Rosy boa  (Charina trivirgata)

The rosy boa is an attractive snake, usually noted for its pattern of three wide, black, brown, reddish-brown or orange stripes that run along the body (4) (5). The exact colouration varies between the four recognised subspecies: the coastal rosy boa (Charina trivirgata roseofusca), the desert rosy boa (Charina trivirgata gracia), the mid-Baja rosy boa (Charina trivirgata saslowi) and the Mexican rosy boa (Charina trivirgata trivirgata) (6). The coastal rosy boa generally has pale rose, deep tan or orange uneven stripes with almost ragged edges against a grey background. The desert rosy boa also has a grey background, but with brown to russet stripes (6). The mid-Baja rosy boa has well-defined orange to russet stripes against a steal grey colour, while the Mexican rosy boa, the darkest of the four races, has chocolate to nearly black stripes that contrast greatly with the cream to pale tan background (6).

The body of the rosy boa is covered with smooth, shiny scales, and the eyes are small, with vertical pupils (2). The head is slightly larger than the neck, and the fairly long, thick tail comes to a blunt point. Two small claw-like spurs at the base of the tail are vestigial legs, a feature retained from its lizard ancestor (2).

The rosy boa occurs in the south-western United States and north-western Mexico (1), where the four subspecies differ in their distribution. The coastal rosy boa ranges from south-eastern California to north-western Baja California, while the desert rosy boa is found from south central California to central western Arizona. The mid-Baja rosy boa is found, as its name suggests, in central and southern Baja California, and the Mexican rosy boa inhabits north-western Sonora, south central Arizona, Baja California, and Isla Cedros, located off the west coast of Baja California (6).

The rosy boa can be found in a wide range of habitats, including desert, scrubland, sandy plains, and rocky slopes, from sea level up to an elevation of 2,070 metres (1). It is typically found in areas where there is sufficient vegetation and rocky cover to provide shelter (7), and although not dependent on permanent water, it is often found around springs and streams (1), as this attracts the birds and small mammals on which it feeds (4).

The rosy boa is a secretive (1), burrowing snake, which spends the majority of its time hidden beneath rocks and in crevices (5) (7), particularly during periods of extreme heat (2), and during winter in the colder parts of its range when it hibernates (5). Most activity takes place during the night (7), when it moves slowly across the ground, sometimes climbing into low shrubs (2).

Like other snakes in the Boidae family, the rosy boa is a powerful constrictor, making it a formidable predator. When its prey (a small mammal, bird or lizard), is within range, the rosy boa strikes out in a sudden, explosive motion (2). Grabbing the prey with its backward-curved teeth, the rosy boa quickly coils its muscular body around the animal and squeezes until its prey either suffocates, or its heart is too restricted to pump blood (2) (5). When the prey is dead, the rosy boa proceeds to swallow its victim whole (2).

Despite the deadly predatory skills of the rosy boa, this snake is still a desired prey item for a number of other animals, including owls, coyotes and kit foxes (7). It does, however, have a tactic it employs to try and avoid being the victim. When attacked by a predator, it will roll up into a ball, with its head in the centre. The blunt tail is thought to be a way of luring predators into attacking the wrong end of the snake (4), and also deters predators by releasing a foul-smelling musk from glands near the base of the tail (2).

The rosy boa mates in May and June, with between six and ten live young being born after a 130 day gestation period, around October and November (2). This snake is estimated to live for between 15 and 22 years (2).

The rosy boa is not currently considered to be threatened with extinction, although certain populations may be negatively impacted by over-collection and road mortality (1). Its attractive patterning makes it a popular species in the pet trade and it is therefore a target for collectors. However, its secretive habits make it difficult species to find and collect in any great quantity, and most rosy boas in the pet trade are captive bred, and therefore do not pose a threat to the survival of this species in the wild (1). The fairly inaccessible and rugged habitat of the rosy boa also gives this species some natural protection from habitat degradation, in the form of grazing or development, which threatens the survival of many other species (1).

The listing of the rosy boa on Appendix II of the Convention on International Trade in Endangered Species (CITES) means that any international trade in this species should be carefully monitored, giving this species some protection from the threat of over-collection from the wild (3). Furthermore, in addition to the natural protection this species' rugged habitat affords, the rosy boa can also be found in a number of national parks and other protected areas (1).

To help conserve snakes and other reptiles visit:

• International Reptile Conservation Fund:
  www.ircf.org

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk