From Halopedia, the Halo wiki
Rodents are small furry mammals belonging to the order Rodentia. On Earth, rodents are the largest and most diverse group of all mammalian animals. Well-known rodents include rats, mice, squirrels, porcupines, beavers, gophers, hamsters, and capybaras. Different species of rodents and other rodent-like creatures could be found throughout the galaxy.
Although various species of rodents are considered vermin by many cultures, they were nonetheless a viable source of food when really needed. Rodents at times were hunted and even consumed by both human and Covenant alike. On Eayn, Kig-Yar snack vendors in Tilu City sold loops of small rodents that were strung together like beaded necklaces.
Rats are long tailed rodents commonly regarded by many humans as invasive pests. For centuries, rats on earth have lived and thrived in human cities. By continuing to follow humans across great migratory routes by ships, rats have managed to spread offworld to infest settlements on other Human colonies. They are distinguished from mice in their larger size and some are kept as pets or used for scientific study.
Squirrels are a small mammalian species native to Earth on several continents. Squirrels are herbivorous, eating a basic diet of nuts, small plants and seeds. They also live in trees in order to hide from predators and to raise young.
Similar animals, also referred to as "squirrels", have been noted to live on several planets, including Reach until its destruction by the Covenant. The young Spartan-IIs survived several days on squirrels during one of their war game sessions with Tango Company, where they had to capture a flag.
Zeta Halo rodent
The Forerunners procured a gopher-like species before the firing of the Halo Array and preserved them on Installation 07. These short tailed critters possess three toes on each paw with large claws, which they use to dig and burrow into the ground when startled. They are covered in multicolored fur with distinctive white fur markings. Their most prominent feature is their unique segmented hoods on their nasal bridges.
List of appearances