Geography 316:  Biogeography    
In progress 12/16/2003

The Biogeography of the Rosy Boa (Lichinura Trivirgata).

by Cortland Marcelli, student in Geography 316  Fall 2003

Thank you for visiting our site. This web page was written by a student in Geography 316: Biogeography and edited by the instructor, Barbara Holzman, PhD.  All photos and maps are posted with specific copyright permission for the express use of education on these web pages. The students have tried to be as accurate as possible with the information provided and sources and references are cited at the end of each page.

Species Name:  Lichinura trivirgata

Kingdom:  Animalia
Lichinura trivirgata
Description of Species:

        The rosy boa is part of a large family of snakes that include all five of the world's giant snakes.  They have flexible jaws found in more advanced families but also retain a pelvic girdle, vestigial hind limbs, which are inherited from their lizard ancestors (Schmidt 2003).  Boas also have two functional lungs instead of one.  There are only two species of boas found in North America, one of which is the rosy boa, Lichinura trivirgata (Schmidt 2003).



The rosy boa is related to the boa constrictor and the anaconda, yet it only gets as long a 3 feet in length, one of the smallest members of the boa family (Flank 1996).  The skin of the rosy boa includes vertical stripes that run parallel with the earth’s surface, alternating gray and reddish brown colors.  These colors are great camouflage because they match the colors of their habitats.  They inhabit places with rocky outcrop in order to protect themselves from other predators.  Because the rosy boa operates within a narrow temperature range, the Southern United States and parts of Mexico are the idea habitat for them.  Arid semi-desert grasslands are the best habitat for the rosy boa to subsist and feed upon mice and lizards (Flank 1996).  They kill their prey by constriction. 

Nocturnal behavior is predominant during the late spring and summer months and more diurnal activity during the winter months (Risen 1999).   Hibernation usually lasts until early March.  The rosy boa uses the spring and summer months to absorb heat and capture prey, and to conserve energy to prepare itself for the coming winter season.  It is in the winter that the rosy boa restricts its activity in order to survive the winter months.  Mating season is during the summer, usually between May and July (Risen 1999).  In October or November, about 130 after conception, 6 to 10 young are born.  Hatchlings are usually 10 to 12 inches in length.  Boas are ovoviviparous (MW 2003), which means that the eggs develop inside the females are surrounded by a membrane instead of a hard shell.


It is common knowledge that all living things are a result of evolution.  Evolution is a process that allows species to change over time in order to adapt to changes in their environment, sometimes producing entirely new species (Flank 1997).  Evolution is driven by natural selection, where only the fittest will survive to reproduce successfully.  Therefore, those species that reproduce can pass on their traits to their offspring. 

Not much is known about the evolution of snakes because of the delicacy of their skeletons.  Most paleontologists’ research has revealed that reptiles evolved from a large group of ancient amphibians known as Labrynthodonts. (Flank 1997)  Evolution of snakes occurred around the end of the Mesozoic (250-65 mya), beginning of the Cenozoic era (65mya) (Greene 1997).  This is around the time when assortments of habitats were developing as a result of different latitudinal locations of the continents.  Differing climates and altitudes resulted in a divergence of species because, in order to survive, different species would need to adapt to the environment.  This is a good example, showing that species with the better traits survive and reproduce, and pass on those “fitter” traits to their offspring.  Reptiles advanced beyond the amphibian because of the development of the shelled egg, which freed the reptiles from returning to the water as adults for reproduction (Flank 1997).  This adaptation would eventually lead to the oviparous (live bearing young), rosy boa.

A small, lizard-like animal known as Hylonomus was found inside petrified tree stumps in Nova Scotia.  This is the oldest fossil recognized as a reptile (Flank 1997).  This animal resided on Pangea, the super continent.  When this super continent broke apart due to movement of plate boundaries, landmasses became more distinct in climates and terrain (McKnight 2002).  This movement led to noticeable consequences for the evolution and distribution of modern snakes.

        A group of very ancient reptiles known as the Cotylosaurs are believed by paleontologists to be ancestral to all of the reptile families alive today.  They first appeared during the Permian, the period of time that led to the rise of the dinosaurs.  Divergence of the Cotylosaurs led to three distinct groups of reptiles:  Anapsids are the earliest and would eventually become what is known today as the turtle.  Later, another group of Cotylosaurs, known as Synapsids, went on to evolve into the modern mammals.  The third group of reptiles, the Diapsids, branched out to produce the dinosaurs, as well as the modern lizards and snakes (Flank 1997). 

Snakes and lizards share a number of distinct features in the composition of their skull; both, for example, possess a moveable quadrate bone at the back of the jaw, and both are lacking the quadratojugal bone at the rear of the skull (Flank 1997).  Some herpetologists theorize that an ancient group of monitor-like lizards began burrowing through loose earth and over millions of years lost their limbs and external ears to burrow more efficiently.  They would later evolve protective covering for the eyes.  This animal would soon develop a legless mode of locomotion and would eventually be known as the snake (Greene 1997).  Even if this theory is not true, the first of the modern terrestrial snakes to appear seem to have been relatives of the living boids, or boas and pythons.  The rosy boa has two claw-like spurs near its vent, attached to bones inside its body.  These anal spurs are vestigial hind legs inherited from their lizard ancestors (Greene 1997).



Humans are greatly impacting the decrease in rosy boa populations because of the creation of roads, habitat fragmentation, and urbanization.  Another contributing factor to the decline of the rosy boa populations is their increase in popularity in the pet trade (Wood 2002).  The rosy boa is listed as a sensitive species by the National Park Service and is protected by the state of California (NPS 2003).  These impacts are escalating and will continue to degrade habitat that is essential for the conservation and preservation of this species.

The rosy boa can be seen throughout the semi-arid and arid regions of southwestern North America, ranging from southern California and western Arizona in the United States, on southward to Baja California and western Sonora in Mexico (Melli 2003).  This snake cannot survive in extremely cold areas.  They reside in warmer areas, usually at lower elevations.  Snakes are cold-blooded creatures, so they need solar radiation to absorb warmth.  When they have absorbed enough warmth from the sun, rosy boas hide under rocky substrates until the evening when they hunt for their food.  Coastal sage scrub, chaparral, and desert environments are the ideal habitats for this species (Melli 2003).  These snakes have been sighted in the Argus Range and Darwin Hills near Death Valley, in the high-desert mountain ranges south through the Mojave Desert, in the coastal region of southern California, in the peninsula of Baja California and the mainland, to western Arizona and the rocky hillsides of Kingman, and many other places (Perrett 2002). Because they like to reside in remote areas, it is difficult to accurately account for the number of rosy boas and how vastly they are distributed. 

Other interesting issues:

Snakes have inhabited the earth for a long time.  The rosy boa is one of the oldest snakes and obviously encompasses desired traits since they are still around today.  Although many snakes could not survive during the years following the break up of Pangea, those that were selected to have the superior traits were able to pass on their traits to their young for millions of years after.  It is true that the rosy boa is federally protected in California, and the decline in their population is probably a result of human impacts, such as urbanization, not because of lacking the desired traits to survive in their habitats.

The rosy boa is currently a Federal Special Concern species (Melli 2003).  It is very rare now and is protected from international trade by CITES (Melli 2003).  Because of urbanization, many natural habitats have been destroyed, including the habitat of the rosy boa.  Humans are the rosy boa’s greatest threat.  There are not many conservation programs for snakes, most likely because of the negative attitudes toward them.  The rosy boa is so passive and beautiful and should be more appreciated.  All species are interconnected and interdependent.  We all have are place here on earth, so we need to learn to coexist.  Otherwise, we will loose vital species necessary for the web of life to continue here on Earth.  


  1. Flank, Jr., Lenny.  (1996) An Owner’s Guide To A Happy Healthy Pet, The Snake.  Howell Book House.  pp. 28.
  1. Flank Jr., Lenny. (1997) Snakes: Their Care and Behavior.
  1. Greene, Harry W. (1997) Snakes The Evolution of Mystery in Nature.  University of California Press, CA. pp. 267-284.
  1. McKnight, Tom L. (2002) Physical Geography.  Prentice-Hall, Inc, NJ. pp. 398-399.
  1. Melli, Jim.  The San Diego Natural History Museum. (2003) “Field Guide to Rosy Boas”.
  1. Merriam-Webster on-line Dictionary. (2003)  “Ovoviviparous”.
  1. National Park Service (2003).  Mojave National Reserve: Snakes.
  1. Perrett, Jordan A. (2002). Natural History:  Range
  1. Risen, Larry A. (1999)  “Natural History.”
  1. Schmidt, Ph.D., Martin C. (2003) “Snakes of North America”.
  1. Wood, D.A. (2002). Intraspecific Phylogeny of the Rosy Boa (Charina Trivirgata): Implications for Phylogeography, Taxonomy, and Conservation.  Master's Thesis. Department of Biology, San Diego State University


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