Peromyscus eremicus, commonly known as the cactus mouse, is a small rodent that is native to the southwestern United States and northern Mexico. There are several synonyms for this species, including Peromyscus eremicus eremicus, Peromyscus spinatus, and Peromyscus fallax. The cactus mouse is well-adapted to life in arid environments, and is known to use cactus pads for food and water. These mice are nocturnal and mostly solitary, living in rocky deserts and scrublands. The cactus mouse is an important species in its ecosystem, serving as prey for many predators and aiding in seed dispersal for plant species.