Rat

Rats are small, adaptable rodents found throughout Middle-earth, from bustling towns and farmlands to deep, dark tunnels and abandoned ruins. They are prolific and opportunistic, thriving wherever food and shelter are available, and are notorious for their persistence and cunning.
Rats are always aggressive and attack in swarms, using their numbers to overwhelm larger foes. Some individuals are resistant to Cries, while others carry diseases that can afflict unwary travelers. Their sharp teeth and quick reflexes make them a constant nuisance in both urban and wild environments.
Despite their size, rats are a serious threat when encountered in groups, and caution should be exercised in areas known to harbor them. Few creatures inspire as much revulsion, yet their resilience and adaptability have allowed them to survive in nearly every corner of Middle-earth.
Check this list for all known sub-species: