Instructions
Look at the length of the tail. If the tail is longer than the length of the body (including the head) it is likely a black rat. (In brown rats, the tail is a bit shorter than the entire length of the body.) This is the best way to identify a black rat.
Look at its underside. Black rats have undersides that are lighter in color than their backs.
Look at the ears. A black rat does not have hair on its ears. (Warning: Never grab a wild rat so that you can examine its ears!)
Look at the overall shape and size of the body. Black rats tend to be more long and slender than other types of rats. They also have a muzzle that it long and thin in comparison to other types of rats. Black rats grow to be 14 to 18 inches long, including the tail. If the rat is a lot smaller than this, it's not a black rat (unless, perchance, it is a juvenile).
Think about the climate in which this rat lives. Is it warm or tropical? Black rats like to be warm and have migrated to areas of the world that are tropical or subtropical. (In contrast, brown rats do very well in colder climates.)
Watch its behavior. When it flees, does it run upward, perhaps into a tree? Black rats are more likely to be found in trees or in high places than other species of rats. In fact, black rats are known to build nests in trees in some parts of the world.
How to Identify Black Rats
The black rat, "Rattus rattus," is also known by these names: blue rat, roof rat, and ship rat. Identifying a black rat is not as easy as the name makes it sound: black rats are often brown in color, sometimes even tawny. Here are some guidelines for identifying black rats.