It is common knowledge that tails aid mammals with balance and coordination, and maybe that’s why I constantly walk into walls-I don’t have a tail. Rat tails, however, are particularly special. 

Rats have six veins and one ventral artery in their tails. They use these for thermoregulation, which regulates their body temperature. Rats can use their tails to disperse about 17 percent of their body temperature. That’s like having a built-in cooling system!

A large reason rats can use their tails this way is because of the tail’s design. They have a large surface area-to-volume ratio, meaning that it has a large surface area with respect to its volume. This allows heat to easily be lost through the surface of the tail. 

When a rat’s body temperature increases, the diameter of their blood vessels does as well. The larger vessels allow more blood to flow into the tail, and while more blood is there, more heat is lost. 

Some rats do not have tails. Two genetic mutations, Tal and St, can cause a rat to grow without a tail. Both of these mutations can be lethal to the rat if inherited in a homozygous state, meaning the new rat will receive two copies of the gene. A rat with 2 copies of the Tal gene will die at about 9 days gestation before it is even born. A rat with two copies of the St gene will most likely live long enough to be born but will die shortly after.

Only rats with one copy of these mutations survive, and they survive without a tail. This makes them take on average an hour longer to cool down compared to normal rats. Rats are not the only animals that use their tails for thermoregulation. Beavers also use their tails to cool down. A number of furry animals use their tails to keep warm too.