Most rodents are small in size. However, the largest rodent, capybara may weigh up to 65 kg. In the wild they are known to live less than two years, whereas, in captivity the life span may be up to five years. Rodents are useful as well as harmful animals. It is useful in the sense that some rodents are highly valued for their fur (e.g. chinchilla and beaver) and biomedical research (e.g. guinea pigs, rats, mice and hamsters). Their harmful effects have also attracted a worldwide attention. Some rodents are responsible for damaging agricultural crops and seeds of grains. They consume lot of grains causing a great loss to the farmers. The drainage systems in the cities and agricultural fields are also damaged by these animals. Rodents are widely known to be the reservoirs of many dreadful diseases (e.g. bubonic plague and tularemia). Some species are also known to kill domestic chickens and occasionally eat their eggs.