Why do bats sleep upside down?

Answer

Dear Sarah,

The front legs of bats are completely transformed into wings. They still have claws on those wings, and they can hang onto something with those claws for a while so that they do NOT hang upside down but just upright. But that’s way too tiring to endure to sleep. It is also much more difficult to fly back from that attitude. And if you hang upright on a wall or ceiling, you can’t really see what’s happening around and below you! It is therefore easier for bats to hang on their hind legs. Those hind legs are also completely transformed and are fused with the back of the wings. But they also have claws on them that they can hang on to. When they hang on their hind legs, they hang upside down. They cannot, like a bird or something, or like a squirrel, stand on a branch because their legs are completely fused with their wings. So they have to hang. That is also very safe by the way, if they hang somewhere high on a branch or on a wall or ceiling with their hind legs it is difficult to catch them, they can see well what is happening around them, and they can also easily fly back. But every now and then a bat will just land on its belly on a flat piece. You can see that in the following picture if you click on it: