Animal Diversity Web

Ge­o­graphic Range

Boa con­stric­tor is an ex­clu­sively New World species which has the largest dis­tri­b­u­tion of all neotrop­i­cal boas. Boa con­stric­tors range from north­ern Mex­ico south through Cen­tral and South Amer­ica. In South Amer­ica the range splits along the Andes moun­tains. To the east of the Andes, B. con­stric­tor is found as far south as north­ern Ar­gentina. On the west side of the moun­tains, the range ex­tends into Peru. Boa con­stric­tors are also found on nu­mer­ous is­lands off the Pa­cific coast and in the Caribbean. Is­lands in­cluded in the boa con­stric­tor range are: the Lesser An­tilles, Trinidad, To­bago, Do­minica, and St. Lucia. Some is­lands off the coast of Be­lize and Hon­duras are also in­hab­ited by this species. (Chiar­aviglio, et al., 2003; Mat­ti­son, 2007; O'Shea, 2007; Stafford, 1986)

• Biogeographic Regions
• nearctic
  • native
• neotropical
  • native

Habi­tat

Boa con­stric­tors oc­cupy a va­ri­ety of habi­tats. Pri­mary habi­tat is rain­for­est clear­ings or edges. How­ever, they are also found in wood­lands, grass­lands, dry trop­i­cal for­est, thorn scrub, and semi-desert. Boa con­stric­tors are also com­mon near human set­tle­ments and often found in agri­cul­tural areas. Boa con­stric­tors are com­monly seen in or along streams and rivers in ap­pro­pri­ate habi­tats. Boa con­stric­tors are semi-ar­bo­real, al­though ju­ve­niles tend to be more ar­bo­real than adults. They also move well on the ground and can be found oc­cu­py­ing the bur­rows of medium-sized mam­mals. (Mat­ti­son, 2007; Mont­gomery and Rand, 1978; O'Shea, 2007; Stafford, 1986)

• Habitat Regions
• tropical
• terrestrial

• Terrestrial Biomes
• savanna or grassland
• chaparral
• forest
• rainforest
• scrub forest

• Aquatic Biomes
• rivers and streams

• Other Habitat Features
• agricultural
• riparian

• Range elevation

  0 to 1,000 m

  0.00 to ft

Phys­i­cal De­scrip­tion

Boa con­stric­tor has long been fa­mous as one of the largest species of snake. In re­al­ity, boa con­stric­tors are fairly mod­est-sized boids and are dwarfed by the other com­peti­tors for this title. The max­i­mum length re­ported in B. con­stric­tor was slightly over 4 me­ters. In­di­vid­u­als are gen­er­ally be­tween 2 and 3 me­ters in length, al­though is­land forms are com­monly below 2 me­ters. Within pop­u­la­tions, fe­males are usu­ally larger than males. How­ever, the tails of males may be pro­por­tion­ally longer than those of fe­males be­cause of the space taken up by the hemipenes. Boa con­stric­tor col­oration and pat­tern are dis­tinc­tive. Dor­sally the back­ground color is cream or brown that is marked with dark "sad­dle-shaped" bands. These sad­dles be­come more col­or­ful and promi­nent to­wards the tail, often be­com­ing red­dish brown with ei­ther black or cream edg­ing. Along the sides, there are rhom­boid, dark marks. They may have smaller dark spots over the en­tire body. The head of a boa con­stric­tor has 3 dis­tinc­tive stripes. First is a line that runs dor­sally from the snout to the back of the head. Sec­ond, there is a dark tri­an­gle be­tween the snout and the eye. Third, this dark tri­an­gle is con­tin­ued be­hind the eye, where it slants down­ward to­wards the jaw. How­ever, there are many vari­a­tions on ap­pear­ance. At least 9 sub­species are cur­rently rec­og­nized by some au­thor­i­ties, al­though many of these are poorly de­fined and fu­ture re­search will un­doubt­edly mod­ify this tax­on­omy. Cur­rently ac­knowl­edged sub­species in­clude: B. c. con­stric­tor, B. c. orophias, B. c. im­per­a­tor, B. c. oc­ci­den­talis, B. c. or­tonii, B. c. sabo­gae, B. c. ama­r­ali, B. c. neb­u­losa (Do­mini­can boa, re­cently el­e­vated to full species), and B. c. long­i­cauda. Most of these sub­species are dis­tin­guished largely by their range rather than ap­pear­ance, but re­gional (sub­spe­cific) vari­a­tion in form, size, and col­oration does occur. (Chiar­aviglio, et al., 2003; Mat­ti­son, 2007; O'Shea, 2007; Stafford, 1986)

As in most mem­bers of the fam­ily Boidae, boa con­stric­tors pos­sesses pelvic spurs. These are hind leg rem­nants found on ei­ther side of the cloa­cal open­ing. They are used by males in courtship and are larger in males than in fe­males. Males pos­sess hemipenes, a dou­ble-pe­nis, of which only one side is com­monly used in mat­ing. Al­though heat-sens­ing pits are com­mon in Boidae, they are ab­sent in B. con­stric­tor. Thus, this species is pre­sumed to have no spe­cial­ized ther­mosen­sory abil­i­ties. The teeth of boa con­stric­tors are aglyp­hous, mean­ing they do not pos­sess any elon­gated fangs. In­stead, they have rows of long, re­curved teeth of about the same size. Teeth are con­tin­u­ously re­placed; par­tic­u­lar teeth being re­placed at any one time al­ter­nate, so that a snake never loses the abil­ity to bite in any part of its mouth. Boas are non-ven­omous. Boa con­stric­tors have two func­tional lungs, a con­di­tion found in boas and pythons. Most snakes have a re­duced left lung and an ex­tended right lung, to bet­ter match their elon­gated body shape. (Mat­ti­son, 2007; O'Shea, 2007; Pough, et al., 2004)

• Other Physical Features
• heterothermic
• polymorphic

• Sexual Dimorphism
• female larger

• Range length

  1 to 4 m

  3.28 to 13.12 ft

• Average length

  2-3 m

  ft

De­vel­op­ment

Fer­til­iza­tion is in­ter­nal, with mat­ing fa­cil­i­tated by the pelvic spurs of males. Boa con­stric­tors are ovo­vi­vip­a­rous; em­bryos de­velop within their moth­ers' bod­ies. Young are born live and are in­de­pen­dent soon after birth. New­born boa con­stric­tors re­sem­ble their par­ents and do not un­dergo any meta­mor­pho­sis. As in other snakes, boa con­stric­tors shed their skins pe­ri­od­i­cally as they age, al­low­ing them to grow and pre­vent­ing the scales from be­com­ing worn. As a boa grows, and its skin is shed, its col­oration may grad­u­ally change. Young snakes tend to have brighter col­ors and more con­trast be­tween col­ors, but most changes are sub­tle. (Mat­ti­son, 2007; O'Shea, 2007; Pough, et al., 2004; Stafford, 1986)

Re­pro­duc­tion

Males are polyg­y­nous; each male can mate with mul­ti­ple fe­males. Fe­males may also have more than one mate in a sea­son. Fe­males are usu­ally widely scat­tered and court­ing males must in­vest en­ergy into lo­cat­ing them. Most fe­male boa con­stric­tors do not ap­pear to re­pro­duce an­nu­ally. Usu­ally about half of the fe­male pop­u­la­tion is re­pro­duc­tive each year. Fur­ther­more, fe­males likely be­come re­pro­duc­tive only when they are in good phys­i­cal con­di­tion. While a higher per­cent­age of males seems to re­pro­duce each year, it is likely that the ma­jor­ity of males also do not re­pro­duce an­nu­ally. (O'Shea, 2007; Stafford, 1986)

• Mating System
• polygynandrous (promiscuous)

Boa con­stric­tors gen­er­ally breed dur­ing the dry sea­son, usu­ally from April to Au­gust, though the tim­ing of the dry sea­son varies across their range. Ges­ta­tion lasts for 5 to 8 months de­pend­ing on local tem­per­a­tures. The av­er­age lit­ter has 25 young but can be any­where from 10 to 64 young. (Bertona and Chiar­aviglio, 2003; Chiar­aviglio, et al., 2003; Mat­ti­son, 2007; O'Shea, 2007; Stafford, 1986)

• Key Reproductive Features
• iteroparous
• seasonal breeding
• sexual
• fertilization
• viviparous

• Breeding interval

  Females perhaps every other year, or less often, depending on condition.

• Breeding season

  Breeding occurs during the dry season (April-August), birth occurs 5-8 months later.

• Range number of offspring

  10 to 64

• Average number of offspring

  24 (in <<B.c. occidentalis>>)

• Range gestation period

  5 to 8 months

• Average time to independence

  after only a few minutes

• Average age at sexual or reproductive maturity (female)

  2-3 years

• Average age at sexual or reproductive maturity (male)

  2-3 years

Ma­ter­nal in­vest­ment in young is con­sid­er­able and re­quires the mother to be in good phys­i­cal con­di­tion. Since young boa con­stric­tors de­velop within the mother's body, they are able to de­velop in a ther­moreg­u­lated, pro­tected en­vi­ron­ment and they are pro­vided with nu­tri­ents. Boa con­stric­tor young are born fully de­vel­oped and are in­de­pen­dent within min­utes of birth. Male re­pro­duc­tive in­vest­ment is largely spent in find­ing mates. (An­drade and Abe, 1998; O'Shea, 2007; Stafford, 1986)

• Parental Investment
• pre-fertilization
  • provisioning
  • protecting
    • female
• pre-hatching/birth
  • provisioning
    • female
  • protecting
    • female

Lifes­pan/Longevity

Boa con­stric­tors are po­ten­tially long-lived, per­haps av­er­ag­ing around 20 years old. Cap­tive boas tend to live longer than wild ones, some­times by as much as 10 to 15 years. (O'Shea, 2007; Stafford, 1986)

• Range lifespan
  Status: wild

  30 (high) years

• Range lifespan
  Status: captivity

  40 (high) years

• Average lifespan
  Status: wild

  20 years

• Typical lifespan
  Status: captivity

  25 to 35 years

Be­hav­ior

Boa con­stric­tors are soli­tary, as­so­ci­at­ing with con­specifics only to mate. How­ever, Do­mini­can pop­u­la­tions which will oc­ca­sion­ally den to­gether. Boa con­stric­tors are noc­tur­nal or cre­pus­cu­lar, though they bask in the sun to warm them­selves in cool weather. They pe­ri­od­i­cally shed their skins (more fre­quently in ju­ve­niles than adults). A lu­bri­cat­ing sub­stance is pro­duced under the old skin layer. When this oc­curs, the snake's eye can be seen to cloud up as this sub­stance comes be­tween its eye and the old eye-cov­er­ing. The cloudi­ness af­fects their vi­sion and boas will often be­come in­ac­tive for sev­eral days until the shed­ding has com­pleted and their vi­sion is re­stored. Dur­ing shed­ding, the skin splits over the snout and even­tu­ally peels back from the rest of the body. Boa con­stric­tors are most often ob­served in trees or on the ground near streams and rivers. (Bartlett and Bartlett, 2003; Chiar­aviglio, et al., 2003; Mont­gomery and Rand, 1978; O'Shea, 2007; Stafford, 1986)

• Key Behaviors
• arboreal
• terricolous
• nocturnal
• crepuscular
• sedentary
• solitary
• territorial

Home Range

Boa con­stric­tors de­fend ter­ri­to­ries that change over time. Ter­ri­to­ries may be aban­doned if re­sources or con­di­tions de­cline. (O'Shea, 2007; Stafford, 1986)

Com­mu­ni­ca­tion and Per­cep­tion

Like most snakes, boa con­stric­tors rely on strong vomeronasal senses. Their tongues flick con­tin­u­ously, bring­ing odor mol­e­cules into con­tact with the chemosen­sory (vomeronasal) organ in the top of their mouths. In this man­ner, they con­stantly sense chem­i­cal cues in their en­v­iorn­ment. Boa con­stric­tors have good vi­sion, even into the ul­tra­vi­o­let spec­trum. In ad­di­tion, they can de­tect both vi­bra­tions in the ground and sound vi­bra­tions through the air through their jaw bones. They do not have ex­ter­nal ears. Un­like most boids, boa con­stric­tors lack ther­mosen­sory pits. (Mat­ti­son, 2007; O'Shea, 2007; Sill­man, et al., 2001; Stone and Holtz­man, 1996)

• Communication Channels
• tactile
• chemical

• Perception Channels
• visual
• tactile
• acoustic
• vibrations
• chemical

Food Habits

Boa con­stric­tors are car­niv­o­rous gen­er­al­ists. The main bulk of their diet con­sists of small mam­mals, in­clud­ing bats, and birds. How­ever, they will eat any an­i­mal they can cap­ture and fit in their mouths. Boa con­stric­tors cap­ture prey through am­bush hunt­ing, al­though oc­ca­sion­ally they ac­tively hunt. They can rapidly strike at an an­i­mal that passes by a branch that they are sus­pended from, for ex­am­ple. They are non-ven­omous and prey is dis­patched through con­stric­tion. Boa con­stric­tors wrap their prey in the coils of their body and squeeze until the prey as­phyx­i­ates. This is es­pe­cially ef­fec­tive against mam­mals and birds whose warm-blooded me­tab­o­lism de­mands oxy­gen at a rapid rate. Once dead, the prey is swal­lowed whole. In­ter­est­ingly, if cap­tive boa con­stric­tors are pre­sented with dead prey, they still con­strict the food item be­fore con­sum­ing it. It takes boa con­stric­tors 4 to 6 days to fully di­gest a meal. (Bartlett and Bartlett, 2003; Mat­ti­son, 2007; O'Shea, 2007; Stone and Holtz­man, 1996)

• Primary Diet
• carnivore
  • eats terrestrial vertebrates

• Animal Foods
• birds
• mammals
• amphibians
• reptiles
• eggs

Pre­da­tion

When threat­ened, boa con­stric­tors will bite to de­fend them­selves. Though there are few ref­er­ences to pre­da­tion on boa con­stric­tors in na­ture, they are cer­tainly killed and con­sumed by nu­mer­ous rep­til­ian, avian, and mam­malian preda­tors. Young boas are es­pe­cially vul­ner­a­ble. (O'Shea, 2007; Pough, et al., 2004)

• Anti-predator Adaptations
• cryptic

Ecosys­tem Roles

Boa con­stric­tors are preda­tors on birds and small mam­mals, in­clud­ing bats. They are im­por­tant preda­tors of ro­dents and opos­sums, es­pe­cially, which can be­come pests in some areas and carry human dis­eases. (Mat­ti­son, 2007; O'Shea, 2007; Stone and Holtz­man, 1996)

Eco­nomic Im­por­tance for Hu­mans: Pos­i­tive

Boa con­stric­tors are pop­u­lar in the pet trade. It is easy to ob­tain boa con­stric­tors that have been cap­tive bred for gen­er­a­tions, in­creas­ing their affin­ity for hu­mans. They are rel­a­tively un­de­mand­ing pets, as long as their large adult size and space needs are ac­counted for. Proper lev­els of heat and hu­mid­ity (boas usu­ally need a dry cli­mate, oth­er­wise their scales will de­velop rot) need to be ob­served. Boa con­stric­tors can be fed dead mice and rats and only re­quire food and defe­cate about once a week. Proper care should be ob­served in han­dling them, es­pe­cially the larger va­ri­eties. Boa con­stric­tors, whole or in parts, are also seen in local mar­kets within their range, pre­sum­ably as food or med­i­cine. They are some­times har­vested for the skin trade. In some areas boas con­stric­tors can play a large role in con­trol­ling pop­u­la­tions of pest ro­dents and opos­sums (Didel­phi­dae). Opos­sums in the trop­ics can be car­ri­ers for the human dis­ease leish­ma­ni­a­sis, which is trans­ferred by blood-feed­ing sand flies (Psy­cho­di­dae) that par­a­sitize the opos­sums. Boa con­stric­tor pre­da­tion pres­sure may help to reg­u­late opos­sum pop­u­la­tions and de­crease po­ten­tial trasmis­sion of leish­ma­ni­a­sis to hu­mans. (Bartlett and Bartlett, 2003; Mat­ti­son, 2007; O'Shea, 2007)

• Positive Impacts
• pet trade
• food
• body parts are source of valuable material
• controls pest population

Eco­nomic Im­por­tance for Hu­mans: Neg­a­tive

Lit­tle neg­a­tive im­pact on hu­mans is known. Boa con­stric­tors rarely, if ever, at­tack hu­mans ex­cept in self-de­fense. Hu­mans, even chil­dren, are far out­side the range of prey size taken by boas. Boa con­stric­tor bites are painful bure are un­likely to be dan­ger­ous as long as stan­dard med­ical care is ob­tained. Boa con­stric­tors are not ven­omous. Large cap­tive snakes must al­ways be han­dled with ex­treme care, es­pe­cially when being fed, as a hun­gry snake strikes and con­stricts in a largely au­to­matic se­quence of be­hav­iors. Very large snakes should han­dled and fed only with more than one per­son pre­sent. (Bartlett and Bartlett, 2003; Mat­ti­son, 2007; O'Shea, 2007)

• Negative Impacts
• injures humans
  • bites or stings

Con­ser­va­tion Sta­tus

Over­col­lec­tion for the pet trade and need­less di­rect per­se­cu­tion has had an im­pact on some B. con­stric­tor pop­u­la­tions. Some pop­u­la­tions have been hit harder than other, and var­i­ous wild pop­u­la­tions are now en­dan­gered, par­tic­u­larly those on off­shore is­lands. On the main­land, boa con­stric­tors have been har­vested for their skins, meat and body parts. Fur­ther­more, habi­tat loss and road mor­tal­ity has re­duced pop­u­la­tions. Most boa con­stric­tors are on the CITES Ap­pen­dix 2 list. The sub­species B. c. oc­ci­den­talis is on Ap­pen­dix 1 of CITES. (O'Shea, 2007; Pough, et al., 2004)

• IUCN Red List

  Not Evaluated

• US Federal List

  No special status

• CITES

  Appendix I Appendix II

• State of Michigan List

  No special status

Other Com­ments

As men­tioned above, the species Boa con­stric­tor is di­vided into many sub­species. These sub­species are highly vari­able and over the years the tax­on­omy has changed. Cur­rently there are at least 9 rec­og­nized sub­species: Colom­bian or com­mon boa con­stric­tors (B. c. con­stric­tor), St. Lucia boa con­stric­tors (B. c. orophias), Im­pe­r­ial or Cen­tral Amer­i­can boa con­stric­tors (B.c. im­per­a­tor), Ar­gen­tine boa con­stric­tors (B.c. oc­ci­den­talis), Pe­ru­vian boa con­stric­tors (B.c. or­tonii), Taboga Is­land boa con­stric­tors (B.c. sabo­gae), Bo­li­vian boa con­stric­tors (B.c. amavali), Do­mini­can or clouded boa con­stric­tors (some­times con­sid­ered a full species, B.c. neb­u­losa), and long-tailed boa con­stric­tors (B.c. long­i­cauda). Sub­species that are oc­ca­sion­ally cited, but are not as widely ac­knowl­edged or are often com­bined with a pre­vi­ously listed sub­species are: Mex­i­can boa con­stric­tors (B.c. mex­i­cana), black-bel­lied boa con­stric­tors (B.c. melanogaster), and Tres Marias Is­lands boa con­stric­tors (B.c. sigma). As ap­par­ent by the names, most sub­species are rec­og­nized by their range. In many cases, a boa con­stric­tor of un­known ge­o­graph­i­cal ori­gin may be im­pos­si­ble to as­sign to a sub­species. Ad­di­tion­ally, pet trade breed­ers have cre­ated many new color morphs that are not seen in wild pop­u­la­tions. (An­drade and Abe, 1998; Bartlett and Bartlett, 2003; Mat­ti­son, 2007; O'Shea, 2007; Stafford, 1986)

Con­trib­u­tors

Tanya Dewey (ed­i­tor), An­i­mal Di­ver­sity Web.

Lau­rel Lin­de­mann (au­thor), Michi­gan State Uni­ver­sity, James Hard­ing (ed­i­tor, in­struc­tor), Michi­gan State Uni­ver­sity.

Ref­er­ences

An­drade, D., A. Abe. 1998. Ab­nor­mal­i­ties in a lit­ter of Boa con­stric­tor ama­r­ali. The Snake, 28: 28-32. Ac­cessed De­cem­ber 05, 2008 at http://​ns.​rc.​unesp.​br/​ib/​zoologia/​denis/​boabnormal.​PDF.

Bartlett, R., P. Bartlett. 2003. Red-tailed Boas and Rel­a­tives: Rep­tile Keeper's Guide. Haup­pauge, NY: Bar­ron's Ed­u­ca­tional Se­ries, Inc..

Bertona, M., M. Chiar­aviglio. 2003. Re­pro­duc­tive bi­ol­ogy, mat­ing ag­gre­ga­tions, and sex­ual di­mor­phism of the ar­gen­tine boa con­tric­tor (Boa con­stric­tor oc­ci­den­talis). Jour­nal of Her­petol­ogy, 37(3): 510-516. Ac­cessed De­cem­ber 05, 2008 at http://​www.​bioone.​org.​proxy2.​cl.​msu.​edu/​perlserv/?​request=get-document&​issn=0022-1511&​volume=37&​page=510.

Chiar­aviglio, M., M. Bertona, M. Sironi, S. Lu­cino. 2003. In­trapop­u­la­tion vari­a­tion in life his­tory traits of Boa con­stric­tor oc­ci­den­talis in Ar­gentina. Am­phibia-Rep­tilia, 24/1: 65-74. Ac­cessed No­vem­ber 07, 2008 at http://​apps.​isiknowledge.​com.​ezproxy1.​ats.​msu.​edu/​full_​record.​do?​product=WOS&​search_​mode=GeneralSearch&​qid=1&​SID=1FBABe92cheDGF3aPf6&​page=1&​doc=2.

Mat­ti­son, C. 2007. The New En­cyl­co­pe­dia of Snakes. Prince­ton, New Jer­sey: Prince­ton Uni­ver­sity Press.

Mont­gomery, G., A. Rand. 1978. Move­ments, body-tem­per­a­ture and hunt­ing strat­egy of a boa-con­stric­tor. Copeia, 3: 532-533. Ac­cessed No­vem­ber 07, 2008 at http://​apps.​isiknowledge.​com.​ezproxy1.​ats.​msu.​edu/​full_​record.​do?​product=WOS&​search_​mode=GeneralSearch&​qid=9&​SID=1FBABe92cheDGF3aPf6&​page=1&​doc=1.

O'Shea, M. 2007. Boas and Pythons of the World. Prince­ton, New Jer­sey: Prince­ton Uni­ver­sity Press.

Pough, F., R. An­drews, J. Cadle, M. Crump, A. Sav­itzky, K. Wells. 2004. Her­petol­ogy, third edi­tion. Upper Sad­dle River, NJ: Ben­jamin Cum­mings.

Sill­man, A., J. John­son, E. Loew. 2001. Reti­nal pho­tore­cep­tors and vi­sual pig­ments in Boa con­stric­tor im­per­a­tor. Jour­nal of Ex­per­i­men­tal Zo­ol­ogy, 290(4): 359-365. Ac­cessed De­cem­ber 05, 2008 at http://​apps.​isiknowledge.​com.​proxy2.​cl.​msu.​edu/​full_​record.​do?​product=WOS&​search_​mode=GeneralSearch&​qid=18&​SID=3CdeLbP2E5edFCLGO8P&​page=7&​doc=70.

Stafford, P. 1986. Pythons and Boas. Nep­tune City, New Jer­sey: T.F.H. Pub­li­ca­tions, Inc. Ltd.

Stone, A., D. Holtz­man. 1996. Feed­ing re­sponses in young boa con­stric­tors are me­di­ated by the vomeronasal sys­tem. An­i­mal Be­hav­ior, 52: 949-955. Ac­cessed No­vem­ber 07, 2008 at http://​apps.​isiknowledge.​com.​ezproxy1.​ats.​msu.​edu/​full_​record.​do?​product=WOS&​search_​mode=GeneralSearch&​qid=11&​SID=1FBABe92cheDGF3aPf6&​page=1&​doc=1.