Do animals sleep like humans? Do snails sleep of their shells? Why doesn't a whale sink when it sleeps? – Lucinda, age 5, Reid, Canberra.
Great questions, Lucinda!
Most animals, including snails, sleep such as you and me. That is, they get into a cushty position and shut their eyes (in the event that they have eyelids!) Like you and me, they don't move much while sleeping. But how will we know if the animal is sleeping, or simply still?
There are a number of things that come together to assist us tell if an animal is sleeping. A sleeping animal is just not aware of all the pieces happening around it. If you disturb a sleeping animal, nonetheless, you may still wake them up quickly. Most animals also need a specific amount of sleep every day. If they don't get enough sleep, they sleep later (and more deeply) to make up for it. This is true for all people as well.
Pond snails use things like rocks or the side of their aquarium as their bedding, curling up while they sleep. Although it doesn't look particularly comfortable, their shells hang away from their bodies, and so they keep their tentacles inside their shells. Scientists don't yet know much about how other snails sleep, but they likely sleep similarly.
While most animals sleep like this, relaxed and motionless, some animals sleep quite otherwise. Cows arise and chew their cud while sleeping. Ostriches sleep with their eyes open and their heads high off the bottom. Some birds can fly while sleeping and dolphins can sleep while swimming. So even when an animal appears awake, it could be sleeping.
Whales don't sink while sleeping because, like dolphins, they will float on the surface of the water while sleeping. People have also seen whales swimming under the surface of the water, which could also be one other way for whales to sleep. They can rest like this for half an hour or more, but they can't drown because they will hold their breath longer than we are able to.
We know that many animals, perhaps all animals, sleep. We know that birds, reptiles, frogs and fish also sleep. Even bugs and jellyfish sleep. Because so many alternative animals sleep, this seems very necessary. We still don't know why animals began sleeping in the primary place.
There are many other things about sleep that we don't know. Scientists haven't yet studied sleep in all animals, so we cannot say of course that animals sleep. Some animals are also difficult to review. For example, sea sponges are animals, nevertheless it could be hard to inform in the event that they are sleeping or awake!
We don't even know if other animals dream, like we do. You could have seen pet cats and dogs moving while they sleep as in the event that they were chasing other animals. This could mean they're dreaming, but again, it's hard to know of course.
CC BY-ND