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 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).

This species occurs in southwestern United States and northwestern Mexico. Its range extends from southern California and western and southern Arizona, south to the tip of Baja California and to southern Sonora, Mexico, including some islands along the Pacific Coast of Baja California (including Cedros) and in the Gulf of California (including Angel de la Guardia and Tiburón). It occurs at elevations from sea level to 2,070 m (Yingling 1982, Grismer 2002, Stebbins 2003).

Rosy boas occur in the southwestern United States and in adjacent areas of Mexico, specifically from Hanaupah Canyon (Death Valley area) in California south through Baja California, southwestern Arizona, and western Sonora, Mexico.

Three subspecies are traditionally recognized: Lichanura t. gracia, desert rosy boas (found from southern California to southwestern Arizona to northeastern Baja California), L.t. roseofusca, coastal rosy boas (found from coastal southwestern California into northern Baja California), and L.t. trivirgata, Mexican rosy boas (found from the extreme southwestern corner of Arizona into western Sonora, Mexico and southern Baja California). These subspecies designations have been repeatedly challenged. Spiteri (1991) decided that the two "subspecies" in California interbreed so freely that they could be lumped into a new subspecies, L. t. myriolepis. This designation has not been widely used. Wood et. al (2008) analyzed mitochondrial DNA in rosy boas across their range and suggested that two evolutionary species could be provisionally recognized: Charina trivirgata would encompass most of the USA portion of the ranges of L. t. gracia and L. t. roseofusca. Charina trivirgata would occur in southern San Diego County, California, extreme SW Arizona south of the Gila River, and through the Baja peninsula and NW Sonora, Mexico. Additional genetic and morphological studies may confirm or refute this arrangement.

Kluge (1993) placed rosy boas into the genus Charina along with rubber boas, Charina bottae due to shared characters; however, this arrangement has been questioned, and most recent checklists retain rosy boas in the genus Lichanura 

Biogeographic Regions: nearctic (Native )

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Global Range: (20,000-2,500,000 square km (about 8000-1,000,000 square miles)) The range extends from southern California and western and southern Arizona south to the tip of Baja California and to southern Sonora, Mexico, including some islands along the Pacific Coast of Baja California and in the Gulf of California, at elevations from sea level to 2,070 meters (6,790 feet) (Yingling 1982, Grismer 2002, Stebbins 2003).

United States

Origin: Native

Regularity: Regularly occurring

Currently: Present

Confidence: Confident

Type of Residency: Year-round

Continent: Middle-America North-America
Distribution: USA (S California, SW Arizona),  Mexico (Baja California, W Sonora)  orcutti: USA (California: San Diego County in California along the coastal Peninsular Ranges, northward into the Mojave Desert and eastward in the Sonoran Desert of California and Arizona; Arizona: areas north of the Gila River, except for individuals inhabiting the Gila Mountains.)  
Type locality: Cape San Lucas, Baja California

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).

Rosy boas are one of the smaller members of the family Boidae. Adults range in total length from 43 to 112 cm (17 inches to 44 inches). These are fairly heavy-bodied snakes with smooth scales. The tail is short, tapered, and slightly prehensile, with a blunt tip. The head shape is elongated, slightly broader then the neck and covered dorsally with small scales. The pupil is vertically elliptical. The dorsal scales are smooth, pitless, and occur in 33 to 49 rows in populations north of Mexico. Rosy boas have between 216 and 245 ventral scutes, 38 to 52 undivided subcaudals, and an undivided anal plate. There are no chin shields. In the mouth, each maxilla has 14 to 20 (mean 17) teeth. Male rosy boas tend to be smaller than females, have more prominent anal spurs, and tails averaging 14% of total body length. Females are larger, have shorter, less conspicuous anal spurs that barely break the skin's surface, and the tail averages 13% of total length.

The normal color pattern presents as three dark stripes against a lighter background. The stripes can be sharply defined or have irregular edges, and range from black or brown to reddish-brown, orangish, or rose in color. The background color ranges from gray, bluish-gray or tan to yellow, cream, or white. Spots of darker pigment may invade the lighter background in some local variants. Occasional specimens are unicolored and lack obvious striping. The chin, throat and venter ranges from cream to grayish white. The named subspecies have been defined by trends in coloration. Desert rosy boas tend to have well-defined stripes and lighter background color. Coastal forms are darker overall with less well-definded stripes, and Mexican rosy boas often have dark brown, sharp-edged stripes on a cream or yellowish background. However, much intergradation and variation occurs both between and within subspecies ranges. The name "rosy" was apparently derived from the pinkish ventral color of some specimens from the Baja peninsula; since this is atypical for the species, the more logical common name "three-lined boa" has been suggested.

Rubber boas (Charina bottae) are sympatric with rosy boas in parts of Southern California and might be confused with some of the more heavily pigmented rosy boas. Rubber Boas differ in having enlarged scales on the head and tend to be uniformly colored, without trace of striping.

Range length: 43 to 112 cm.

Average length: 76 cm.

Other Physical Features: ectothermic ; heterothermic ; bilateral symmetry

Sexual Dimorphism: female larger

Length: 107 cm

Holotype for Charina trivirgata
Catalog Number: USNM 15503
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1889
Locality: Colorado Desert, San Diego, California, United States, North America

Holotype for Charina trivirgata
Catalog Number: USNM 13810
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1884
Locality: San Diego, California, United States, North America

Syntype for Charina trivirgata
Catalog Number: USNM 15502
Collection: Smithsonian Institution, National Museum of Natural History, Department of Vertebrate Zoology, Division of Amphibians & Reptiles
Preparation: Ethanol
Year Collected: 1859
Locality: Cape San Lucas (= Cabo San Lucas), Baja California Sur, Mexico

Habitat and Ecology

Systems

• Terrestrial

Rosy boas live in dry shrublands, desert, and near-desert areas. They are found among scattered rocks and boulders or on talus slopes. Preferred habitat is often on south-facing hillsides at elevations from sea level to over 2,000 meters. Rosy boas are rarely found far from rock cover. They seem to prefer habitats near free water, such as canyon or desert streams, but are not restricted to such areas.

Range elevation: 0 to 2000 m.

Habitat Regions: terrestrial

Terrestrial Biomes: desert or dune ; chaparral ; scrub forest ; mountains

Aquatic Biomes: coastal

Other Habitat Features: caves

Comments: Habitats are diverse and include desert, arid scrub, brushland, sandy plains, rocky slopes, and chaparral-covered foothills, particularly where moisture is available, as around springs, streams, and canyon floors (but these snakes are not dependent on permanent water). This is a mainly terrestrial species, but it sometimes climbs into shrubs.

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).

Non-Migrant: Yes. At least some populations of this species do not make significant seasonal migrations. Juvenile dispersal is not considered a migration.

Locally Migrant: No. No populations of this species make local extended movements (generally less than 200 km) at particular times of the year (e.g., to breeding or wintering grounds, to hibernation sites).

Locally Migrant: No. No populations of this species make annual migrations of over 200 km.

Available information from coastal California and Arizona indicates that movements tend to be limited, and home ranges average less than 2 ha (see Diffendorfer et al. 2004).

Rosy boas eat rodents, nestling birds, bats, lizards, amphibians, and other snakes. The majority of the diet consists of small mammals such as kangaroo rats, deer mice, wood rats, and baby rabbits.  Rosy boas may slowly stalk their prey or ambush it from a hidden location. The prey animal is struck with great accuracy, then the snake's recurved teeth hold it securely while several body coils are wrapped around it, and it is then constricted. Once the captured prey is dead or incapacitated, the boa slowly releases the carcass by unwrapping its body and swallows the prey head first. Two prey animals can be constricted at a time, and one prey item can be consumed while another is still held in a body coil.

Animal Foods: birds; mammals; amphibians; reptiles

Primary Diet: carnivore (Eats terrestrial vertebrates)

Comments: Eats mainly small mammals and birds.

Rosy boas are predators that eat mainly nestling rodents in arid and semi-arid habitats. They undoubtedly serve as hosts for various parasites, but these are unreported in wild snakes.

Ecosystem Impact: keystone species

Rosy boas are undoubtedly killed and eaten by numerous predators, but no reports of predation in nature were found. Potential predators known to eat other snake species include carnivorous mammals (such as raccoons, ringtails, weasels, skunks, and coyotes), birds (hawks, shrikes), and other snakes, such as king snakes (Lampropeltis). Anti-predator behaviors in this snake include hiding the head in body coils, releasing a musky smelling substance from the cloaca, and biting. These snakes are usually rather docile and are not considered aggressive towards human handlers.

Anti-predator Adaptations: cryptic

Note: For many non-migratory species, occurrences are roughly equivalent to populations.

Estimated Number of Occurrences: 81 to >300

Comments: This species is represented by well over 100 occurrences or subpopulations. Yingling (1982) mapped some of them.

10,000 - 1,000,000 individuals

Comments: Total adult population size of this secretive snake is unknown but surely exceeds 10,000. This snake is common along the western slopes of the Sierra San Pedro Martir in Baja California (Welsh 1988).

Rosy boas, like all snakes, make good use of the vomeronasal (Jacobson's) organ for chemosensory input, facilitated by the extensible tongue. They also have appear to have good visual acuity, at least for close distances. Observations of courting animals suggests the use of chemical, tactile, and visual cues.

Communication Channels: visual ; tactile ; chemical

Other Communication Modes: pheromones

Perception Channels: visual ; tactile ; chemical

Comments: Snakes are inactive in cold temperatures and extreme heat. This species is usually most active at night.

The newborn young, from 18 to 36 cm long, are basically miniatures of the adults in shape and color pattern, though they may have more contrasting patterns (darker striping on lighter backgrounds) than their parents. Sex determination is genetic.

Development - Life Cycle: indeterminate growth

The average and maximum lifespan of rosy boas in the wild is unknown. Average lifespan for captive specimens ranges from 18 to 22 years, although some have been documented to live over 30 years.

Range lifespan

Status: captivity: 30 (high) years.

Typical lifespan

Status: captivity: 15 to 30 years.

Average lifespan

Status: captivity: 18 years.

Maximum longevity: 31 years (captivity)

Territorial behavior and male competition or fighting in wild rosy boas has apparently not been described. In courtship the male flicks his tongue over the female's body, and the female may tongue-flick the male in return. The male then slowly crawls over the female and strokes her posterior sides with erected anal spurs. If receptive, the female will turn her body to one side and elevate her tail. This allows the male to insert a hemipenis into her cloaca for fertilization.

Mating System: polygynandrous (promiscuous)

Courtship and mating occur from May through July and gestation requires 103 to 143 days. This is a viviparous species; females incubate fertilized eggs within their bodies and then give birth to live, independent young between August and November. Litters average 3 to 8 young, with a range of 1 to 14. Males apparently reach sexual maturity at 2 to 3 years of age, at a total length of 43 to 58 cm; females also mature in 2 or 3 years, at a length of about 60 cm.

Breeding interval: Females in the wild may breed only every other year; breeding frequency may depend on food supply and physical condition.

Breeding season: Breeding occurs from spring to early summer.

Range number of offspring: 1 to 14.

Average number of offspring: 5-8.

Range gestation period: 103 to 143 days.

Range age at sexual or reproductive maturity (female): 2 to 3 years.

Range age at sexual or reproductive maturity (male): 2 to 3 years.

Key Reproductive Features: iteroparous ; seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; fertilization ; ovoviviparous

A female rosy boa must acquire and store sufficient energy to provision her eggs (mostly in yolk) and then carry the developing embryos to birth. Once the young are born they are independent immediately, and the female's investment in that brood is over.

Parental Investment: pre-fertilization (Provisioning, Protecting: Female); pre-hatching/birth (Provisioning: Female, Protecting: Female)

Viviparous. Breeds May to June. Gestation lasts about 130 days (Behler and King 1979). Females give birth to 3-12 young, October-November (Stebbins 1985).

Barcode of Life Data Systems (BOLDS) Stats
Public Records: 0
Specimens with Barcodes: 1
Species With Barcodes: 1

The Bureau of Land Management in the State of California has this species listed as "sensitive" status (2008). Otherwise, populations are considered stable.

US Federal List: no special status

CITES: no special status

IUCN Red List of Threatened Species: least concern

United States

Rounded National Status Rank: N3 - Vulnerable

Rounded Global Status Rank: G4 - Apparently Secure

Reasons: Somewhat restricted range in southwestern North America; more than 100 occurrences; due to remoteness of habitat probably not greatly threatened rangewide, however, very threatened in some areas by overcollecting and highway mortality; highly sought after by collectors but somewhat resistant because difficult to find.

Intrinsic Vulnerability: Moderately vulnerable

United States

Rounded National Status Rank: N4 - Apparently Secure

Rounded Global Status Rank: G4 - Apparently Secure

Assessed as Least Concern (LC) on the IUCN Red List (1), and listed on Appendix II of CITES (3).

Population

Population Trend

Global Short Term Trend: Relatively stable (=10% change)

Comments: Overall, the extent of occurrence, area of occupancy, and number of subpopulations probably are relatively stable. Local declines seem to have occurred in some sites that are readily accessible to collectors. For example, populations have been greatly reduced in the vicinity of Route 85 in Organ Pipe Cactus National Monument (Parizek et al. 1996). However, this snake is still abundant in many remote areas of Organ Pipe Cactus National Monument and presumably elsewhere within the range (Parizek et al. 1996).

Global Long Term Trend: Increase of 10-25% to decline of 30%

Major Threats

Degree of Threat: BC

Comments: Overall, this snake is not very threatened. It often occurs in inaccessible, rugged terrain that affords natural protection from grazing and development, and a great deal of suitable habitat is available. Some local populations are threatened by overcollecting and road mortality (Parizek et al. 1996). This is a popular species in the pet trade, and collectors often target this snake; however, it is difficult to find and collect in quantity.

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).

Conservation Actions

Global Protection: Several (4-12) occurrences appropriately protected and managed

Comments: This species occurs in several national parks and monuments, state parks, and other protected areas.

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).

There are no known adverse effects of rosy boas on humans or human interests. If handled they may bite, but these inconspicuous snakes certainly do not seek confrontation with people.

Rosy boas may contribute to the control of rodent numbers but may not be sufficiently abundant to have a large impact. These boas are one of the most popular snakes in the pet trade due to their docile temperament, small size, low maintenance cost, and general ease of care. They have been collected throughout their range for the pet trade in the past, but these snakes are easily bred in captivity and most of the demand for these snakes can now be met by captive-bred animals.

Positive Impacts: pet trade ; controls pest population

Comments: This species formerly was transfered from the genus Lichanura to the genus Charina by Kluge (1993). Collins and Taggart (2002), Stebbins (2003), and Burbrink (2005) adopted this change, whereas Grismer (2002) did not. With the recognition of C. umbratica as a distinct species, and considering that both Charina and Lichanura contain fossil species, Charina and Lichanura are not monotypic sister taxa and so Crother (2008) treated Charina and Lichanura as separate genera.

Wood et al. (2008) examined mtDNA variation across the species range and identified three lineages that do not correspond to the traditionally recognized taxa of Lichanura. Wood et al. allocated the myDNA lineages to two species: Lichanura orcutti (California and Arizona) and L. trivirgata (extreme southwestern California, Baja California, Sonora (Mexico), and Arizona south of the Gila River. Wood et al. did not recognize any subspecies.