The cactus mouse or cactus deermouse (''Peromyscus eremicus'') is a species of
rodent
Rodents (from Latin , 'to gnaw') are mammals of the Order (biology), order Rodentia ( ), which are characterized by a single pair of continuously growing incisors in each of the upper and Mandible, lower jaws. About 40% of all mammal specie ...
in the family
Cricetidae
The Cricetidae are a family of rodents in the large and complex superfamily Muroidea. It includes true hamsters, voles, lemmings, muskrats, and New World rats and mice. At over 870 species, it is either the largest or second-largest family ...
. It is a species of the genus ''
Peromyscus
''Peromyscus'' is a genus of rodents. They are commonly referred to as deer mice or deermice, not to be confused with the chevrotain or "mouse deer". They are New World mice only distantly related to the common house and laboratory mouse, ''M ...
'', a closely related group of
New World mice often called "deermice". They are native to desert areas of western
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
.
Description
Cactus mice are small
cricetid rodents, with large eyes and ears, a pointed snout, and a long monocolor tail. Average dimensions for ''P. eremicus'' are as follows: total length, ; length of body, ; length of tail, ; length of hind foot, ; length of ear, ; greatest length of skull, and zygomatic breadth, . Adults weigh between . Females weigh slightly more than males and are significantly larger in body length, ear length, length of mandible, and bullar width of skull.
Cactus mice can be identified by having naked soles on their hind feet and almost naked flesh-colored tails (as opposed to the furry bicolored tail common in most ''Peromyscus'' species), which are usually the same length or longer than the animals' body length. Their ears are nearly hairless, large, and membranous.
Their fur is long and soft; coloration varies between subspecies and between different populations. Color of fur varies from
ochre
Ochre ( ; , ), iron ochre, or ocher in American English, is a natural clay earth pigment, a mixture of ferric oxide and varying amounts of clay and sand. It ranges in colour from yellow to deep orange or brown. It is also the name of the colou ...
to cinnamon, with white ventral areas, and the sides and top of head slightly grayish.
Females tend to be slightly paler in color than males, while juveniles appear more gray than their parents.
Cactus mouse longevity is around one year in the wild, but in captivity can live up to 7.4 years.
Distribution
Cactus mice are found in dry desert habitats, steppe, and mountain foothills in arid regions of the southwestern United States and northern Mexico, as well as islands off the coast of the
Baja California peninsula and in the
Sea of Cortés. Low average temperatures and lack of the mesquite species ''
Prosopis juliflora'' might limit northern expansion.
The cactus mouse occurs sympatrically with five other deermouse species, including the
California mouse,
canyon mouse,
Eva's desert mouse,
mesquite mouse, and the
western deermouse.
Diet
The cactus mouse feeds on seeds, mesquite beans, hackberry nutlets, insects, and green vegetation. In winter, they rely more on insects; on seeds and flowers in the spring; and seeds, leafy greens, and insects in the summer. In autumn, they transition to their winter diet.
Behavior
Cactus mice, like most
muroids, exhibit
crepuscular
In zoology, a crepuscular animal is one that is active primarily during the twilight period, being matutinal (active during dawn), vespertine (biology), vespertine/vespertinal (active during dusk), or both. This is distinguished from diurnalit ...
behavior and may even appear in midday, but are mainly
nocturnal
Nocturnality is a ethology, behavior in some non-human animals characterized by being active during the night and sleeping during the day. The common adjective is "nocturnal", versus diurnality, diurnal meaning the opposite.
Nocturnal creatur ...
. They may be less active during the full moon. They have been described as "shy and excitable, and seldom bites when handled". They vocalize a shrill, high-pitched squeak when frightened. In laboratory studies, cactus mice average a running speed of .
Compared to other ''Peromyscus'' species, cactus mice have a lower metabolism. This is thought to be an adaptation to arid environments, and maintained by lower activity of the
thyroid gland. They may enter
torpor
Torpor is a state of decreased physiological activity in an animal, usually marked by a reduced body temperature and metabolic rate. Torpor enables animals to survive periods of reduced food availability. The term "torpor" can refer to the ti ...
when deprived of food in the winter, and food and/or water in the summer. Below , they enter torpor more slowly, which may partially explain their southern distribution. In the laboratory, onset of torpor was observed to occur within half an hour of food deprivation.
When dehydrated, they reduce eating to conserve water that would be expended during digestion.
They are important as seed predators and as prey items for other animals.
Reproduction
The mating habits of cactus mice are currently not well studied, but are inferred from other ''Peromyscus'' species to be promiscuous. They mate year around, but more so during warmer months. Unlike other muroids, male cactus mice have a simple penis, rather than a complex one, and females have two pairs of
teats, rather than three. The number of teats in the female cactus mouse correlates with the number of offspring they can raise in their arid environment.
Females mate after about two months, however, male sexual maturity age is unknown.
Relationship with humans

Cactus mice are ideal laboratory animals since they keep clean, live well in captivity, and have a high rate of productivity. They have been proposed for physiological and genetic studies.
There are no known negative effects on humans or human-related activities.
Specimens from Southern California have tested positive for hantavirus, however, infections in this species are likely incidental and localized, rather than a common reservoir.
[Journal of the Society Of Vector Ecologists, Volume 26, Issue 2, December 2001]
References
{{Taxonbar, from=Q1768203
Cactus mouse
Rodents of Mexico
Rodents of the United States
Fauna of the Southwestern United States
Fauna of the Baja California Peninsula
Fauna of the California chaparral and woodlands
Fauna of the Chihuahuan Desert
Fauna of the Colorado Desert
Fauna of the Sonoran Desert
Fauna of Gulf of California islands
Mammals described in 1858
Taxa named by Spencer Fullerton Baird
Taxonomy articles created by Polbot