered that the processing of the visual data already starts in clumps of neurons in the stalks on which the eyes sit.
It was also found that the animal has recoded neurons involved in the sense of smell in other crustaceans for vision.
The 200-kilogram giant clam sees the world as luminous dots through its many micro-eyes.
The giant clam is the largest mollusk in the world. Some live more than 100 years and are 1.2 meters in diameter and weigh 200 kilos. Its eyes are among the simplest of evolution: ocelli or pointed eyes.
Each ocellus has a small cavity with an opening that acts as a pupil. The back of the cavity has hundreds of light sensitive cells. The animal can see three colors, but cannot combine them into shades.
The simple eyes can only be effective if the giant clam has a lot of them. Therefore, the edge of the animal’s mantle is covered with hundreds of eyespots, each about 0.5 millimeters.
The simple ocelli allow the font shell to respond to light and shadow. Research even shows that, despite its simple eyes, the giant clam can respond to movement and shapes before, say, a predator casts its shadow directly on the animal.
When Australian researchers first demonstrated the giant clam’s vision in 1986, they were amazed that it could detect variations in light intensity in different parts of the visual field in this way.
With two kinds of eyes, the flying honey producers navigate without hesitation to the flowers with the most nectar.
Bees have compound eyes, which consist of 4500-5500 immobile partial eyes or ommatidia. The compound eyes give bees a color vision that works very differently from ours.
Where we have sensory cells for blue, green and red light, bees have cells for blue, green and ultraviolet light. So bees do not see red and orange, but they see very well blue and green. In addition, they see ultraviolet light – short-wavelength light that is invisible to us.
Many flowers take advantage of the special sight of bees with stripes on their petals, which point the way to the nectar. This allows bees to spot the flowers that are most ripe for pollination.
In addition to the compound eyes, bees have three pointed eyes on top of their heads. They register changes in light intensity and can, for example, observe the shadow of an enemy attacking from above.
Scientists have also discovered neurons in the bees’ brains that process input from a special vision function that helps the animals see which direction light is going – polarization.
The polarized light creates a luminous band across the sky along which the bees navigate. The band is also visible to the bees when the sun is hidden behind a cloud cover.
