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About the Argentine Boa, Boa c. occidentalis

Argentine boas can be quite large, females especially are among the heaviest of the Boa. A 12 year old captive female specimen of 3 meters with a mass of 28KG is reliably reported. Average mature adults are more moderately proportioned. Adult breeding males can be well under 2 meters and females giving viable births may be only slightly larger. In culture we see mostly charcoal-black or deep mocha colored occidentalis, with silver or gold residual saddle patterns visible to a greater or lesser extent. In nature there is more variation. The hissing and mock-attacks of small Argentine boas are quite entertaining and are virtually always overcome in a short time with patience and gentle handling.

Boa constrictor occidentalis is critically endangered in nature due to habitat loss and degradation. The temperate forests and rocky slopes where they are still holding out are cut for fuel or materials and mined for hard-rock mineral deposits. Major universities there are pioneering efforts to save these unique animals from extinction through captive reproduction and ultimate reintroduction as a last-ditch attempt to keep them from disappearing from the wild.

Here in the United States breeding programs have been very successful. So much so that the average price of a nice baby Argentine boa has plummeted in the last several years. In the minds of some breeders and dealers these unique snakes have been relegated to junk-commodity status and there is little incentive to preserve occidentalis in culture. It is left to the keepers and breeders who love these great Boa to work to keep them viable in captivity. Inbreeding should be carefully monitored. Carefully examine your motives before out-crossing or intergrading pure occidentalis with other subspecies of Boa. Due to the uniqueness of the Argentine subspecies and their rarity in nature I offer this detailed essay on the culture of the occidentalis.

A guide to the keeping and breeding of Argentine boas.
Argentine boa are considered to be easy to keep and of only moderate difficulty to breed at our latitudes here in the U.S.. Temperature manipulation may be a key factor in breeding. In addition due to the very limited availability of new genetics from nature there are many 3rd or even 4th generation animals in the hobby population. These successive generations have in some cases become progressively more adapted to culture and somewhat less demanding to breed. Here’s a short description of my current occidentalis project.

As of this writing the adults I have now are F1 and F2 of wild-collected animals and have been reliable breeders. A litter in the 2004 season consisted of 37 neonates, 52 to 55cm in length and quite massive, there are 19 males and 18 females. This particular female (8-1/2 years of age at breeding) is 2.5 meters long with a mass of 12.9KG at the height of her pregnancy, this was her largest clutch to date, the 4th in 4 years, her first was the smallest, 19 babies. In 4 litters she has dropped only one infertile egg and one non-viable baby and has maintained a near 50/50 male/female ratio in her offspring. These results are typical.

Except during the time when she is guarding and nursing her young she is entirely docile and a fine captive specimen in all ways as is her mate. I consider this last observation important, insecure Boa of various subspecies are often less likely to deliver the best litters in culture. Find the right conditions for your boas so that they are calm and secure. 

Care of growing Argentine boas.
These boas do not require conditions or temperatures much different from other small Boa constrictors. They may benefit long term from a winter-summer temperature change even while small, more so than common imperator  locales. Argentine boa neonates are very good feeders. Practically all baby Argentine boas born here accept pre-weaned rats or medium mice on their first feeding attempt, 5 or 7 days after their initial ecdysis. Once established in a routine these can eat and digest more prey items of comparatively larger size and mass than any other Boas in my experience. And they can do so while maintaining a normal length-to-weight ratio, not quickly becoming obese. Still, you must watch for signs of obesity and modify the feeding if it occurs. And note also, you do not have to grow giant Argentine boas (or others) to successfully produce young.

Typically, occidentalis are born later in the summer than common boas. But even with some seasonality supplied during their first years of growth they may be well within breeding size by their third winter and breeding trials can be safely attempted. I have had excellent results waiting for their fourth season.

Breeding observations.
The occidentalis in my care require a well-defined temperature gradient, both seasonally and day/night for successful breeding. This is accomplished with thermostatically controlled substrate (under-cage) heating. Courtship starts in late December or early January after two or more weeks of temperatures 15-20% lower than those experienced at the height of the growing season and may continue until late February. Intromission can occur both at mean low temperatures and during temperature rise but has not been observed at body temperatures below (approximately) 68 degrees (f) or above 84 degrees (f). However, copulation is sometimes not prolonged and may go unobserved. Ovulation in occidentalis is of noticeable proportions and as soon as intromission and ovulation is confirmed the cool temperature cycle is reversed and returned to normal levels.

Gravid or incubating occidentalis are provided a substrate heat source approximately as large as the resting specimen of nearly 100 degrees (f), a refuge from the heat is also always available. They move little in the early stages and thermoregulate in subtle ways by alternately raising or lowering the mass of their bodies on the heat, something which may not be available to them if heat lamps or other radiant heat sources are used.. Mid-body temperatures of 96 degrees (f) have been observed in incubating mothers in the first 1/2 of the incubation period. Almost all Boa, including occidentalis will abandon (to some extent) the heat source during the last 3 to 5 weeks of the incubation if ambient temperatures of over about 85 degrees (f) are available. A thermal gradient in the enclosure allowing gravid boas to closely regulate their body temperatures may be very important. If during incubation the female appears interested in feeding (as is usually the case) we will allow moderate meals. Care should be taken to avoid feeding meals too large, too frequent or too near parturition.

Under the above conditions occidentalis  have delivered young as soon as about 115 days and as long as about 150 days after a post-ovulation shed-cycle.  These are in my experience very good mothers, they carefully prepare a nest site in the substrate and systematically check and nudge each baby, perhaps encouraging movement or breathing. If bothered, mother occidentalis will energetically guard their young and also mound the substrate in such a way as to hide the presence of the babies. Newborns are a plain slate or blue-grey. Darker pigments develop minutes after they begin to breathe on their own. It is our practice to leave mother and young undisturbed until the babies begin to disperse as long as no problem is observed. Contrary to some opinion, healthy baby boas, including these, rarely require any assistance in leaving their birth sacs. Individuals may suffer harm from being taken from their eggs if they are slightly pre-mature. Occidentalis in particular may wait for many hours before pushing an opening (22 hours is the record here).

     – A. Rentfro, RioBravoReptiles.com
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