Coastal or northern rubber boa (Charina bottae)
The coastal rubber boa (Charina bottae) is a primitive snake in the boa family (Boidae) and has retained the club-like tail of its Erycine ancestors. The name Charina is from the Greek for graceful or delightful, and the name bottae honors Dr. Paolo E. Botta, an Italian ship's surgeon, explorer and naturalist.
The adult boa is 15-33 in (840 mm) long; newborns are typically 7.5-9 in (230 mm) long. The skin is often loose and wrinkled and consists of small, smooth. shiny scales, giving the snake a rubber-like look and texture. Colours are typically tan to dark brown with a lighter ventral surface but may be olive-green, yellow or orange. Newborns often appear pink and slightly transparent but darken with age. The boa has small eyes with vertically elliptical pupils and a short, blunt head, no wider than the body. The short, blunt tail closely resembles the shape of the head.
The rubber boa is the most northerly boa. It is native to much of the western USA, from the Pacific Coast east to western Utah and Montana, south to the San Bernardino and San Jacinto Mountains east of Los Angeles in California and north to southern British Columbia with an established population around Radium Hot Springs . Distribution is most spotty at the southern and eastern fringes of the range.It occurs from near sea level to @ 3,050 m (10,000 ft) (4,5). There have been rare sightings in Colorado and Alberta. The boa inhabits various habitat types from grassland, grassy savannas, meadows and patchy chaparral to deciduous and conifer forests and woodlands, forest clearings and high alpine settings. It usually lives near water, but also lives in riparian zones in arid canyons and sagebrush in some areas (5,8-10). Generally this snake is found in or under rotting logs or stumps, under rocks or in crevices, or under leaf litter, the bark of dead fallen trees or in burrows. It is less tolerant of higher temperatures than other snake species and cannot inhabit areas that are too hot and dry. It can live in areas that are quite cold, but prefers areas that provide adequate warmth, moisture and prey. It is thought to maintain a relatively small home range as many individuals are often captured in the same area year after year, but individuals may occasionally migrate due to competition lack of prey, or other pressures. Juvenile dispersal is not considered a migration.
Rubber boas are considered one of the most docile of the boa species and are often used to help people overcome their fear of snakes  . They never strike at or bite a human, but release a potent musk from their vent if they feel threatened. They are primarily nocturnal and probably crepuscular (active at dawn and dusk). Due to the temperature of the habitat, they hibernate during winter months in underground dens. They are very adaptable snake, being good climbers, burrowers and swimmers.Activity occurs mostly at night or dusk but also commonly occurs in daytime during mild cloudy weather. Most activity occurs from March to November.
The boas feed on young voles, mice, etc. When they encounter nestling mammals, they try to consume the entire litter if possible and fend off the mother with their tail, which often has extensive scarring. They also prey on snakes and lizards and their eggs and young and small birds and bats. They generally kills their prey by constriction prior to ingestion. Their predators are varied. Threatened boas curl into a ball, bury their head inside and expose their tail to mimic their head. This is thought to be a primary defense technique against predators, it is doubtful that this behavior is effective against large predators, such as raptors, coyotes, raccoons and cats. The best defence of rubber boas is their secretive nature.
Rubber boas are ovoviviparous and can have 2-8 young a year, but many females only reproduce every 4 years. Mating occurs soon after reemergence from hibernation in spring and young are born from August-November that year . The boa lives up to 26.5 years in captivity.
The total adult population size probably exceeds 10,000 and perhaps 100,000. This snake is secretive, but under appropriate temperature and moisture conditions it is locally quite common (8,9). It seems to be secure, due to its widespread occurrence in many areas that still provide suitable habitat. It is moderately vulnerable, but is not threatened in most of its range. Its Red List Category is Least Concern, due to the wide range, presumed large population and as it is unlikely to be declining fast enough for listing in a more threatened category. Its Global Short Term Trend is relatively stable due to the extent of occurrence, area of occupnacy, number of subpopulations and population size. The populations in southern California may be declining. Many populations are appropriately protected and managed in national and state parks and other protected areas.
Collins (13) did not recognize any subspecies. Stebbins (15) recognized 3 subspecies (bottae, utahensis, and umbratica). Stewart (4) recognized two subspecies (bottae and umbratica), with populations from Mt. Pinos and the Tehachapi Mountains, California, as intergrades between these subspecies. The southern rubber boa is sometimes classified as a subspecies (Charina bottae umbratica) (5). Nussbaum and Hoyer (12) showed that the subspecies utahensis is indistiguishable from subspecies bottae and regarded the concept "umbratica" as meaningless. Other scientists classify it as a separate species (Charina umbratica) from a few disjunct areas in the mountains of southern California (6,7,14,16,17). Rodriguez-Robles et al. (6) used mtDNA data to conclude that "umbratica is a genetically cohesive, allopatric taxon that is morphologically diagnosable" and "is an independent evolutionary unit that should be recognized as a distinct species, Charina umbratica." They acknowledged that a mixture of bottae and umbratica traits exists in populations in the Tehachapi Mountains and Mount Pinos, but interpreted this as persistent ancestral polymorphisms. They found no support to recognize utahensis as a valid taxon. The southern rubber boa is reportedly declining due to habitat loss and degradation (resort development, smog, logging, wood gathering) (11).
- 1. "All About The Rubber Boa Charina bottae, Natural History (and other info) of the Rubber Boa". All About The Rubber Boa Charina bottae. October 8, 2009.
- 2. "California Reptiles and Amphibians, Northern Rubber Boa". California Reptiles & Amphibians. February 23, 2009.
- 3. "Radium Hot Springs’ Remarkable Rubber Boa: A Species of Special Concern". Parks Canada Agency. October 4, 2004.
- 4. Stewart 1977
- 5. Stebbins 2003
- 6. Rodrigues-Robles, J. A., et al. 2001. Mitochondrial DNA based phylogeography of North American rubber boas, Charina bottae. Molecular Phylogenetics and Evolution. 18(2) 227–37.
- 7. Crother 2008
- 8. Nussbaum et al. 1983,
- 9. Brown et al. 1995,
- 10. St. John 2002
- 11. California Department of Fish and Game 1990
- 12. Nussbaum, R. and R. F. Hoyer. 1974. Geographic variation and the validity of subspecies in the rubber boa, Charina bottae. Northwest Science. 48:219-229.
- 13. Collins (1990)
- 14. Erwin (1974)
- 15. Stebbins (1985)
- 16. Crother et al. (2003)
- 17. Collins and Taggart (2009)
- Other References
- Hoyer, R. F. 1974. Description of a rubber boa (Chrina bottae) population from western Oregon. Herpetologica. 30:275-283.
- Hoyer, R. F. and G. R. Stewart. 2000. Biology of the rubber boa (Charina bottae), with emphasis on C. b. umbratica. Part I: Capture, size, sexual dimorphism, and reproduction. Journal of Herpetology. 34:248-354.
- Hoyer, R. F. and G. R. Stewart. 2000. Biology of the rubber boa (Chrina bottae), with emphasis on C. b. umbratica. Part II: Diet, antagonists, and predators. Journal of Herpetology. 34:354-360.
- Hoyer, R. All About the Rubber Boa. 2011.
- Klauber, L. M. 1943. The subspecies of the rubber boa, Charina. Trans. San Diego Soc. Natur. Hist. 10:83-90.
- Stebbins, R. C. 1955. A Field Guide to Western Reptiles and Amphibians, 2nd ed. Houghton, Mifflin, Boston.