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Captive Husbandry and Breeding of Boa Constrictors, Boa constrictor spp Robert Nathan, DVM Barberton Veterinary Clinic, 4873 Richland Avenue, Norton, OH 44203 USA

Abstract: Since boa constrictors, Boa constrictor spp, have been and continue to be a popular part of herpeto- culture it is important for reptile veterinarians to be familiar with their captive husbandry. Appropriate care is outlined in this paper. Breeding techniques are also suggested for those who are interested in captive propagation. Downloaded from http://meridian.allenpress.com/jhms/article-pdf/11/2/30/2207126/1529-9651_11_2_30.pdf by guest on 29 September 2021

Key W ords: Boa constrictor, Boa constrictor spp, captive husbandry, inclusion body disease.

INTRODUCTION Taxonomists do not all agree on the classification of boa constrictors. They belong to the family Boidae and the sub­ Boa constrictors have been a staple in the pet reptile trade family Boinae. Depending upon the taxonomist, there are for many years. Their popularity continues today, especially between six and ten subspecies recognized. Recently Kluge with the continued development of several new color and pat­ (1991) recommended changing the generic names of the tern mutations. Captive boas generally have rather placid Madagascar boas, Acrantophis and Sanzinia, to Boa spp. It demeanors. They can attain a relatively large size with some remains to be seen if the scientific community will accept specimens reaching approximately four meters, however most these recommendations. All currently recognized boa con­ are smaller. strictors are listed by the Convention on the International Trade Boa constrictors have an extensive range throughout the in Endangered Species of Wild Fauna and Flora (CITES) as neotropics. Boas occur naturally from about 28° north latitude appendix II, which means special permits are required between in Mexico to roughly 38° south latitude in Argentina (Barker the importing and exporting countries. One subspecies, the and Barker, 1994). Boas exhibit a wide variation in size, Argentine boa constrictor, Boa constrictor occidentalis, is list­ color, and pattern. The boa that is most common in the pet ed as endangered (appendix I). This prohibits export from trade is referred to by herpetoculturists as the Columbian boa Argentina and Paraguay, and also requires special permits to constrictor, Boa constrictor imperator. Most are collected allow import/export of captive-bred specimens. from the Magdalena River Valley and shipped to the United States from Baranquilla, Columbia (Carlzen,1990). HUSBANDRY

It is best to house each boa constrictor individually, except during breeding attempts, de Vosjoli, et al (1998) recommend that juvenile boas be housed in enclosures at least 61 cm (24 in) long and 38 to 61 cm (15 to 24 in) high. Adult boas should be housed in enclosures at least 1.8 m (six feet) long, 61 cm (24 in) wide, and at least 61 cm (24 in) high. Larger cages provide better opportunities for establishing a proper thermal gradient. There are numerous substrates currently available. This author prefers using newspaper or butcher paper. It is inex­ pensive and easy to replace when soiled. Each also has the added benefit of allowing direct visualization of the feces and urates. Several other substrates are commonly used by her­ petoculturists and include artificial turf, aspen or pine shavings (not cedar), and various mulches. Artificial turf can hide wetness. Ideally, a second set of turf should be available to allow cleaning and drying of the one not in use. Dilute bleach water (1:30) is useful to disinfect enclosures and turf During a river cruise in Costa Rica we stopped for lunch at a provided that all organic matter has been washed away prior compound with a series of huts. We expressed a desire to see to application. Shavings and mulches need spot cleaning as native snakes, which caused one of the residents to comment that they become soiled and periodic replacing. In addition these he had recently found a boa in the jungle and brought it home to products can be irritating to the oral mucosa if inadvertently place under his hut to catch rats. He volunteered to see if it was picked up during food prehension. still there and found it with ease. The snake had a huge ingested Providing a proper thermal gradient is critical to the well meal in its stomach. The boa was nothing like the captive-born being of the snake. The preferred optimal temperature zone pets we see in practice, but was wild and struck viciously at any during the day is between 27 - 29°C (80 - 85°F), with a basking movement. Photo courtesy of Steve Barten, DVM 30 Journal of Herpetological Medicine and Surgery Volume 11, No. 2,2001 spot up to 35°C (95°F). Night time lows can be between 21 - to stabilize the cloaca. The thumb of the opposite hand is 27°C (70 - 80°F). A thermal gradient can be achieved by placed about two centimeters caudal to the vent. Apply pres­ using any of several commercially available products. The sure with the thumb as you gently roll it toward the cloaca. author prefers using ventrally mounted fiberglass heat mats In male boas, the hemipenis should be everted. If either of that are thermostatically controlled (Kane Manufacturing the above techniques are not done properly there is the Co., Des Moines, IA). These mats come in various sizes and potential for injury to the snake. should be no larger than 25 to 30% of the surface area of the Sexual maturity should occur between three to five years cage. Breeders also frequently use Flexwatt or plumbing of age if appropriately fed and maintained. Males may be “heat tape,” however both require some wiring and should sexually mature at a younger age and a significantly smaller be assembled with a rheostat. Minimum-maximum ther­ size. It is important for the snakes to be well fed and healthy mometers are useful to assess temperature variation. prior to any breeding attempts. Well fed snakes have ade­ Humidity is an often overlooked aspect of captive hus­ quate body reserves for breeding, but should not be obese. bandry for boa constrictors. However, it is important for Males may be somewhat leaner than females. In fact, many proper ecdysis and optimal respiratory function. Relative breeders feel that lean, but adequately fed, males make bet­

humidity should be at least 50 to 70%. During ecdysis, the ter breeders than overweight specimens. Downloaded from http://meridian.allenpress.com/jhms/article-pdf/11/2/30/2207126/1529-9651_11_2_30.pdf by guest on 29 September 2021 humidity should be higher. Nevertheless, it is important that There are different techniques used by breeders to encour­ the snake is not constantly laying on a wet substrate. Hide age proper vitellogenesis and spermatogenesis. Breeders of boxes that contain moistened sphagnum moss are an excel­ boa constrictors generally begin preparing the snakes for lent way to provide an area of locally increased humidity. cycling in either November or December. The snakes should Feeding boa constrictors is generally straightforward. It is not be fed for at least two weeks prior to the cooling period. important to select appropriate size prey for the snake. The The temperature is gradually decreased to 21 - 24°C (70 - prey item should not be any larger than the girth of the snake 75 °F). Some breeders also decrease the available light to the at midbody. Juvenile boas should be fed an appropriate size snakes. Others, keep the snakes during this period at their rodent(s) weekly. As boas reach adulthood, it is appropriate preferred daytime high temperatures, but drop the nighttime to decrease the feeding interval to every ten to fourteen days. low to 21 - 24°C (70 - 75°F). It is possible to utilize a combi­ Adult boa constrictors can be maintained on either adult rats nation of these two techniques (Fogel, 1997). The boas are or appropriately sized rabbits. usually kept under these conditions for four to eight weeks. It is recommended to feed either freshly killed or frozen It is important to monitor them during this period for evi­ and thawed (warmed to body temperature) prey. The prey dence of any respiratory disease. Consistently keeping boas items should be humanely euthanatized using acceptable cool without the ability to bask within their preferred tem­ methods. This practice is both safer for the reptile and more perature range for at least part of the day is likely to result in humane for the prey. Prey has a finite fife in the freezer and respiratory infection and is therefore not recommended by should be used within six months of freezing. Frozen prey this author. Ronne (1998) suggests that boas may cycle as may lose some water-soluble vitamins during the result of the decreasing length of day light available to them freeze/thaw cycle. in the Northern Hemisphere during the autumn and by reducing their food intake. REPRODUCTION Boa constrictors that have been cooled for breeding should be gradually warmed to their preferred optimal tem­ Boa constrictor species occupy a vast natural range and as perature zone. During this time the male boas are usually a result the various subspecies are subjected to different introduced into the female’s cage. This is done since males environmental factors. Hence, the following recommenda­ in the wild actively seek out receptive females during the tions are for boa constrictors in general, not for each breeding season. Some breeders may start the male introduc­ subspecies. However, these generalizations should be useful tion either at the beginning or at sometime during the for most. The reader is encouraged to learn as much as pos­ cycling period. If no courting attempts have been made after sible about the natural history of the subspecies being kept. two to three days the male should be removed. The males Sexing boas can easily be accomplished by probing, will actively seek out a receptive female. If one is found, the which is the author’s method of choice. An appropriate sized male will crawl on top of her and he may try to align his blunt metal probe is inserted into both sides of the cloaca in cloaca with hers while digging his cloacal spurs into her a caudal direction. The probe will pass two to four subcaudal sides. The male is then reintroduced to the female at two to scales in a female snake and seven to eight or more subcau­ three week intervals. The female can be fed during this time. dal scales in a male. Probing should always be done gently. Males usually refuse food during this period. Some breeders Male boids often have larger cloacal spurs and longer, thick­ recommend using multiple males to increase competition. er tails than females. Courtship will last three to eight weeks before the An alternative sexing technique referred to as “popping” characteristic preovulation swelling occurs in female snakes. has been used by some. It causes manual eversion of the The swelling occurs about two-thirds down the length of the hemipenis in newborn snakes. This technique works only in body. This swelling corresponds to normal vitellogenesis. newborn boas since the retractor muscle of the hemipenis is Ovulation often occurs two to three weeks later. In some cases, immature. The snake is positioned to allow the caudal part ovulation may occur up to three months later (Ronne, 1998). of the body to sit in a ventral/dorsal position. The thumb of Copulation should occur during the process of follicular one hand is placed just cranial to the vent. The index finger development. The male will breed the female multiple times. of that same hand is placed on the dorsal surface of the body Breeding attempts usually cease prior to ovulation. During

Volume 11, No. 2,2001 Journal of Herpetological Medicine and Surgery 31 ovulation female snakes may again swell in the same area as recurring cases, a thorough medical work up is indicated. before. Both ovaries do not necessarily ovulate simultaneous­ Complete blood count, plasma chemistries, colonic/gastric ly. Females usually begin-a shedding cycle within a week of washes, fecal analysis, contrast radiographs, and endoscopy ovulation. The female will remain a darker than normal color may be necessary for proper diagnosis. during her gestation. Boa constrictors seen in clinical practice commonly are It is important to provide the gravid female with a suffi­ infested with the snake mite, Ophionyssus natricis. The mites cient thermal gradient. In general, gravid females will seek may cause significant disease in affected snakes. Anemia, out higher temperatures than non-gravid females. Monitoring septicemia (often Aeromonas hydrophila), and dermatitis can the behavior of the female is important. If she is incessantly occur. Mites may also be a vector of inclusion body disease of i basking, it is prudent to provide her with a higher temperature. boids. A number of treatments for mite infestation have been However, she may be too warm if she is consistently avoiding recommended by different authors and are beyond the scope; the basking area. Birth defects may occur if the female is not of this paper. Regardless of the treatment method employed, exposed to a proper thermal environment. Some females may excellent husbandry with debulking mites and mite eggs in the lay on their sides, especially during the latter stages of gesta­ environment is necessary for mite eradication.

tion. Females usually continue to feed throughout gestation, Inclusion body disease (IBD) is one of the most significantDownloaded from http://meridian.allenpress.com/jhms/article-pdf/11/2/30/2207126/1529-9651_11_2_30.pdf by guest on 29 September 2021 but often not as aggressively. It may be prudent to feed the diseases affecting boa constrictors today. Inclusion body dis-! gravid female with smaller than normal prey items. ease is thought to be caused by a retrovirus that is associated Gravid females become restless up to one week prior to par­ with cytoplasmic inclusions in epithelial tissues. Affected turition, which occurs approximately four months after snakes may exhibit signs of central nervous system disease, ovulation. Litter size can range from six to 65 depending upon refractory pneumonia, regurgitation, and neoplasia. Currently, the size and subspecies, with 25 being typical (Ronne, 1998, no serologic test is available for screening snakes. Jacobson Ross and Marzec, 1990). Healthy females should aggressively (1999) recommends biopsies of the esophageal tonsils, gastric begin to feed within a couple of days after parturition. mucosa, and liver, as well as complete blood counts for ante- Neonate boas should be placed on moistened paper towels mortem diagnosis. Unfortunately, a negative biopsy does not until their first shed, which usually occurs within tens days of definitively rule out IBD. Currently, no therapy is available birth. Otherwise, they may be housed as per juvenile boas. for affected snakes and euthanasia is recommended to prevent The neonates usually will start to feed after their first shed. transmission to other snakes. A complete review of diseases affecting boas is not possi­ COMMON MEDICAL PROBLEMS ble here. Good husbandry plays a significant role in disease prevention. Appropriate quarantine is an important part of Many of the medical problems seen with captive boas are a good husbandry. Boa constrictors should be quarantined for at direct result of suboptimal husbandry. In most instances, poor least three to six months before being" added to an established husbandry takes its toll slowly over time. Ultimately, these collection -the longer the quarantine the better. immunocompromised animals become clinically ill. Respiratory tract disease is one of the most common REFERENCES sequella to providing an inadequate thermal environment. Boas with respiratory tract disease may have audibly abnor­ Barker D, Barker T. 1994. Boas in the spotlight. The mal breath sounds. These snakes will often open mouth Vivarium, 6 (2):38-41. breathe and rest with their head held vertically. A copious vis­ Carlzen G.1990. Captive propagation and husbandry of the cous discharge may be noted both in the glottis and oral Anerthyristic Boa, Boa c. constrictor, with a brief overview of the cavity. These snakes should be warmed to the higher end of species. Proc IHS on Captive Propagation and Husbandry, 13-24. their preferred optimal temperature zone. It is also important DeNardo D, Mader D.1996. Reproductive biology. In Mader to properly humidify the environment to decrease the viscosi­ D (ed): Reptile Medicine and Surgery. WB Saunders Co, ty of the respiratory secretions. As part of a thorough medical Philadelphia, PA:212-224. work up, either a tracheal or lung wash should be performed deVosjoli P, Klingenberg R, Ronne J. 1998. The Boa Constrictor for cytology and culture and sensitivity. Chemotherapeutics Manual. Advanced Vivarium Systems, Inc., Lakeside, CA. should be instituted based on cytology and culture results. Fogel D. 1997. Captive Husbandry and Propagation of the Gravidity is physically demanding and as a result pregnant Boa Constrictors and Related Boas. Krieger Publishing Co., females may present with respiratory infections. Antibiotics Malabar, FL. have not been reported to be teratogenic or abortifacient in Jacobson E. 1999. Roundtable on inclusion body disease. Bull snakes thus far. DeNardo (1996) reported using amikacin and ARAV, 9(2): 18-25. trimethoprim sulphate in gravid females without any unto­ Kluge A. 1991. Boine phylogeny and research cycles. ward effects. Similarly, Ross (1990) lists ampicillin, Miscellaneous Pub, Museum of Zoology, University of tetracycline, choramphenicol, gentamicin, amikacin, tylosin, Michigan, 178:1-58. and metronidazole as being used without negative effects. Ronne J. 1998. Breeding Columbian Boa constrictors. In de Vomition/regurgitation is a frequent problem for captive Vosjoli (ed): The Boa Constrictor Manual. Advanced Vivarium boa constrictors. Common husbandry problems that result in Systems Inc., Lakeside CA. vomiting/regurgitation are a lack of a proper thermal environ­ Ross R, Marzec G. 1990. The Reproductive Husbandry of ment, excessive feeding, and postprandial handling. Pythons and Boas. The Ins Herp Res, Stanford, CA:209-213. Neoplasia, foreign bodies, bacterial, viral, and parasitic infec­ tions may all cause vomiting/regurgitation. In chronic or

Journal of Herpetological Medicine and Surgery Volume 11, No. 2,2001