Introduction

Ball pythons (Python regius), also known as royal pythons, are one of the most common pet snakes in the United States. These snakes are native to Central and Western Africa, grow to 0.9–1.8 m (3–6 ft) in length, can live >30 yr in captivity, and have a generally docile disposition that makes them a desirable pet. Ball pythons have experienced an immense growth in popularity recently, with the generation of “designer” ball pythons; the identification of unique mutations has subsequently given rise to various desirable phenotypes, or “morphs,” within the species. A morph is typically a phenotype caused by a single heterozygous mutation, resulting in a characteristic change in appearance. Morphs are most commonly inherited in a co-dominant Mendelian pattern, although multiple exceptions are present. For example, the piebald morph is homozygous recessive, whereas the banana morph is strictly dominant (Fig. 1). At the time of writing, >100 unique ball python morphs (known genetic mutations) have been identified through their changes in phenotypic appearance. In addition, multiple allelic combinations have been selectively produced to increase perceived value. The selective breeding and combinations of these different genotypes have led to the generation of animals that may sell for values >$5,000 (USD). Some of these morphs also have fatal changes associated with them, particularly homozygous animals that are colloquially referred to as “supers,” such as a shaking/ataxic behavior (e.g., spider), infertility (e.g., leopard), or facial malformations (e.g., super black pastel). The underlying genetic sequences and individual genes associated with specific morphs have yet to be elucidated, although some, such as cinnamon and black pastel, are believed to be linked.

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Ball pythons with unique appearances are frequently bred and commonly sold through individual breeders, as well as private and public corporations and pet stores. The sale of ball pythons through pet stores likely remains the most common source of this species overall, with many pet stores now selling various morphs. The online sale of ball pythons has grown greatly in the past 10–15 yr, with many individual breeders and corporations having their own online web sites, in addition to larger conglomerate hobbyist sites. These larger sites include kingsnake.com, faunaclassifieds.com, craigslist.org, petsclassifieds.us, reptileforums.co.uk, worldofballpythons.com, and morphmarket.com, with the latter two sites listing various private breeders. Multiple ball python hobbyist groups are also accessible online through social media such as facebook.com.

There remains a relative dearth of information available on snake reproduction and hormonal control compared with other species, with few studies on reproductive parameters in ball pythons. Although general knowledge of temperature and light sensitivity for breeding purposes is known throughout the reptile hobbyist breeding community, public postings of individual methods for captive reproduction are highly variable. Python and boid breeding and reproductive cycle timing and triggers remain little explored (Whittier and Crews, 1987; Krohmer and Lutterschmidt, 2011), although progesterone concentrations correlate with ball python folliculogenesis and estradiol levels are more variable (Bertocchi et al., 2018). A surplus of literature from the experiences of individual authors is available for other snake species (De Vosjoli, 1994; Purser, 2005; Sutherland, 2005). Specifically, the breeding cycles of the Saharan sand viper (Cerastes vipera) (Sivan et al., 2012), Neotropical Atractus pantostictus (de Resende and Nascimento, 2015), blackbelly garter snake (Thamnophis melanogaster) (Garstka et al., 1983), and the western diamondback rattlesnake (Crotalus atrox) (Taylor et al., 2004) are well documented among reptile species. Yet, the structure and function of snake gonadotropins have not been elucidated (Licht and Pearson, 1969) and may be structurally divergent from other tetrapods (Castoe et al., 2013), and/or snake gonadotropins may have varying degrees of neuroendocrine control over their release (Krohmer and Lutterschmidt, 2011). A lack of understanding of the hypothalamic-pituitary-gonadal axis and its hormonal feedback in snakes is one of the biggest limiting factors in the successful manipulation of their reproductive parameters.

The objective of this cross-sectional study was to assess the current status of hobbyist breeding for ball pythons, to identify similarities and differences in successful breeding schema, to better determine the demographics of ball pythons breeders within the United States, and to determine the need for veterinary intervention and dissemination of husbandry information for breeders. A survey was submitted to professional and amateur breeders through a national breeding convention, a ball python sales site, and through social media outlets. The survey contained questions on demographics, finances, husbandry, diet, temperature, humidity, housing, income, veterinary care, and locality. Among other responses, we hypothesized that there is little-to-no financial incentive to breed ball pythons, that significant gaps exist in snake husbandry compared with recommendations from the ARAV, and that breeding schema result in generally high reproductive success despite differences in substrate, humidity, and temperature.

Materials and Methods

Results

In total, 50 participants provided responses to the survey. The responses are displayed in Tables 1–3. The total number of responses to each question is listed as well, with a maximum response value of n = 50. Respondents that chose to disclose a location (n = 48) were from 25 states: Alabama, Arizona, California, Colorado, Florida, Georgia, Indiana, Illinois, Kentucky, Louisiana, Michigan, Minnesota, Mississippi, Missouri, Nebraska, New York, Ohio, Oklahoma, Pennsylvania, South Carolina, Tennessee, Texas, Virginia, Washington, and Wisconsin. The majority (89.8%) of participants were significantly more likely to consider themselves amateur ball python breeders rather than professionals and own or manage a median of 45 animals (Table 1). The survey respondents purchase a median of 4 animals each year and sell a median of 20 animals per year. Respondents were significantly more likely to sell snakes to private owners (49%) or to both private and corporate owners (49%) than to corporate owners exclusively (Table 1). Participants estimate a median net profit from snake breeding of $30 annually and do not consider a significant portion of their income (median 0%) to be generated from these sales. The calculated median profit per snake is $0. A weak positive correlation was found between the total number of ball pythons owned and net profit (P = 0.002).

Table 1 Ball python (Python regius) breeder demographics. Results are presented as multiple-choice or free response data. The data were non-normally distributed and are presented as the median, range (minimum–maximum [min.–max.]), and 25–75% quartile values (calculated), or as percent response to multiple-choice data with the 95% confidence intervals (CIs). Questions have been re-numbered for the purpose of presentation.

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Table 2 Husbandry and management survey responses for ball python (Python regius). Results are presented as multiple-choice or free response data. The majority of data were non-normally distributed and are presented as the median, range (minimum–maximum [min.–max.]), and 25–75% quartile values (calculated), or as percent response to multiple-choice data, including the 95% binomial confidence intervals (CIs). Questions have been re-numbered for the purpose of presentation.

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Table 3 Ball python (Python regius) breeding schema survey responses. Results are presented as multiple-choice or free response data. The majority of data were non-normally distributed and are presented as the median, range (minimum–maximum [min.–max.]), and 25–75% quartile values (calculated), or as percent response to multiple choice data, including the 95% binomial confidence intervals (CIs). For normally distributed values, the mean, standard deviation (SD), and range are given and are indicated when present. Questions have been re-numbered for the purpose of presentation. Asterisk (*) indicates data not analyzed.

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Survey participants were significantly more likely to house their ball pythons in commercial racks than custom racks or individual terrariums; custom racks were also significantly more likely to be used than individual enclosures by the survey respondents (Table 2). Animals were housed in habitats ranging from 364 to 2,304 in.² of space (median, 561 in.²). For reference, an FB40 rack system (TGR Rack Systems, Vinemont, VT) is 13 in. × 34 in. and has 442 in.² of space. Beyond housing space, respondents were significantly more likely to modify the temperature of the room containing their snakes, with median temperatures of 26.6°C (79.9°F) (Table 2). These snake caretakers were significantly more likely to provide a temperature gradient within the enclosure by using heat tape (79.6%) than other types of heat (Table 2). Most provide a basking temperature of ∼32°C (90°F). There was no difference in the number of respondents who measured humidity vs. those that did not measure humidity, with 50% of respondents being in either category. However, respondents were significantly more likely to not alter humidity at all when breeding their snakes. Participants were significantly less likely to offer their snakes a water access area (bowl) that was large enough for them to enter (No: 80%), a hide or cave (No: 66%), an ultraviolet B (UVB) light source (No: 96%), or access to sunlight (No: 62%). Substrates used vary from aspen/tree shavings (24%), paper products (26%), mulch/husk/fiber (34%), ReptiChip™ (San Antonio, TX) (6%), or other (10%). Based on these responses, ball python breeders were more likely to use mulch\husk\fiber or paper products over ReptiChip. Breeders reported changing substrate, on average, 12 times during the year, equivalent to once per month, with 32% of individuals reporting that they only spot clean enclosures. There was no association between any specific husbandry parameters surveyed and the percentage of eggs reported to hatch (P = 0.208). There was no significant difference in how the prey were offered, with 42% feeding live prey, 36% feeding frozen-thawed prey, and 20% offering a mix of both. There was one exception, with one responder providing fresh killed food (2%). Rats (92%) were significantly more likely to be offered to ball pythons than mice and rats (8%), mice alone, or other food sources. Responders offer food three to four times per month to the adult snakes.

Regarding the health of the snakes, responders were more likely to have visited a veterinarian (71.4%) for a health-related issue with a snake than not. However, respondents were significantly less likely to visit a veterinarian specifically to euthanize a snake (No: 87.8%). There was no difference in whether respondents routinely tested or treated their snakes for ectoparasites (No: 59.2%).

Responses for “How many times in 2 yr will you pair a male/female ball python” were highly variable and were not analyzed (Table 3). In general, rather than give a specific number, many respondents reported that the number of pairings for a male would depend on whether the male was observed to “lock” (copulate) with the female, or whether the female would become gravid after pairing. Similarly, female copulation times were reported to vary if females were observed to become gravid, although four responders (8%) independently reported that females were limited to one clutch per year. Most pairings were set up year-round (33%) or in the fall during October (31%) and November (27.1%). There was no difference in the likelihood of these timed pairings; however, respondents were more likely to pair snakes year-round, in October, or in November compared with July or December. Respondents generally did not alter photoperiod during the year (No: 82%) or the breeding season (No: 89.6%). They were also significantly less likely to alter the environmental temperature (No: 66%) during the breeding season. Snakes were most commonly paired in their normal housing racks (81.6%) for an average of 3.3 days. The median minimum weight of females required for breeding was 1,500 g, whereas the average minimum weight for a male was 596 g. Before pairing, most respondents (Yes: 93.5%) do not prescreen females with ultrasound for follicle presence.

According to respondents, females were reported to lay eggs 60 days after breeding. All participants reported that eggs were separated from the female once laid. Eggs were significantly more likely to be incubated in custom incubators (70%) than commercial (26%) or small reptile incubators (4%). Eggs were reportedly maintained on vermiculite (42.9%); other substrates included perlite (24.5%), Hatchrite^TM (Rodeo, NM) (10.2%), combination substrate (14.3%), no substrate (4.1%), or another substrate (4.1%). Eggs were incubated at 31.7°C (89°F) and 95% humidity. There was no difference in whether respondents candled (57.8%) or did not candle the ball python eggs to determine whether they were fertile, or assist with pipping eggs or hatchlings by removing opening part of the shell (Yes: 55.1%). Participants reported a 99% successful hatching rate of incubated eggs. Once hatched, breeders were significantly more likely to sex the hatchlings via hemipenal eversion (74%) than other sexing methods. There were no associations between reported hatch rate for fertilized eggs with type of substrate (P = 0.356), temperature (P = 0.097), or humidity (P = 0.903). Lastly, approximately half (Yes: 48%) of respondents reported that they would not be interested in products that circumvent any changes to feeding, light cycle, or temperature for ball python breeding.

Discussion

Although full data are not available, the most recent data suggest that ∼1,358,000 snakes are kept in captivity across the private sectors in the United States and the United Kingdom and in zoological intuitions within the Association of Zoos and Aquariums (Pasmans et al., 2017). Ball pythons are now a major interest to reptile or herpetological enthusiasts and hobbyists and will likely continue to expand in popularity. Despite being presented to a large population of ball python enthusiasts, the total number of responses to the survey presented suggests that relatively few hobbyists actively engage in breeding. Consequently, many of the captive-bred ball pythons in the United States are produced by a relatively small number of private breeders that vend to both private individuals and corporations. Despite the growing market, the results of this survey show that most snake breeders make little-to-no substantial income from the snakes they breed and instead keep snakes only as a hobby. Although this study is limited in scope, the data show that only a small percentage of individuals can or will capitalize on the reptile market and profit from the production of ball pythons and that this is weakly correlated to having a large number of snakes. In this study, only 5 (11%) of 45 respondents made ≥$10,000 in profit per year from snake breeding. These individuals reportedly manage/own a median of 400 snakes (range: 31–700) and sell a median of 100 snakes per year (range: 40–500).

The current husbandry recommendations by the ARAV for ball pythons include an enclosure that is “relatively large,” ambient temperature of 27–29°C (80–85°F) with a basking area of 32–33°C (90–92°F), a room ambient temperature that should not fall under 23.9°C (75°F), access to hide boxes, a water bowl, and an area with high relative humidity of 60–80%. The substrate of choice is newspaper, paper towels, indoor-outdoor carpet, or synthetic grass such as Astroturf® (ARAV, 2016). Recommendations are displayed in Table 4. Respondents to this survey maintained temperatures that were, in general, similar to the ARAV recommendations, although many chose to use substrates other than paper products or synthetic carpeting. Nearly all respondents in this survey keep ball pythons in a rack system rather than an individual terrarium; no specific recommendation has been made between the two, as each may provide adequate space and hiding locations to reduce stress. Most husbandry guides suggest that ball pythons are housed based on age/size, where hatchlings require at least a 10-gal tank (25 × 50 cm [10 in. × 20 in.]), young adults a 20-gal tank (31 × 60 cm [12 in. × 24 in.]), and large adults need a 30-gal tank (31 × 90 cm [12 in. × 36 in.]) (ARAV, 2016). The minimum length of the tank should be at least two thirds of the snake's body length; thus, in a snake that may reach 1.8 m (72 in.) in length, the minimum length of the tank should be 1.2 m (48 in.). A tank or rack that is 48 in. × 24 in. has a footprint of 1,152 in.², or 8 ft. Median enclosure size reported for this survey was 561 in.², whereas enclosures ranged from 364 to 2,304 in.². This is equivalent to ∼3.9 ft². Most rack systems range in diameter from 0.3 to 0.5 m (12 to 20 in.) in diameter, which leads to the largest total length possible being ∼1 m (∼40 in.). These types of enclosures may limit the ability of larger ball pythons to exhibit their normal behaviors, such as extending their body out fully or traveling more than one body length at a time for exercise purposes to maintain muscular integrity. Of the respondents, few reportedly kept these animals in enclosures that were large enough to allow full extension of their body based on the maximum length of the enclosure. Volume of the surveyed systems was not considered as height generally remains too low for arboreal locomotion in commercial rack systems, although there is evidence that ball pythons exhibit arboreal travel and feeding behavior (Luiselli and Angelici, 1998). Additional physical enrichment or increased housing space may provide a measurable health benefit in this species.

Table 4 Recommendations for captive ball python (Python regius) husbandry. Data presented are derived from the 2016 ARAV Ball Python Companion Reptile Care Series sheet, published through the North American Veterinary Community. The husbandry data presented here are for general care of ball pythons and do not account for changes during breeding such as snake introductions, nesting boxes, or feeding schedule/volume.

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Few respondents (34%) provided a hide or similar structure for their animals. Access to a hide may decrease stress in snakes in captivity, and this represents one possible area for improvement in housing, as even household objects such as shipping boxes may be repurposed for hides (Mitchell, 2004). Similarly, few respondents (20%) provide a volume of water large enough for snakes to fully submerge themselves, suggesting that this is not something they see as important to breeding this species. This behavior is rarely observed in captivity, but it may occur in response to dehydration to absorb water through the cloaca and colon, as has been documented during medical rehydration (Boyer and Scott, 2019). It is also a common method used by snakes to self-manage ectoparasite infestations (e.g., snake mite, Ophionyssus natricis).

Rats were the predominant food being offered to the ball pythons. Rats should be considered a complete diet, although how the animals are raised can lead to health conditions for the snake (Mitchell, 2004). A majority of respondents also reported the feeding of live prey. This methodology is generally discouraged because it is considered inhumane to the prey animal and can pose a health threat to the snake (Mitchell, 2004). Rodents offered to snakes have been found to injure the snake if not eaten. Some ball python owners will suggest that a subset of ball pythons will not feed on frozen-thawed or fresh-killed rodents; however, the authors have found that with patience and different trials by using various scents (e.g., gerbil, lizard) that these snakes will feed on prekilled foods. In addition, care should be given to feeding frequency in captive snakes, with ARAV guidelines suggesting feeding every 7–10 days for the first 2–3 yr of age and approximately every 2 wk thereafter. Obesity and increased body conditioning/fat content remain an ongoing issue in many captive snakes.

In this survey, 48 (96%) of 50 respondents did not expose their ball pythons directly to UVB light. This is consistent with the peer reviewed literature that found ball pythons did not significantly increase their blood vitamin D concentrations after exposure to UVB light, unlike corn snakes (Pantherophis guttatus) and Burmese pythons (Python bivittatus) (Acierno et al., 2008; Hedley and Eatwell, 2013; Bos et al., 2018). It has been hypothesized that due to their life-history strategy, and being primarily crepuscular, they do not require UVB lighting. However, these data are extrapolated from a single study, and in other crepuscular species, such as the leopard gecko (Eublepharis macularius), a physiological response to UVB exposure has been found (Gould et al., 2017). Additional studies in ball pythons may be performed to fully elucidate the need for UV light and confirm whether calcium homeostasis in this species is fully or partially independent of UVB exposure. Although a fair percentage (38%) of respondents reported that their ball pythons had access to sunlight through a window, it should be noted that UVB light is defracted by glass to a nearly negligible level and that this light may affect photoperiod cycling but would likely have no impact on vitamin D homeostasis.

Although ball pythons have been kept and can reproduce successfully in captivity under these reported conditions, this is not necessarily a good indicator of welfare. In addition to regular reproduction, regular feeding behavior, lack of enrichment, and small enclosure size have been associated with captivity-related stress, which allows for a re-direction of resources to basic biological functions (Warwick et al., 2019). No regulations exist within the private sector or pet trade establishing minimum husbandry requirements for reptiles within the United States and Europe. Considerable welfare problems still occur in captive reptiles and amphibians with all types of keepers, although these issues are often highlighted in novice keepers (Pasmans et al., 2017). Perception of ball python husbandry practices have been standardized to an accepted set of commercially produced housing systems rather than to a set of minimal welfare care and considerations. Novice or hobby breeders may pursue husbandry approaches that are based on products commonly provided by producers rather than taking into consideration the welfare concerns of each individual animal. The minimum husbandry requirements as outlined by the ARAV should be considered for all ball pythons and altered over time as the animals grow and require new enclosures (Table 4).

In this study, we did not observe any specific breeding requirements that enhanced breeding efforts by the respondents. However, these data may be biased because many of the respondents manage their ball pythons by using similar husbandry methods. Large-scale scientific studies using small modifications to temperature, light, humidity, feeding, and a combination thereof are necessary for specific recommendations of the highest quality. Of interest are factors that mimic the conditions from where ball pythons originate. For example, mimicking the ambient lighting and humidity of west central Africa during the dry/wet seasons may induce or improve induction of mating behavior. It may be useful to enroll large-scale breeders in such studies. In addition to animals produced, hormones and ultrasonography can serve as important indicators for total reproductive success or viability. Only 6.5% of respondents reported that they actively ultrasound (sonogram) their females to observe follicular development. In ball pythons, when follicular size of the largest follicle reaches 25 mm, the number of developing follicles appears to be predictive of clutch size (Nielsen et al., 2016). Bertocchi et al. (2018) used fecal steroid metabolite measurements in correlation with ovarian ultrasound to correlate hormonal levels in reproductively cycling pythons. Ovarian ultrasound may be an option for breeders in the future, especially as inexpensive handheld and phone-linked ultrasound probes become available.

Interestingly, none of the respondents used maternal incubation, although it is a known method of successful incubation in pythons. This may be attributed to the production mentality of the hobbyist and the belief that it adds excessive stress to the female. Removal of the eggs from a coiled female allows the female to begin eating sooner, which would allow faster weight gain to reproduce. At present, there is no consensus on whether maternal incubation has any influence on offspring viability. Although maternal care has been documented in some snake species, it is unknown at this time whether ball pythons exhibit posthatching maternal care (the amount of maternal investment in wild populations is likely minimal). Hobbyist breeders appear to incubate their eggs in custom incubators a majority of the time, with ∼30% using commercially produced incubators. Respondents used different types of substrates for incubating eggs, although vermiculite and perlite were most commonly used. A small minority (4.1%) of respondents did not use any substrate for incubation. Further scientific study on the types of substrate used for incubation in this species may elucidate the role of substrate on potential differences in weight, age, or other health parameters at the time of hatching.

Ball pythons have been demonstrated to have chromosome-based sex determination (Gamble et al., 2017), and many breeders incubate their eggs at the same temperatures (32°C [89°F], median in this study). A nonsignificant majority of these individuals take a hands-on approach to hatchling management by candling the eggs to assess viability. Performing this technique shows that the respondents are being proactive in evaluating the reproductive success of their snakes. It was also interesting to note that a nonsignificant majority of respondents assist with hatching. Whether this assistance in captivity is truly needed or not should be investigated further. If assistance is required, evaluating why this is necessary (e.g., maternal shortcoming, embryo shortcoming) should be pursued. Although the majority of respondents performed these functions, the overall reported hatching success rate was 99%. With such a high hatching success rate, one might question the value of these techniques if the same results can be gained with less effort. Of course, there is the potential for reporting bias in a survey; thus, to determine the true value of candling or assisting with hatching, a well-designed experimental study should be done.

In our study, we observed that a significant majority of individuals (71.4%) reported using veterinary care for their ball python(s). However, there was also a significant minority (12.2%) of respondents that would take a ball python to a veterinarian to be euthanized. Multiple reasons exist for a limited number of individuals pursuing humane euthanasia, including unexpected deaths in collections, limited resources (e.g., not wanting to pay for euthanasia), longer life expectancy of ball pythons than most small animals, or inhumane alternatives (including freezing without sedation, decapitation). As previously stated, a majority of individuals will use veterinarians for the care of ball pythons; therefore, a separate explanation must exist for low percentage reporting euthanasia with a veterinarian. A shortfall of this study was that the owner's use of the veterinarian was not described, although this was not the direct objective of this study. Further evaluation of how ball python owners/breeders use veterinarians may be useful to determine trends and opinions of veterinarians within the herpetological community. This may allow veterinarians to market directly toward and target prospective clients. In addition, a further understanding of client expectations from veterinarians may allow veterinarians to appeal to a broader and larger audience within the herpetological community.

There were several limitations associated with this study, including the limited number of responses; the large number of survey questions; the need for follow-up with more focused questions; a lack of normally distributed data and consequential lack of more robust statistical analyses; potential bias in interviewing; bias in web site and conference attendance and locality; recall bias; and self-reporting bias. These limitations may result in the data being skewed or over-represented to those breeders who frequent hobbyist web sites and who have the resources to attend and purchase/sell at a breeder conference, or bias the data to show an increased or decreased income, number of animals owned, or a conformity to previously reported recommended husbandry parameters rather than those used.

Conclusions

Overall, this survey collected responses from individual ball python breeders that suggest that ball pythons will reproduce in captivity despite a variety of housing conditions. There was no statistical difference in the reported breeding success despite a wide variety of breeding schema, including time of year of pairing and differences in lighting, temperature, or humidity. Most schema used are similar to published veterinarian-recommended ball python housing conditions, although the addition of a hide, large water bowl, and an enclosure up to 1.2 m (48 in.) in length should be considered. The results of this survey also suggest that no substantial income is derived from the breeding and selling ball pythons in the United States, which is a key point that should be conveyed to new members of the hobby before making any significant investments of time and money needed to maintain this species. Lastly, this survey indicates that many ball python breeders have never had an animal euthanized through a veterinarian, which presents an area for further study to potentially improve the quality of life for this species at the end of life, whether through medical advancements or owner education of signs of distress. Potential limitations of this study are the small sample size, lack of self-identifying “professional” breeders, and a shortage of information on the total number of pairings to achieve fertilization and clutch size and their relationship to the above parameters. These results provide an initial snapshot of the private ball python breeder sector in the United States and may be used for guiding husbandry recommendations, emphases for owner education, and additional reproductive research in the future.