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 (Charina bottae). The rosy boa is native to the American Southwest, and Baja California and Sonora, Mexico.
These small attractive snakes attain a length of 17–30 in (though some specimens from the coast of California reach 3–3.5 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 name is 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 rosy 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. Interspace colors can be shades of light to dark gray, yellow, or tan.
The rosy boa is found in the southwestern United States in the states of California and Arizona, and northwestern Mexico in the states of Baja California and Sonora. In California, the rosy boa ranges throughout the Colorado and Mojave deserts and also occupies the coastal areas of Los Angeles, Orange, Riverside, and San Diego counties. In Arizona, the rosy boa occupies the Mojave Desert and the western areas of the Sonoran Desert. It is absent from the eastern and northern halves of the state. In Sonora, the rosy boa ranges from the border with the United States south throughout the Sonoran Desert to at least as far south as Ortiz. In Baja California, the rosy boa is almost ubiquitous ranging throughout the entire peninsula except in areas of extremely dry or rockless desert.
Rosy boas spend most of their lives concealed beneath rocks and in crevices to escape the elements and natural predators. Granite outcroppings are the most common geologic association inhabited by the rosy boa. Less often they are found in association with volcanic or other rock types. Only in rare places do rosy boas inhabit rockless environments. In areas with few rocks rosy boas will use rodent burrows for concealment.
Rosy boas' 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 rosy 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. Another reason 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 switches 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. When disturbed they usually roll into a compact ball with the head in the center. 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 nonvenomous. Their extreme docility and their attractive coloration have made rosy boas very popular with herpetoculturists.
Rosy boas bear live young, about six in a brood, with newborns about 30 cm (12 in.) in length.
The epithet trivirgata refers to the distinct three stripes that are characteristic of the species. The rosy boa is considered to be the only species within the genus Lichanura, but one researcher has placed it in the genus Charina with the rubber boa. Newer phylogenetic research supports the original arrangement but herpetologists are still not unified on rosy boa taxonomy. The subspecific designations are just as uncertain with many sources not accepting "arizonae" or "saslowi"
- Arizona rosy boa, Lichanura trivirgata arizonae Spiteri, 1991
- Desert rosy boa, Lichanura trivirgata gracia Klauber, 1931 – Ground color laced with well-defined pink, orange or tan longitudinal stripes.
- Coastal rosy boa, Lichanura trivirgata roseofusca Cope, 1868 – Ground color laced with blotchy reddish-brown longitudinal stripes.
- Baja rosy boa, Lichanura trivirgata saslowi Spiteri, 1987
- Mexican rosy boa, Lichanura trivirgata trivirgata Cope, 1861 – Ground color laced with pale, creamy broad longitudinal stripes.
Their generally docile temperament and small size make the rosy boa an ideal choice for a pet snake due to their easy care and small enclosure size (10–20 gallon). They are frequently captive bred, and readily feed on commercially available mice. Many color variations are available, including albinos as well as the different subspecies. With other species, such as corn snakes, milk snakes, and ball pythons, dominating the majority of the market, the popularity of rosy boas hasn't been as high as other species.
- Stejneger, L.H. and T. Barbour 1917. A Check List of North American Amphibians and Reptiles. Harvard University Press. Cambridge, Massachusetts. 125 pp. (Lichanura, p. 73.)
- Schmidt, K.P. and D.D. Davis. 1941. Field Book of Snakes of the United States and Canada. G.P. Putnam's Sons. New York. 365 pp. (Lichanura roseofusca, pp. 96–98 & Plate 8.)
- "Charina trivirgata". Integrated Taxonomic Information System. Retrieved 25 May 2006.
- Species Lichanura trivirgata at The Reptile Database