The boa constrictor (Boa constrictor) is a heavy-bodied lowland tropical snake ranging from northern Mexico through Central America to northern Argentina. Forcart (1951) treats the Genus Constrictor as a synonym of Boa with the single species constrictor. Surprisingly, the boa constrictor is closely related to three species of Malagasy boas. This biogeographic distribution of reptiles in both tropical America and Madagascar also occurs in iguanine lizards and sideneck turtles. The relationship is so close that Kluge (1991) recommends the transfer of the Malagasy boas to the Genus Boa. Because of various taxonomic conventions, he suggests the following names: Boa madagascarensis (Acrantophis madagascarensis) for the Madagascar ground boa, B. dumerili (Acrantophis dumerili) for Dumeril's boa, and B. manditra (Sanzinia madagascarensis) for the Madagascar tree boa.

Systematists currently recognize nine or ten poorly differentiated constrictor subspecies (Forcart 1951, Stimson 1969, Peters and Orejas-Miranda 1970, Langhammer 1983, Price and Russo 1991), three of which occur only on individual islands in the Gulf of Panama and the Lesser Antilles (Tables 1 and 2, Figure 1). The Mexican or Central American boa constrictor, imperator (Daudin 1803), is the northernmost race found from Mexico to northwestern South America. The common boa constrictor, B. c. constrictor Linnaeus 1758, is the most frequently imported subspecies, lives throughout Amazonian South America, and includes several "redtail" forms. B. c. ortonii Cope 1877, the Peruvian "redtail" boa constrictor, represents a restricted coastal population with a pale coloration but otherwise very similar to imperator. Langhammer (1983) suggests that it might best be relegated to the synonymy of imperator. B. c. occidentalis (Philippi 1873), the Argentine or pampas boa constrictor, and amarali, the Amaral's (or Brazilian or Bolivian) boa constrictor, occur to the south of constrictor as fairly widespread races.

The remaining subspecies have very restricted ranges and, in most cases, questionable statuses. B. c. orophias (Linnaeus 1758), the St. Lucia boa constrictor, and nebulosa Lazell 1964, the clouded or Dominica boa constrictor, occur on Caribbean islands. B. c. sabogae (Barbour 1906), the Taboga Island boa constrictor, is restricted to an island in the Gulf of Panama and represents a reddish color variant of the mainland imperator. Synonymy with imperator has been suggested, but supporting data have not yet been published (Langhammer 1983). B. c. melanogaster Langhammer 1983, the black-bellied boa constrictor, occurs in the upper Amazon rainforest of eastern Ecuador, but Price and Russo (1991) question the validity of this subspecies. B. c. longicauda Price and Russo 1991, the long-tailed boa constrictor, has a dark anerythristic coloration and proportionately long tail compared to other boa constrictor races. It has been reported only from Tumbes Province, Peru.

Several previously described races have been synonymized with adjacent subspecies. Peters and Orejas-Miranda (1970) include B. c. mexicana (Jan 1863) from Mexico, B. c. isthmica Garman 1883 from Panama, and B. c. eques (Eydoux and Souleyet 1842) from Peru in the synonymy of imperator. Zweifel (1960) synonymized the Mexican race sigma, the Tres Marías Islands boa constrictor described from María Madre Island by Smith (1943), with the mainland form imperator, though others have questioned this action by others (Langhammer 1983). Lazell (1964) refers B. c. diviniloqua (Duméril and Bibron 1844) to orophias, the St. Lucia boa constrictor.

Color Pattern and Meristic Variation

Considerable variation in color pattern exists both within and between subspecies (Table 1), especially with regard to insular and coastal forms. Many Boa constrictor populations exhibit reddish coloration of the tail and elsewhere (see below), but the redtail forms have no taxonomic status. Some amazing varieties, including albino and patternless forms, recently have been reported for boa constrictors (Barker 1993, Anonymous 1997, de Vosjoli 1997, Barnes and Dillon 1998). The imperator race tends to have a darker and less distinct color pattern than does constrictor. Hogg Island boa constrictors from cays off the Atlantic coast of Honduras exhibit pale patterns that may respond to light levels. The Taboga Island boa constrictor (sabogae) in Panama has an indistinct reddish brown pattern and most likely represents an aberrant population of imperator (Langhammer 1983). Some specimens of ortonii possess wine-red blotches on the rear of the body and are called Peruvian redtails. In the Lesser Antilles, the clouded boa constrictor (nebulosa) of Dominica has many narrow obscure dark blotches on a dusky ground color, while the St. Lucia boa constrictor (orophias) simply has a higher blotch count than does the mainland constrictor. Some individuals of constrictor from the Guianas and northeastern Brazil have wine-red blotches similar to those in some Peruvian boas and represent the other major group of redtails. The Argentine or pampas boa constrictor (occidentalis) is a small dark boa with the blotches forming a reticulate pattern. The Brazilian or Amaral's boa constrictor (amarali) in southern Brazil and Bolivia is virtually identical to constrictor, but it has a few more dorsal spots that differ slightly in shape from those in constrictor.

Table 1. Distribution and Dorsal Pattern of Subspecies of Boa Constrictor.

Subspecific range and pattern information on Boa constrictor extracted from Boulenger (1893), Stull (1935), Lazell (1964), Stimson (1969), Peters and Orejas-Miranda (1970), Schwartz and Thomas (1975), do Amaral (1977), Vanzolini et al. (1980), Langhammer (1983), and Price and Russo (1991).

SUBSPECIES	GEOGRAPHIC RANGE	PATTERN CHARACTERISTICS
amarali - Amaral's (or Brazilian or Bolivian ) boa constrictor	S and SE Brazil, SE Bolivia.	Middorsal head stripe without lateral projections, black rings around dorsal spots separated from one another, midbody spots with vertebral extensions directed toward head and tail, more than 21 saddle-shaped dorsal spots on body.
constrictor - common boa constrictor	Amazonian South America to Argentina and Paraguay; Trinidad, Tobago.	Middorsal head stripe without lateral projections, black rings around dorsal spots separated from one another, 14 to 22 subrectangular dorsal spots on body.
imperator - Mexican or Central American boa constrictor	N Mexico to NW South America; W of Andes in Colombia, Ecuador, and N Peru.	Middorsal head stripe with lateral projections, black rings around dorsal spots separated from one another, 22 to 30 dorsal spots on body.
longicauda - long‑tailed boa constrictor	Tumbes Province, Peru.	Middorsal head stripe with lateral projections, black rings around dorsal spots separated from one another, 19 to 21 dorsal spots on body, anerythristic dark coloration, tail length greater than 12% of total length in males.
melanogaster - black-bellied boa constrictor	E Ecuador.	Black rings around dorsal spots separated from one another, 20 to 21 dorsal spots on body, venter black in adults.
nebulosa - clouded or Dominica boa constrictor	Dominica, Lesser Antilles.	Middorsal head stripe without lateral projections, 31 to 35 obscure irregular transverse dorsal markings on clouded grey-brown ground of body.
occidentalis - Argentine or pampas boa constrictor	NW Argentina and Paraguay.	Middorsal head stripe without lateral projections, black rings around dorsal spots in contact with one another.
orophias - St. Lucia boa constrictor	St. Lucia, Lesser Antilles.	Middorsal head stripe without lateral projections, black rings around dorsal spots separated from one another, 27 to 31 saddle-shaped dorsal spots on body.
ortonii - Peruvian boa constrictor	NW coastal Peru.	Dorsal pattern inconspicuous, color pale and sandy.
sabogae - Taboga Island boa constrictor	Taboga Island, Panama.	Dorsal pattern inconspicuous, color dark reddish brown.

Table 2. Meristics of Subspecies of Boa Constrictor.

Subspecies	Ventral Plates	Caudal Plates	Midbody Scale Rows	Supra- Labials	Circum- Orbitals	Inter- Oculars	Lori- Labial Rows	Dorsal Spots	References
amarali	226‑237	43-52	71-79	20-24	15-20		1	>21	35,52,65
constrictor	231‑250	43-62	77-95	20-25	16-20	16-22	2-3	14-22	8,15,27,35, 36,52,56,65
imperator	225‑260	47-70	55-79	17-23	14-20	13-16	1-2	22-30	8,12,25,35,61, 63,64,65,70,72
longicauda	223‑247	50-67	60-76					19-21	54
melanogaster	237‑252	45-54	86-94					20-21	35
nebulosa	258‑273		59-69	19-21				31-35	35,36
occidentalis	242‑251	45	64-87	21-22	16-20	13-16	2-3	22-30	8,35,53
orophias	258‑288	55-69	65-75		14-19	16-18	1-2	25-31	8,35,36
ortonii	246‑252	46-59	57-72	19	19		1	15-19	11,35,54,58
sabogae	241‑247	49-70	65-67					------	2,35,65

Figure 1. Range Map of Boa Constrictor Subspecies and Other New World Boids (Modified from Savage 1966).

Savage (1966) recognizes three groups of New World boid genera: Young Northern (Charina, Lichanura), Middle American (Boa, Loxocemus, Ungaliophis), and South American (Corallus, Epicrates, Eunectes, Trachyboa, Tropidophis, Xenoboa). The range of the ten boa constrictor races encompasses the distributions of all Middle and South American genera except for the Caribbean forms. Boa constrictors occur from northern Argentina to northern Mexico.

I started with one female imperator from the Gulf Coast of Tamaulipas Province, Mexico, and one male and one female constrictor. Hence, the young I obtain are either constrictor or constrictor-imperator intergrades. The constrictor's show the influence of imperator in some characters, so they probably were imported from Colombia or Venezuela. The female constrictor is quite dark, while the male has a light tan ground color washed with considerable pink. The imperator possesses an unusual dark red and black pattern that appears to be characteristic of the Gulf of Mexico coastal populations. Neill and Allen (1962) describe the situation for Belíze populations as follows:

Elsewhere we mentioned the dark coloration of lowland boas, especially coastal ones, in British Honduras. We have since obtained 2 examples of a red phase from the mangrove swamps at Belíze. In these, all the darker elements of the pattern are dark red or cinnamon, and the background is pinkish. The specimens accord with the suggestion that reptiles from supratidal situations tend to be either unusually dark or reddish.

Boa constrictor imperator from coastal Tamaulipas, Mexico.

Two-year-old Boa constrictor constrictor born in captivity.

Natural History

Ranging from the pampas of western Argentina to both northern coasts of Mexico (Figure 1), the boa constrictor probably represents the commonest, widest ranging snake in the Western Hemisphere, if not the world. This heavy-bodied species primarily inhabits lowland tropical rainforest, but also occurs in arid pampas grasslands and scrub, mountainous tropical rainforest, coastal scrubs and marshes, thorn scrubs in the Yucatan, and second-growth forests on Caribbean islands and elsewhere in the range. The cryptic color pattern corresponds to a sit-and-wait style of predation and includes fine striping through the eye and its pupil to obscure the eye's outline. de Vosjoli (1998) observed a juvenile boa constrictor twitch its tail in an attempt to lure a lizard housed in an adjacent cage. Boa constrictors feed mostly on birds and mammals, but have been reported to take lizards also (Greene 1983). Body temperature of a free-ranging telemetered boa constrictor in Mexico averaged 26.4°C (79.5°F) with a range of 24 to 38.5°C (75.2 to 101.3°F) (McGinnis and Moore 1969), while another individual investigated in Panama maintained a body temperature from 24.4 to 29.4°C (75.9 to 84.9°F) over twelve days (Montgomery and Rand 1978). Basking temperatures of wild boa constrictors vary from 26 to 34°C (79 to 93°C) (Brattstrom 1965, Myres and Eells 1968).

Boa constrictors range from 40 to 55 cm (16 to 22 in.) at birth and can grow to one meter (39 in.) in the first year, one and a half (five feet) in the second, two (six and a half feet) in the third, and two and a half meters (over eight feet, females only) in the fourth year. Maturity typically does not occur until at least four years of age. Growth rate depends greatly upon the surrounding temperature and the amount of food given. Though literature reports of 4 to 5.5 m (13 to 18 ft.) exist (Greene 1983), average size attained in most populations and in captivity is considerably less. For the probable Colombians in this colony, females reach average maximum sizes of 2.4 m (94 in.) and 10.4 kg (23 lb.), while males average 1.9 m (75 in.) and 5 kb (11 lb.) (Figures 3 and 4). A mature imperator female from northern Mexico only reached 1.9 m (74 in.) and 5.4 kg (12 lb.). Growth virtually stops by the third year in males and the fifth year in females. The Growth section provides more detailed biometric data. Maximum size may vary geographically with smaller boa constrictors occurring in northern Mexico and Argentina, while larger ones are found in Amazonian South America. The length-weight relationship for colony animals estimates that an 18-foot boa would weigh better than 300 lbs. The only other large boids with such heavyset bodies are the green anaconda and blood python. Maximum lifespan reported in the literature is at least forty years (Bowler 1977, Huff 1980). The oldest individuals in this colony have reached the low twenties.

Literature information on boa constrictor reproduction is spotty and largely anecdotal. The mating period extends from December to March in Trinidad (Mole and Ulrich 1894, Mole 1924). Females ovulate large 2-3 inch yolked eggs. "Placentation" occurs in boa constrictors and represents a process by which oxygen, carbon dioxide, water, and perhaps other small molecules are exchanged between the maternal and neonatal blood streams. The energy used for development probably comes exclusively from the yolk sac. Gestation appears to last from five to six months in Colombia (Otero de la Espriella 1978). Litters have been obtained during August in Belíze (N=2, Neill 1962) and from November to February in Peru (N=4, Dixon and Soini 1986). The reproductive cycle may vary geographically. Six Mexican and Central American boa constrictor litters averaged 17.8 young with a range of 10 to 36, while six South American (Trinidad and Peru) litters had a mean of 30.3 and range from 6 to 63 (Fitch 1985). Otero de la Espriella (1978) gives a range of 40 to 80 young per litter in Colombia. The higher mean litter size in South America may reflect variation in size of the reported females. Hoover (1936) described a Central American female that gave birth to two live young and 13 leathery "eggs," two of which produced viable young. Boa constrictors may often produce infertile eggs with solid yolks or eggs with partially or fully developed stillborn young. The membrane of such eggs usually becomes thickened, translucent, and tough compared to the clear, delicate membrane containing a viable neonate.

Use by Man

The boa constrictor today represents one of the most heavily exploited reptile species. Dodd (1986, 1987) reports on legal importation of snakes into the United States. From 1977 to 1983, over 113000 live boas were imported; this amounted to nearly half of all the imported snakes listed for protection by the Convention on International Trade in Endangered Species of Wild Fauna and Flora. Live imports decreased 97 percent from 1979 to 1983 as more animals were used for production of ornamental leather. In 1983, 6572 whole boa constrictor skins, 1714 large leather pieces such as briefcases, and 165843 small pieces, mostly shoes, were brought into the United States. The only other snake species that supplies more skins and leather is the reticulated python (Python reticulatus). Though Otero de la Espriella (1978) describes a culture operation for boa constrictors in Colombia, the vast majority of imports must arise from natural populations whose status is completely unknown.