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http://www.eksperten.dk/spm/567872Scientific name: Boa constrictor imperator
Other common names
This is the boa subspecies most often encountered in captivity. There are in use a variety of different names all referring to this subspecies, including simply "boa constrictor." This form of boa may be referred to as the pet store boa constrictor, redtail boa, Colombian redtail boa, pet store redtail, and red-tailed boa constrictor. In fact many common boa constrictors do have a red tail, distinctly different in color than the rest of the body; however, the common name of "red-tailed boa" is also commonly applied to the South American boa constrictor, Boa constrictor constrictor, which typically has an even redder tail. The common boa has an extensive distribution in nature and many geographic names have come to be used to refer to this subspecies, including; Mexican boa, Sonoran desert boa, Yucatan boa, Central American boa, El Salvador boa, Nicaraguan boa, Panamanian boa and Colombian boa. Currently the Hog island boa is identified as a common boa constrictor, Boa constrictor imperator.
Size
This is a relatively slender elongate boa. The head is very distinct from the neck, the body is laterally compressed, the tail is long and strongly prehensile. Large specimens attain considerable bulk and may weigh 40-50 pounds. Adult specimens in most U.S. collections average about 4½-8 feet in total length. The maximum size of this form purportedly approaches 12 feet in total length, but the biggest we have seen were 9-10 feet long.
This is the tyrosinase-positive albino boa at two months of age. She is an entirely new form of albino, much more colorful than the more common t- albino boas. She was an unexpected birth in a clutch of 18 babies, the offspring of two normal boas that had never-before bred. One other of her female siblings in the clutch has a very unusual appearance, and exhibits some type of hypomelanistic condition combined with an axanthic condition. Some of her normal siblings are exceptionally beautiful common boa constrictors.
Distribution
This widespread boa constrictor subspecies occurs on the west coast of Mexico as far north as Hermosillo, Sonora, and on the east coast north to southern Tamaulipas. The species is widespread through the lower elevations of tropical southern Mexico. It is widespread and common in every country in Central America. From eastern Panama the range extends north in Colombia to the Sierra de Santa Marta, and south through coastal Colombia into Ecuador, south as far as Guayaquil. There at the southern extreme of the range, it intergrades with the Tumbes boa, Boa constrictor longicauda and Peruvian coastal boa, Boa constrictor ortonii.
Availability
Wild-caught animals are still collected and exported to the U.S. from several Central American countries, most recently including Guatemala, El Salvador, Nicaragua and Honduras. Wild-bred-captive-born babies also are exported to the U.S., some from Central America and many thousands from northern Colombia. Imported boas are commonly encountered in the pet trade, and occasionally seen at weekend reptile shows.
Boa constrictors have their own following of dedicated keepers and breeders who work with nothing else. U.S. captive-bred animals are readily available. Probably between one and two thousand common boas are now captive-bred and born in the U.S. each year. Excellent captive-bred specimens are available from professional breeders and serious hobbyists.. The species is offered for sale on many price lists, web sites, and classified advertising. Captive-bred animals are often encountered at weekend reptile shows.
Pattern variation
The typical common boa constrictor is a pale snake with a longitudinal series of 20 or more dark transverse bars spaced down the length of the back. These dark bars are each narrowest in the middle of the back and widest at the dorsolateral margin, where they incorporate a pale blotch on each side at the dorsolateral margin. In some boa constrictor patterns, the dark bars are connected along the sides to form a dark dorsal pattern on the back that outlines pale dorsal blotches that are oval or round. In other patterns, the dark dorsal bars are not connected to other dark elements of pattern. On the sides are a series of dark blotches with pale centers. Some blotches may contact the dark dorsal pattern. The pale areas of pattern are relatively evenly sprinkled with small black flecks and entire black scales. Generally, the patterns of boa constrictors from Colombia tend to include more bold black scales and even small black blotches on the sides than do the Central American specimens. The ventral surface of the neck and anterior body is ivory or pale gray, on the posterior half of the body the stomach becomes increasingly peppered with black smudges, flecks, and spots.
The tails are pale with large, oval, black-edged red blotches. This pattern continues onto the posterior body where the red pattern becomes more like bands. Continuing forward from the area of the vent, each successive pale interspace becomes wider and each red band becomes more narrow and less red, and in this manner the red pattern of the posterior body and tail melds into the dorsal pattern seen on most of the body.
This is an example of a t- albino boa at one year of age. They are beautiful and trim snakes, and t- albino common boas have now been bred three generations in captivity.
The head is predominantly pale with well-defined dark markings. There may be dark shading or barring on some of pale lip scales. There is a thin dark line on the top of the head from the internasals to the nape of the neck. Some specimens have two small lines over each eye. There is a small dark blotch below each eye and a dark horizontal line through each eye that continues as a well-defined dark postocular stripe.
There are numerous types of anomalous patterns reported to occur in boa constrictors, including a partial or complete loss of dark pattern, a reduction of the amount of dark pattern, or various conditions of dark striping. Some of these conditions have been demonstrated to be inherited as single recessive mutations, while the exact nature of the inheritance of many of the conditions is unknown. Some conditions of reduced dark pattern appear to be inherited as co-dominant traits or possibly as dilutions—more generations of breeding are necessary to determine with certainty the genetic basis of some of the types of patterns.
There are other anomalous conditions of pattern that have been demonstrated to be inheritable, including jungle boas (first bred in Europe), motley boas, first bred by Ron St Pierre of Florida, and arabesque boas, first bred by Steve Hammond.
Color variation
Common boa constrictors are primarily colored in shades of brown. The pale color on the head and most of the body varies from the palest browns, often with yellow or pink highlights, through grayish browns to medium browns. On some snakes the sides of the body are pale silver gray with pink or orange highlights. The dark markings are a rich chocolate brown to brownish black, sometimes with thin black margins. The pale dorsolateral spots are yellowish to ivory white. The pale coloration on the posterior body and tail is typically a medium ivory or pale yellowish tan. On dark-colored boas the red blotches on the tail and posterior body are typically dark brownish black with scattered dark oxblood-red scales; at the other extreme, the posterior red blotches of beautiful pale boas may be nearly solid bright red with thin black margins
There are numerous reported mutations of color in this population. Three types of albinism are known. The best-known lineage of albino boas, first bred by Peter Kahl of Maryland in 1993, is descended from a single wild-bred tyrosinase-negative (t-) albino male brought into the U.S. in the mid 1980s. There is a second lineage of t- albino boas descended from a different wild-caught female albino, first bred by Brian Sharp of Virginia. These two conditions of albinism are apparently due to different mutations, evidenced by the fact that when animals from these two lineages are bred together, the resulting offspring are all normal in appearance.
A third type of albino is now reported. In 1996, an apparent tyrosinase-positive (t+) albino boa was serendipitously born in the collection of Becky Hutchins of Texas. This animal and its siblings are now at VPI. Typical of other t+ albino snakes, this boa has dark-red eyes, and more color than the t- albino boas. Areas of black pattern are replaced with a medium purple-gray. The inheritance pattern of this type of albinism has not yet been determined in boas, but the condition is expected to be the result of a single recessive mutation.
There are several known wild-caught axanthic boa constrictors, in which the red color of the tail pattern is missing. Captive-breeding through two generations has demonstrated this condition to be inherited in the manner of a simple recessive trait. Peter Kahl has successfully combined the axanthic trait with the t- albino trait to produce an albino boa with no red coloration for which he has coined the descriptive name "snow boa."
There is a condition of hypomelanism in boas in which the tiny black flecks of melanin are missing, resulting in an overall paler animal. The black margins normally around the dark pattern are absent or greatly reduced, the condition is most obvious around the red blotches on the posterior body and tail. Many of these snakes have significantly reduced amounts of dark pattern. Two Arizona boa breeders, Rich Ihle and Jeff Gee, are primarily responsible for founding the lineages of hypomelanistic boas that are now available.
There is a lineage of unusually red boa constrictors, termed "blood boas, first bred by Ron St. Pierre of Florida. The normal pale brown coloration seen in most boas is replaced with distinctly reddish brown coloration in blood boas.
Boa constrictors are exotic and glamorous snakes, and there are few reptile hobbyists over the age of 40 that cannot claim to have possessed at least one boa at some point in their lives. We have had hundreds, and we remain captivated by these beautiful snakes. There is an observable wide variation of color and pattern--at one extreme of the range of variation, boa constrictors can be dark, dusky snakes; at the other extreme, they can be extraordinary pale snakes with pink and orange highlights. Of additional interest to keepers is their moderate size and calm demeanor.
It is this variation in the color and pattern of the common boa constrictors that particularly interests many boa breeders and keepers. Today there are numerous selective breeding projects ongoing, with some dedicated keepers working with third- and forth-generation boa constrictors, attempting to create some new appearance or establish some new mutation of this snake that fascinates them.
Common boa constrictors are beautiful snakes by every definition. This is a Colombian specimen, imported as an adult in 1978. Today adult boas constitute a smaller percentage of the total number of imported boas than was the case 20 years ago.
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