For such a quiet and peaceful animal, there are surprisingly many urban legends about cows. Some common myths include cows’ sleeping schedule predicting the rain, cows sleeping standing up, and cows being unable to lie on their sides.
We’ve debunked all these myths already here on FaunaFacts, but here’s another interesting one that seems just plausible enough that it might be true: Can cows sleep with their eyes open?
It turns out that cows sleeping with their eyes open is just an urban myth. Cows do not sleep with their eyes open, they close both their eyes when they fall asleep just like humans do. This helps protect their eyes from insects, dirt, and other damage while they sleep.
In this article, we’ll look at this myth in a bit more detail, find out what cow behaviors spawned the myth in the first place, and explore the biology behind cows closing their eyes at night.
Do Cows Sleep With Their Eyes Open?
If you were to bring this question up to a farmer, they would probably laugh at your naivety. Darn city-folks don’t know nuthin’ about cattle!
It’s a common misconception that cows sleep with their eyes open. Cows sleep with both eyes closed, just like humans.
Although it may seem obvious to some, lots of animals DO sleep with their eyes open and it’s one of those things that sounds just barely plausible enough that it might be true. Combined with all the other popular legends about cows’ sleep, (many people know cows can see well in the dark) it’s not hard to see why you might believe it.
Cows spend up to 14 hours per day lying down dozing, but only 30 minutes per day in restful sleep. When cows lie down for long periods to ruminate, it sometimes looks like they are sleeping, and this may explain where the myth comes from.
While cows are dozing, they are still awake. If you get close enough to them you’ll see their mouths slowly grinding from side to side as they regurgitate and chew the partially digested grass from their rumens.
Why Do Cows Close Their Eyes When They Sleep?
Cows close both their eyes at night just like us.
Cows close their eyes when they go to sleep…
- To protect their delicate eyes from any dirt
- To stop their eyes from drying out overnight
- To keep bugs and insects away from them
- To prevent damage to the delicate outer eye layer (cornea)
If cows were to sleep without closing their eyes, they would be leaving their delicate eyeballs vulnerable to damage. Dirt would get into their eyes and cause infection, flies and other insects might bite them or lay their eggs there, and their eyes would dry out in the wind.
Do Any Animals Sleep With Their Eyes Open?
Although cows sleep with their eyes closed, many animals keep one or even both eyes completely open while they sleep.
Keeping one eye open during sleep is sometimes called unihemispheric sleep, because the animal effectively shuts down one hemisphere (half) of their brain to let it rest while the other half keeps the animal on autopilot, looking out for any predators.
This is most common in fish, but is also found in some birds including chickens, and some mammals including bats, seals, and otters.
Animals who sleep with both eyes open include some reptiles and fish, many of which don’t have eyelids so couldn’t close their eyes even if they wanted to.
Table of animals who sleep with one or both eyes open:
|Domestic Cattle (Cows)||Both Eyes Closed|
|Dolphins||One Eye Open|
|Fruitbats||One Eye Open|
|Sharks||Both Eyes Open|
|Koi||Both Eyes Open|
|Elephants||Both Eyes Closed|
|Lizards||Both Eyes Closed|
|Chickens||One Eye Open|
Do Cows Have Eyelids?
Cows have eyelids just like humans that close when they sleep, but they also have a special third eyelid that we don’t have, which offers them an extra layer of defense against dirt and flies.
The third eyelid is called the nictitating membrane. The nictitating membrane is used to clean and moisten the eye, keep it from drying out, and protect it from injury. It’s also used for scratching an itch on the eyeball. Unlike our two upper eyelids that blink continuously, cows use their third eyelid only occasionally.
It’s completely clear and allows them to blink without losing their vision.
In summary, cows don’t sleep with either of their eyes open when they go to sleep. Cows sleep with both eyes very firmly closed. Cows even have a special third eyelid for an extra layer of protection.
Though it’s completely false, cows sleeping with one or both eyes open is a popular urban legend, and probably came about from the fact that cows spend a large part of their days dozing while they digest their food. In this state, cows are very still, but they are still awake.
Although cows’ eyes are firmly shut while they sleep, some animals keep one or even both eyes open while they sleep. Seals, sharks, bats, chickens, snakes, and dolphins all keep at least one eye open while they sleep.