Are Bats Blind? The Truth About How Well Bats Can See

Do bats have eyes?

All bats have eyes, and all of them can see. The size of those eyes varies enormously. Flying foxes have big, dark, forward-facing eyes that give them their dog-like or fox-like look. Many small insect-eating bats, by contrast, have tiny eyes that can be half-hidden in fur, which is one reason people thought they were blind.

Even in the smallest bats, the eyes are not useless leftovers. They have a working retina with light-sensitive cells and send signals to the brain like the eyes of other mammals.

How well do fruit bats see?

Old World fruit bats, also called megabats, depend heavily on their eyes because nearly all of them cannot echolocate. The large flying fox of Southeast Asia has the largest eyes measured among fruit bats in one comparative study, about 12 mm (0.5 in) across.

Fruit bat retinas are packed with rod cells, the cells used for seeing in dim light. In flying foxes and their relatives, densities of about 350,000–800,000 rods per square millimeter have been measured, similar to or higher than in house mice, cats and rabbits. As a result, fruit bats see better than people when light is low, though their vision in bright daylight is less sharp than ours.

Flying foxes also have two types of cone cells, the cells used for color vision. This makes them dichromatic, like dogs: they can tell some colors apart, though not as many as humans. Together with a keen sense of smell, good eyesight lets them find ripe fruit and open flowers in the dark. See What do fruit bats eat? for how they use these senses to feed.

How well do small bats see?

Most of the world’s bats are small insect-eaters that hunt by echolocation. They send out high-pitched calls, usually too high for people to hear, and listen to the echoes to locate insects and obstacles. You can read how this works in How do bats use echolocation?.

These bats still use their eyes. Echolocation works only over short distances, usually a few meters to a few tens of meters, so vision helps with the bigger picture: recognizing landmarks, seeing the horizon, judging when it is getting dark enough to leave the roost and navigating on long flights.

The little brown bat of North America, which weighs only 5.5–12.5 g (0.19–0.44 oz), is a good example. Genetic studies show it has working genes for two kinds of cone cells, one probably sensitive to ultraviolet light. Being able to see ultraviolet may help it spot flowers or insects, since many moth wings reflect UV light.

Where did “blind as a bat” come from?

The expression “blind as a bat” has been used in English for centuries. It probably arose because bats fly at dusk in darting, zigzag paths that look like blind fumbling, and because many small bats have tiny eyes. Bats disturbed in daylight can also look dazzled and clumsy.

In reality, the zigzag flight is what a bat does when it is chasing insects it has detected by echolocation. Far from being lost, it is making split-second turns that very few animals could match.

How did scientists discover that bats “see” with sound?

In the 1790s the Italian scientist Lazzaro Spallanzani found that bats could still fly around obstacles in the dark, and even when they could not see, but became confused when their ears were blocked. He concluded that bats must use their ears in some way to find their path, though he could not explain how.

The answer came in the 1930s, when the American biologist Donald Griffin, working with Robert Galambos, used new equipment to detect bats’ ultrasonic calls. Griffin later coined the word “echolocation”. His work showed that small bats use sound to supplement their vision, not to replace a sense they lack.

Which bats have the best and worst eyesight?

Bats with the best eyesight are generally the big fruit bats. Among echolocating bats, species that hunt by gleaning, picking insects off leaves or the ground, tend to have larger eyes and make more use of sight than fast aerial hunters. Even the bats with the smallest eyes can still detect light and darkness.

So, are any bats blind?

No bat species is blind. Like any animal, an individual bat can lose its sight through injury or disease, but bats as a group see perfectly well for their nighttime lifestyle. The saying “blind as a bat” is a myth, and a better comparison would be “sharp-eyed as a flying fox”.