The Cactus Deermouse (Peromyscus eremicus) is a species of low-desert mice with medium-length ears and medium-length tails. The dorsal color is grayish to ocherous and uniformly colored on the sides and along the center of the back (no dorsal stripe). The underside and feet are whitish. The tail is about as long as the body and is sparsely haired.

Technical Description: The head-and-body length (stretched out) is about 85 mm, the tail is about 100 mm, the ear is about 18 mm long, and the hind-foot is about 20 mm long, and they weigh about 20 g (females heavier than males). The tail is indistinctly bi-colored, and the hairs on tip are very short (2-4 mm).

Cactus Deermice look like all of the other "deer mice" (members of the genus Peromyscus) and can be difficult to identify with certainty. For the lay person, passing them off as "deer mice" is good enough.

For those concerned, consult range maps to ensure that this species is a possibility in the area, then rule out other possibilities by examining the ears and tail.

Around Las Vegas, the possibilities are Cactus Deermouse, Canyon Deermouse, North American Deermouse, and Pinyon Deermouse.

In the Cactus Deermouse, the ears are short, which rules out Pinyon Deermouse (ears more than 1-inch long). The tail is bi-colored, but the line between the dark and light is indistinct, ruling out North American Deermouse (distinct line). The tail is scantly clad with hairs, and the hairs on the tip of the tail are short (extending only 2-4 mm beyond the tip of the tail), ruling out Canyon Deermouse (which have hairy tails and the hairs extend about 8 mm beyond the tip of the tail).

The Cactus Deermouse (Peromyscus eremicus) is often the most common "deer mouse" or "field mouse" in the open Mojave Desert. Cactus Deermice live in lower elevation vegetation communities in the Lower (Creosote-Bursage Flats) and Upper Sonoran (Mojave Desert Scrub) life zones. They build nests under rocks, in old burrows of other animals, and in piles of dead vegetation. They sleep during the day and come out during the night to forage on seeds and vegetation. They also eat bugs and carrion when they can, and they happily raid camper's food.

Cactus Deermice are preyed upon by everything: snakes, owls, kit fox, large scorpions, lizards, and anything else that can catch them. They have high reproductive rates (lots of litters and lots of pups per litter), so they survive high predation rates.

All deer mice, including Cactus Deermouse, carry Hanta Virus, a potentially deadly disease that attacks the respiratory system with flu-like symptoms. Despite the occasional hysteria, it is difficult to contract hanta virus. I have handled thousands of Peromyscus, often in less than sanitary conditions, and I've never died or even gotten sick from hanta virus.