Norway rats are the largest of the introduced species. They can reach lengths of up to 18 inches including the tail. The tail itself ranges in length from six (6) to eight and one half (8 ½) inches and are conspicuously hairless. Brown and black coarse fur covers the majority of the animals with the undersides of the Norway rat are gray to yellow. The overall weight of these animals is only about one (1) pound. The Norway rat has a generally stocky appearance with a blunt nose and shorter ears.

Roof rats are a bit smaller than the Norway rats, save for their ears which are actually long enough to reach their eyes when folded over. Size wise, the Roof rats are much smaller. Weighing in at only one-half (1/2) of a pound. The tail of the Roof rat is longer than that of the Norway rat measuring almost as long as their body. Their coloring is brown with black on top of coarse fur and a belly that is more often than not white in hue. The nose of the Roof rat is pointed.

Young rats are often confused with house mice. To help distinguish between the two (2) take note of the size of the feet. Juvenile rats will present with very large feet in comparison to the rest of their body.

Woodrats are a little smaller than the introduced species of Roof and Norway. They can also be distinguished from them by way of their soft and fine fur, light colored feed and most importantly, their fur covered tails.