The Rosy Boa (Lichanura trivirgata) is a snake of the Boidae family, one of only two members of that family native to the United States. The other is the Rubber Boa (C. bottae). Rosy Boas are native to the American Southwest, and Baja and Sonora Mexico. These small attractive snakes attain a length of 39 in (1 meter) (though some species from the coast of California reach 4 feet) and a large adult has a body width about the diameter of a golf ball. Coloration in Rosy Boas is highly variable. The Common named was derived from the Rosy or Salmon coloration that is common on the belly of Rosy Boas originating from Coastal southern California and Baja Mexico. Most Boas do not have this ventral coloration but instead have a series of dark to orange spots on a light colored background. Almost all Rosy Boas have at least some trace of three longitudinal stripes, one down the center of the back, and two on the lower sides. The appearance of these stripes varies widely from extremely straight and having high contrast with the interspaces to extremely broken with almost no contrast with the interspaces. Stripe colors can be orange, maroon, rust, brown, or black. The interspaces range from shades of light to dark gray, yellow, or tan.
Rosy Boa's activity season follows local weather patterns; however, they are generally dormant during the winter, and active during the spring summer and fall. Like all snakes, they are dependent on external temperatures to promote such normal bodily functions as digestion and gestation. Throughout most of their range the winter is too cold for these functions and the Boas go into a dormant state called brumation. The spring is breeding season for Rosy Boas, resulting in their highest rate of activity. Most Rosy Boas are encountered in spring as they leave the security of their rock piles and crevices to seek mates. Other reasons Rosy Boas may be active on the surface of the ground is to find prey or new territory.
The surface activity of Rosy Boas can take place during any hour of the day, but during hot weather they are primarily nocturnal. In the spring, they are often abroad in the afternoon and early evening. In the late spring and summer, this activity period swithces to from dusk to late into the night. Because most populations of Rosy Boas live in exceedingly dry habitats, their activity is often highly moisture dependent. During dry periods they remain deep underground to assist in remaining hydrated. Recent Rainfall often results in a flurry of surface activity.
These snakes forage mainly for small mammals but have occasionally been known to take other prey items such as birds, and lizards. Pack Rats, baby Rabbits, Deer mice, and Kangaroo Rats make up a large portion of their diet. Rosy Boas are one of the slowest-moving species of snake in the world. They are unable to pursue prey and must either wait in ambush or stalk their meals. When a meal is within reach, usually a few inches, a Rosy Boa will strike with surprising speed and accuracy. Prey is secured with tiny rows of needle-sharp teeth, then suffocated through constriction.
Rosy Boas are extremely docile when encountered by humans. The species is not prone to bite in defense and when human bites have occurred they have usually been the result of a feeding response with a captive animal. All Rosy Boa bites are harmless. This extreme docility combined with their attractive coloration has made Rosy Boas very popular with herpetoculturists.