Here you will learn about the rodents of the cooler regions. This would include rats, mice, and lemmings. They are all rodents because they gnaw and have a long narrow tail. A rodent is a mammal with front and back teeth. They use the front to gnaw and back to grind. All rodents have two top and two bottom teeth in the front called incisors. The teeth wear away at the tips, but don’t wear out until the animal is old. The rodents also have back teeth called molars to grind and chew the food so it digests easily. Rodents are both helpful and harmful to humans. A rodent might eat up your easy to reach household foods or it might eat harmful insects and weeds.