We all know there can be dangerous side effects from sleep deprivation in humans and it’s healthy to get your average of 7 or 8 hours a night. In the animal kingdom, sleep habits also range significantly. Some animals sleep hanging upside down or buried under mud, while others sleep standing up or while they are swimming. It’s normal to wonder, are there animals that don’t sleep at all?
We can’t say there is an animal out there that doesn’t need rest or eventually doesn’t go into a sleep-like state, like during brumation. However, you’ll be surprised to learn how long some animals can go without sleep. Or how some don’t need what we traditionally call sleep, such as inactivity and non-active brains. Read on to learn more about 10 animals that can survive without sleep.
10 animals that don’t sleep
From animals that go months without sleep to species that have brains that are always alert, here’s a list of 10 animals you might be surprised can survive without sleep!
Scientific family: Delphinidae
Newborn dolphins don’t sleep for a month after birth and stay alert with at least one eye open at all times. They will also continuously surface for air every 3 to 30 seconds. During this time, scientists found that the mothers will stay awake as well.
In general, all dolphins also engage in what’s called uni-hemispheric sleeping, where half of their brain will stay awake all the time. They then switch which side is awake to make sure their entire brain rests. This technique helps them stay safe while resting and remain alert to predators such as sharks. Another fun fact is dolphins can swim while they are sleeping.
Scientific name: Orcinus orca
Also known as killer whales, orcas are another species where babies spend their first few months without any sleep. Even when the adults are sleeping, you can see young orcas swimming around.
One of the main reasons why baby orcas, or calves, need to move around constantly is to keep their bodies warm. Once they grow large enough to have blubber protecting them, then they can start resting and sleeping.
3. Fruit fly
Scientific name: Drosophila melanogaster
Scientists have found that fruit fly sleep habits vary from fly to fly. While some flies sleep for 10 hours a day, others don’t sleep at all or survive on just 4 minutes of sleep per day. In an experiment, they also found that fruit flies deprived of sleep lived just as long as the flies who slept “normally.”
4. Alpine swift
Scientific name: Tachymarptis melba
Alpine swifts have incredible migration habits where they travel from Switzerland to West Africa. During this flight, they can fly continuously for 200 days straight – that’s 6 months. These birds won’t even land or stop on treetops to rest during this time.
While scientists are unsure if they have some special way of resting or sleeping while flying, the birds are constantly active in the air, even during periods where their wings aren’t flapping as much.
Scientific name: Lithobates catesbeianus
Bullfrogs always stay alert and react to stimuli as if they are awake even when they appear to be resting. However, these frogs do enter a state of brumation each year, which some people consider a form of binge sleeping after no sleep. For all the other months, they seem to “rest” but never reach the inactivity or deep slumber of sleep.
A 1967 study discovered this active resting period and is widely cited as evidence that bullfrogs don’t need sleep. Scientists today are questioning this, though, and want more studies to truly understand the resting periods of bullfrogs and how they survive until brumation.
Scientific name: Pomatomus saltatrix
Bluefish also called snapper or tailor, are a high migratory species that seasonally move along the U.S. Atlantic coast. Most wild fish will stop sleeping during their migration periods. Additionally, even when bluefish appear to be sleeping, they still swim constantly and respond to stimuli.
Scientific name: Oreochromis niloticus
Besides migration, sleep patterns in fish also vary when it comes to caring for their young or right after birth. In the case of tilapia, these fish are known to stay awake and active for the first 22 weeks after birth. While scientists have observed adults going into a sleep-like rest state, these behaviors don’t exist in juveniles.
8. Upside-down jellyfish
Scientific genus: Cassiopea
Suppose the definition of sleep requires your brain to be in a state of inactivity. In that case, animals like the upside-down jellyfish that have no brains technically can’t sleep. Instead of a brain, they have a network of sensors and tentacles that help them feed on tiny sea creatures and zooplankton.
However, a 2017 study did find that these jellyfish enter into what is similar to a sleep-like state. During these periods, they decrease their activity and have slower responsiveness to stimuli. So perhaps even without brains, these animals still need to rest every now and then.
9. Rhopalocera (butterflies)
Scientific suborder: Rhopalocera
Most insects, such as butterflies, don’t actually sleep but go into a state of torpor. Torpor appears like sleep but is when they rest with a lower body temperature and slower heartbeat. They also rest with their eyes open among foliage or hanging upside down from twigs or leaves.
Scientific name: Odobenus rosmarus
You might associate lazy and sleepy with walruses, but these large animals can easily stay awake for 84 hours at a time. They’ll mostly spend these hours swimming and looking for food. After long periods of non-sleep, though, the walrus will make up for it with an extended snooze – and in a fascinating way too!
Walruses can sleep in the water without drowning because of special muscles near their throats that act as air sacs. The air sacs can hold up to 13 gallons of air and keep their heads vertical above water even while they sleep.