What Animals Sleep the Most? Ranked by Daily Sleep Hours

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Sleep is universal. Every animal we know of sleeps in some form, from jellyfish to elephants. But the amount varies wildly, and the reasons why tell us something genuinely interesting about what sleep is actually for.

The question of what animals sleep the most comes up more often than you'd expect in conversations about human sleep. People hear that a koala sleeps 22 hours a day and feel a certain kinship. Understanding why those animals sleep so much, and why we don't, helps put our own sleep needs in perspective.

The Sleepiest Animals Ranked by Daily Sleep Hours

The numbers below represent averages across research studies. Individual variation exists within species, and captive animals often sleep differently from wild ones. That said, the patterns are consistent and well-documented.

A Closer Look at the Top Sleepers

Koala: 18 to 22 Hours Per Day

The koala earns its reputation as nature's most dedicated sleeper. The reason isn't laziness; it's their diet. Eucalyptus leaves are extremely low in calories and contain toxins that the koala's liver must work hard to neutralise. Staying still and sleeping is the most efficient way to manage an energy budget that barely breaks even. Their digestive system works while they're at rest, making sleep essentially part of their metabolic process.

Koalas also have a very slow metabolic rate compared to other mammals of similar size, which is itself an adaptation to their restricted diet. They are a clear example of how what you eat shapes how much you sleep.

Little Brown Bat: 19 to 20 Hours Per Day

Bats have extremely high metabolic rates when active, which makes rest essential. The little brown bat is nocturnal, spending nights hunting insects with remarkable echolocation precision. By day, they roost in safe, dark locations (tree hollows, attics, caves) and sleep deeply. Their torpor-like daytime sleep is similar to light hibernation in some conditions, and their REM sleep cycles are well-documented.

Bats also show one of the clearest connections between sleep and immune function. Studies have found that bats host numerous viruses without apparent illness, and researchers have suggested their extended sleep periods may play a role in managing their immune system's interaction with those pathogens.

Giant Armadillo: Around 18 Hours

The giant armadillo is nocturnal and spends its days in burrows where it is largely safe from predators. That safety allows extended, uninterrupted sleep. Its foraging is intensive when it does occur (breaking open termite mounds requires significant energy), and sleep is how it recovers. Giant armadillos are also among the heaviest sleepers in terms of deep slow-wave sleep proportion.

Domestic Cat: 12 to 16 Hours

Your cat sleeps as much as a lion because it is, behaviourally, a small hunter. Cats are crepuscular predators (most active at dawn and dusk) who conserve energy between bouts of high-intensity activity. Even domesticated cats that have never hunted anything retain this pattern. Their sleep is polyphasic (many short naps) rather than one consolidated block, which is also why they can fall asleep anywhere in about 30 seconds.

Why Some Animals Sleep So Much More Than Others

Four main factors determine how much an animal sleeps. Understanding them tells us a lot about sleep's core functions.

1. Metabolic Rate

Animals with high metabolic rates (small mammals, bats, mice) generally sleep more than large, slow-metabolising animals like elephants. High metabolic rates generate more cellular waste, more oxidative stress, and more need for the restorative processes that happen during sleep. Sleep clears the metabolic byproducts that accumulate during wakefulness.

2. Diet Quality and Caloric Density

The koala is the clearest example: a low-calorie diet with high processing demands means staying still and sleeping is energy-efficient. Carnivores like lions also sleep extensively between hunts because a successful hunt provides a large caloric surplus, and the most efficient use of that surplus is rest and digestion, not activity.

3. Predator Risk and Sleep Safety

Prey animals in exposed environments tend to sleep less. Grazing animals like horses and cows sleep 3 to 4 hours. African elephants in the wild sleep only 2 hours per night, the least of any mammal recorded. They can't afford the vulnerability of sleep for long. Bats, armadillos, and koalas all sleep extensively because they have safe, hidden, or elevated rest sites that reduce predation risk during sleep.

4. Cognitive Complexity and Brain Development

Newborns of cognitively complex species sleep more. Human infants sleep 14 to 17 hours per day, and much of that is REM sleep associated with brain development. The same pattern appears in other species with complex nervous systems. Sleep is when synaptic pruning, memory consolidation, and neural development happen. The more complex the brain, the more maintenance it needs during rest.

Animals That Barely Sleep at All

On the other end of the spectrum, some animals have evolved to sleep remarkably little.

African Elephant: 2 Hours Per Night

A 2017 study tracking wild African elephants using activity monitors and GPS found that they slept only 2 hours per night on average, and sometimes went several days without sleep during migration or when sensing predators. They often sleep standing up for short periods, only lying down (which allows REM sleep) every few days. They are the shortest-sleeping mammal on record in the wild.

Giraffe: 0.5 to 2 Hours

Giraffes are extremely vulnerable when lying down and must fold their long legs in a time-consuming process. They sleep in very short bursts (sometimes just minutes) and rarely lie flat. REM sleep, when it occurs, happens in these brief lying sessions.

Bullfrogs: Possibly No Sleep

Research on bullfrogs suggested they may not experience sleep the way mammals do, remaining reactive to stimuli at all times and never showing the characteristic brain activity patterns of sleep. However, more recent studies have questioned this finding, and the question of whether fish and amphibians sleep in the same neurological sense as mammals remains open.

Migratory Birds: Sleep While Flying

Some migratory birds have been shown to engage in unihemispheric sleep (one hemisphere of the brain at a time) while flying. Frigate birds can sleep in flight for seconds to minutes at a time during long ocean crossings. It's not efficient sleep, but it's enough to sustain them across journeys that would otherwise be impossible without rest.

Unusual Sleep Facts from the Animal Kingdom

Sleep research across species has turned up some genuinely surprising findings over the past two decades.

Otters Hold Hands While They Sleep

Sea otters sleep floating on their backs and will hold hands (paw-to-paw) with their partners or pups to avoid drifting apart in currents. Some wrap themselves in kelp for the same anchoring effect. It's functional, not sentimental, but it's one of those animal behaviours that's hard not to find charming.

Sperm Whales Sleep Vertically

Sperm whales have been observed sleeping in vertical pods just below the water's surface, floating motionless like eerie grey logs. They can be approached closely without waking during these periods. This behaviour was only documented in the wild in 2008, and researchers believe it represents a form of slow-wave sleep.

Snails Can Sleep for 3 Years

Under very dry or cold conditions, snails enter a state of extended dormancy (technically closer to hibernation or estivation than sleep) and have been recorded inactive for up to three years. When moisture returns, they wake up and resume normal activity.

Ducks on the Edge Sleep with One Eye Open

Ducks in groups position themselves so that the birds at the edge of the group sleep with one eye open (unihemispheric sleep), while those in the middle sleep fully. The "edge duty" rotates through the group. It's a collective predator-monitoring system built into their sleep architecture.

Sharks May Not Sleep Like We Think

Some sharks must keep moving to breathe (obligate ram ventilators), which complicates traditional sleep. Researchers have observed periods of reduced activity and responsiveness that may constitute a sleep-like state, but the question of how or whether these sharks sleep is still not fully resolved.

What Animal Sleep Teaches Us About Our Own

The diversity of sleep across the animal kingdom points to some consistent principles that apply directly to human sleep.

Sleep Is Restoration, Not Inactivity

Every animal that sleeps is doing something during that time: consolidating memories, clearing metabolic waste (the glymphatic system in humans, which flushes brain waste during sleep, appears to have parallels in other mammals), regulating immune function, repairing tissue. Sleep is not wasted time. It's maintenance.

This is why sleep deprivation has such wide-ranging consequences. It's not just that you feel tired. You're skipping essential maintenance. For more on what happens when that maintenance is skipped, see our article on what happens if you don't sleep for 3 days.

Safety Enables Sleep

Animals that feel safe sleep more and sleep more deeply. This translates directly to humans. Anxiety, noise, an uncomfortable environment, or an unpredictable sleep surface all trigger the same low-level vigilance that keeps a prey animal sleeping lightly. Removing those threats is how you access the deeper, more restorative sleep stages.

Sleep Pressure and Circadian Rhythm Are Universal

Every animal that sleeps operates on two systems: homeostatic sleep pressure (the longer you're awake, the stronger the drive to sleep) and a circadian clock that determines when sleep is most efficient. Disrupting either system, whether you're a human or a bat, degrades sleep quality. Staying consistent with your sleep schedule works with these systems rather than against them.

The Right Environment Makes Deep Sleep Possible

Armadillos sleep 18 hours because their burrows are safe, dark, and at a stable temperature. Cats nap 15 hours because they're comfortable wherever they land. The right surface matters for humans too. A mattress that creates pressure points, traps heat, or transfers motion keeps your nervous system partially alert in exactly the same way an exposed sleeping spot would for a prey animal.

If you're looking to improve your own sleep, the principles your cat and armadillo live by are a good start. See our guide on ways to sleep faster for the practical application.

You might also find our piece on what in turkey makes you sleepy interesting for the chemistry side of sleepiness, or our look at what THCV is for a newer angle on sleep-related compounds.

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• What Happens If You Don't Sleep for 3 Days
• What in Turkey Makes You Sleepy
• What Is THCV and How Does It Affect Sleep