The Rainbow Boas are amongst the most beautiful snakes in the world, iridescent to the extreme and intense in colouring. Probably the best known is the Brazilian form, but two other "races" are commonly kept in captivity, the Columbian type and the Argentinean type.
We will look in depth at the climatic and environmental factors that affect their lives, moving towards more appropriate husbandry and homing practices.

There are up to ten different subspecies of cenchria, each subtly different. However, without scale counting, many of them are hard to differentiate and, for the purpose of the keeper, it is sufficient to consider them in only three, what we will call, "races".

They have a range that encompasses much of South America, from Trinidad and Columbia in the north down to the massive Argentina in the south. South America has a length of nearly four thousand miles, stretching from 10 degrees north to 53 degrees south, and width of approximately two and a half thousand miles across. Covering much of that land mass cenchria have become among the most successful of the family Boidae. With such a range the habitats and climes vary greatly but, as you will se,e there are many similarities in terms of care between the three types, if not appearance.

Columbian race
The northernmost of the types is of the subspecies maurus. It is darkest in appearance and the adults exhibit a much-reduced pattern. Neonates are born looking similar, if a little less vibrant, to the Brazilian type, but their pattern fades over the first months.
It is moderate in size, commonly between five and seven feet, and heavier bodied than the other two, though this is in part an illusion due to their small, burrowing type head.

Brazilian race
The most iridescent and colourful and also the largest make these the best known. They can reach eight feet in length with an approximatlye uniform moderate girth.
The Peruvian subspecies, gaigei, is somewhat larger and darker than the true Brazilian, cenchria, but is not common in captivity. It can be distinguished by larger scales that give a mid body scale count of only 41-45 as opposed to 47-51.
The second very similar subspecies is the Marajo Island, barbouri, from the estuarine island of the Amazon. This one is slightly smaller and also darker. Both subspecies have thicker darker markings than the true Brazilians.

Argentinean race
By far the smallest, around five feet, and lightest in colouring these are from the furthest south and, once established, are generally the easiest to care for.

Straddling the equator, Brazil has typical anticyclonic weather. The Inter Tropical Convergence Zone (ITC), is a loop of low pressure encircling the earth near the equator, where air from north and south converges and rises into the atmosphere. It's a few hundred miles wide and caused for the most part by the heating of the earth by the sun. Along the ITCZ the convergent air rises, causing the saturated air to condense out, resulting in significant and consistent monsoon-like rainfall.
The angle of inclination between the earth's axis and plane of rotation is 23.5 degrees; it is the cause of the movement of the sun north in summer and south in winter. Lagging only shortly behind is the ITCZ and its rainfall. With the ITCZ's thickness, and apparent double pass over, the climate at the equator can be considered as "rainy" all year round, so that snakes from a thin band either side come from a near stable climate.
Further north and south there is a more defined wet and dry season, only evened out a little by the sponge-like properties of the rain forests.
Further south in Argentina there is no wet and dry season but, instead, more of a winter as we know it. This is reaching the very extremities of cenchria's range and, although they can cope with lower temperatures than many boids, they cannot cope with a winter, as tolerated by the North American colourbrids.

Pattern, iridescence and build

A defence mechanism of the rainbow boa is to confuse predators as to which end is their head (not to the extent of the sub families Erycinae - Sand, Rubber and Rosy boas - or Calabarinae - the Calabar python). Linear thickness, small heads and patterning that make it very hard to determine which end is which. Furthermor,e they will often burry their head among coils to protect it.
Dorsal ocelli (spots) act to break up their outline among the leaf litter (its effectiveness can be seen if you look at a coiled up adult, it can be difficult to tell how many animals there are and where the coils begin and end).
Living next to swamps and rivers in already wet rainforest,s the boa's shiny appearance, which is the cause of their iridescence, gives them the correct texture, blending them with the moistness of the ground. Notably, the dryer the range the less the iridescence, with the Brazilians having the most, then the Columbians and finally the Argentineans.
The cause of the staggering rainbow effect is a clear epidermal (skin) layer. White light, consisting of all the colours of the spectrum, enters this layer. When these light rays enter at an angle, other than 90 degrees, refraction takes place. Each wavelength (colour) bends to a differing degree - blue the least and red the most - so that when they reflect and exit the white light has been split into its constituent colours.
Rainbow boas are aptly named. The process that occurs in their skin is exactly that which occurs in the water droplets that are the cause of rainbows. To view the iridescence in all its brilliance you need good quality light, constituent of all the colours. Natural spectrum light from a good quality reptile lamp is fine, but nothing is a substitute for a good summers day. Lighting from above gives the best angle for production of the iridescence, so I always view specimens at midday. On the right day with the right specimen the results can be breath taking.
For the photographers out there it may be surprising, but digital cameras are apt at picking up the rainbow, and these fantastic snakes, being docile and pretty, make fabulous studies.

Brazilians have the most specific requirements of the three races we have defined. Coming from nearest the equator where there is the thickest forest and highest rainfall, they need the greatest humidity. Humidity can be tricky to provide in captivity, it encourages the growth of bacteria and propagation of odours and, at the same time limits the materials we can use for the construction of vivaria..
A plastic sized shoebox seems appropriate for hatchlings, and is easy to keep sterile at the 70% or so humidity necessary to prevent shedding difficulties. A hide, perhaps containing damp moss, can aid with shedding and reduce stress.
Adults are less sensitive to humidity, and shedding problems less of a threat. With this in mind I tend to only keep them at 55-60% humidity throughout their shedding cycle. I do, however, provide them with a large shallow water dish and box containing damp sphagnum moss - as with hatchlings. Rainbows, more so than other snake species, seem very adept at preparing themselves for a shed, utilising heavily their damp hides and water bowls.
Columbians should be treated much the same, slightly lower humidity requirements though, and Argentinean's are far less prone to humidity related problems. I am still an advocate of the moss box though, as in the wild these boas would often root around in leaf litter looking for food and a place to hide.
Cage furnishings are important for enriching their lives, keeping them fit and giving them something to aid shedding but, being terrestrial, branches will rarely be used unless they are thick and near the ground. I call them terrestrial because, with the exception of the Columbian race, I virtually never see them climbing. Having said this there are many reports of animals being discovered in low branches and, in particular, in roof cross members. This could be due to hunting behaviour - lying in wait for bats, birds and rodents.
Don't be fooled by the boa's apparent inactivity: they are nocturnal in captivity (I say that because in the rain forests, where the understory is dark, they might be more sporadic with their times of activity).For all three types it is true that they require lower temperatures than other Boids. Even Brazilians, coming from the equator, don't require upper end temperatures - a facet of living in the dark forests, among the leaf litter and in the moisture. They seem to do fine with a gradient running from 86 to around 76 F, but I would still provide a hot spot of around 88-90 F (the theory being that if it isn't there then they cant use it). Gravid females, and animals fighting infection in particular, will require higher temperatures. Being terrestrial (favouring the ground) I find the use of a heat mat is particularly appropriate with Rainbow Boas.
It is interesting to note that cenchria seem less prone to illnesses brought on by cold and damp, for instance respiratory infections and, specifically, dermal blisters (skin rot). So don't concern yourself too much if they appear to spend a large amount of their time in their moss box.
With a correct environment I have found rainbow boas to be healthy, easy snakes and few complications arise.

Cage size? Rainbow boas are not thickset like other boas, but they can be surprisingly long. Floor area should be the emphasis when constructing caging, as height may not be utilised and just supply volume for hot air to rise into - making heating more difficult. For a Brazilian a six foot cage may be required, so bear this in mind when purchasing your 15 inch youngster.

Feeding:

Poor feeders are rare. If you do come across one then suspect an incorrect environment, for example temperatures too low for digestion, or indeed so warm that the food putrefies in the gut before digestion can take place.
Next try changing their food type. Brazilians are born large enough to take rat pups or small fluffy mice. I have noticed, mainly with green tree pythons, that a non, or fussy, feeder will take the same food item eagerly if it has a little fur. Scenting is the third option, and chicks are the best bet.
In the early stages of their lives anything eaten will quickly be converted into length, but yearling animals will quickly run to fat so stay modest with the feeds, approximately every 2-3 weeks, depending on the individual.
Young Argentineans are the only tricky ones to get feeding, but persistence and all the usual tricks will normally work.
On the whole rainbow boas are very reliable feeders throughout their lives, but always be on the guard for obesity, towards which bored specimens have a tendency.

Breeding:

Boas are viviparous (live bearers), or perhaps better described as ovo-viviparous because there is no placental link between mother and baby. Instead the ova that are released from the ovaries are, to all intense and purposes, eggs without the calcified shell. Their situation is so synonymous with that of an embryo in an egg that development occurs in a membrane, much as an egg has. Just as some snakes may die in their egg for lacking the strength to break free the same can happen with a boa as it struggles free of the membrane post birth. Fertilisation (hopefully) takes place once the ova moves from the ovary into the oviduct.
The prompt for spermatogenesis and follicular development is the typical nighttime lows, as with other boids. Coming from near the equator where there is virtually no seasonal change in temperatures Brazilians, and to a lesser extent Columbians, are not seasonal breeders. So you could use nighttime lows all year round. However it's not necessary and, for health reasons, most keepers prefer to only cycle them when they want breeding to take place. You can keep them cycling until ovulation is observed. Ovulation is the typical extreme mid body swelling which lasts anything from 12 to 36 hours, depending whether both ovaries ovulate, and signifies the release of ovum by the ovaries. Nigh time lows of mid to low 70s are sufficient and lower temperatures should be avoided. Cycling Argentinean's is the same but year round night time lows are not recommended as they are from a range subject to much more seasonal variation. However lower night time temperatures might be required for an animal whose biology seems oblivious to the thermal prompts.
Mating should have taken place by this point and for maximum fertility should be continued for as long as possible.
A hot spot of 90 F needs to be provided for the female whilst gravid, it has been shown that at 93 F gestation can last as short as 4 months, and at low temperatures it can take up to 8 but with a far reduced embryonic survival rate.
All three types can be bred fairly early, two and a half years if large enough, but an extra year is recommended for the health of the female.
They have up to 35 young but 20 is more normal. When breaking free of their embryonic sacks Brazilians are as long as 15-20 inches, vigorous and robust and grow very quickly if fed - up to four foot in a year. When Brazilian young are born they lack the intense colouring of their parents because pigmentation, the last process of development, is not complete. This is nothing to do with camouflage, simply an advantage for the mother who is vulnerable and hungry whilst gravid.

Conclusion:

Rainbow boas make fantastic captives. Within the correct environment they are easy to keep, good feeders and in my opinion the most endearing of snakes in terms of personalities and temperaments.
For those of you who are looking for a beautiful captive, think on about Rainbow Boas. For those of you who like something a little more unusual there are a few proven bloodlines of hypomelanistics and anerythristics out there and even a possible calico.
I hope this article demonstrates how important the geography and climate of the natural range is in a snakes life, and how as keepers we can utilise this knowledge to optimum effect.