A rodent is a type of mammal with large, sharp front teeth that never stop growing. These teeth are perfect for gnawing, which is what rodents do constantly: they chew on nuts, seeds, bark, and almost anything else to wear down their teeth and keep them from getting too long. If a rodent stopped gnawing, its teeth would eventually grow so long it couldn't close its mouth.

Rodents are the largest group of mammals on Earth. Mice, rats, squirrels, hamsters, guinea pigs, beavers, porcupines, and chipmunks are all rodents. They live almost everywhere: in forests, deserts, cities, and even in people's homes (usually uninvited). A beaver can gnaw through a thick tree trunk to build a dam, while a tiny mouse can chew through cardboard boxes in your pantry.

Scientists classify animals as rodents based on their special gnawing teeth, called incisors. These teeth have hard enamel only on the front surface, so they sharpen themselves naturally as the rodent chews. This design has helped rodents thrive for millions of years, adapting to nearly every environment on the planet. Despite their small size, rodents play important roles in their ecosystems: spreading seeds, providing food for predators, and helping scientists understand human biology through laboratory research.