Animals That Don't Sleep

Dolphins Mature dolphins do not sleep in a clearly recognizable way. They literally sleep with one eye open, in a process called unihemispheric sleep. Because they have to regulate their breathing consciously, one half of the dolphin's brain will stay awake at all times while the other half rests.

Great Frigatebirds The great frigatebird (Fregata minor) is another species capable of unihemispheric sleep. Unlike dolphins, great frigatebirds can utilize this strategy simply when needed. Researchers were able to rig up small devices that measured brain activity and found that while performing long-distance, transoceanic flights, these birds only slept in half their brains and only did so for an average of 42 minutes (compared to the over 12 hours they get on land).

Fruit Flies Some insects sleep for extremely short periods. For instance, small percentages of female fruit flies (Drosophila melanogaster) were found to sleep for an average of 72 minutes per day, with one specimen found to sleep for only 4 minutes a day.

Jellyfish Until recent studies demonstrated otherwise, it was thought that animals without a central nervous system, such as jellyfish (like Chrysaora fuscescens), either did not need or were incapable of sleep.

Bullfrogs Bullfrogs (Lithobates catesbeianus) did not sleep since they reacted to stimuli in a similar manner at all times. However, this idea has been dispelled and replaced by the notion that they do snag intermittent moments of rest, though never sinking into a full, inattentive slumber. 

Orcas 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.

Tilapia 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.

Butterflies 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.

Walrus 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.