Bats are the only mammals that can fly. Scientists suppose that these unusual creatures appeared more than 60 million years ago. And sometimes they behave very strangely. For example, sleep upside down. Why do they do that?

Hanging upside down can become uncomfortable for people as blood rushes to the head. But for bats it is the most relaxed position. In the same way that some people prefer to sleep on their side or back, bats are most comfortable hanging upside down, holding on with their claws. Since bats are compact in size, the heart can easily circulate blood even when it is upside down. Their claws are unique in that they do not use any energy to hold on to an object.

In addition, bats hanging upside down are in a suitable position to take off quickly in case of danger or in the presence of a food source. Unlike birds, bats do not rise up in flight, so most of them cannot take off from the ground, but must first fall in flight due to their anatomy. Their wings do not generate enough lift, so it is easier for them to fly from a high point.

Bats are nocturnal. They are active at sunset and leave their homes for hunting. During daytime, bats typically hang upside down: sleeping or socializing with other bats.

Bats can remain upside down for long periods of time, including periods of hibernation and even after death. Some bat species can hibernate for five to six months and survive on a small amount of stored fat.