By Rob Stone
Introduction & Taxonomy
The longnose, rhinoceros (‘rhino’) or Rhyno ratsnake is a medium sized colubrid snake native to northern Vietnam and southern China, often in mountainous tropical forests in karst regions around waterbodies (Schulz et al., 386-88); between its description in 1897 and the 2014 paper detailed below, it has been a monotypic species within the genus Rhynchophis, but for a duplicative description as Proboscidophis versicolor in 1931 (Fan). The occasionally used moniker Vietnamese longnose ratsnake is disfavored as it implies an inaccurately limited range distribution excluding animals of southern Chinese origin. Save a slight elliptical pupil under light illumination and the nominal rostral appendage, Rhynchophis boulengeri is generally physically comparable to Rhadinophis frenatus, including a similar ontogenic color change process (Schulz et al., 386). To this end, in 2005 one of the first known wild caught Rhynchophis boulengeri to arrive in the United States was imported from China with a damaged rostral appendage; the rostral appendage was nearly disconnected from that male’s face and was removed entirely by the first captive ecdysis (‘shed’), such that save the pupil distinction referenced by Schulz et al., he appeared as a somewhat atypical Rhadinophis frenatus.
In 2014, Chen et al. attempted to clarify the phylogenetic position of the Rainbow Tree Snake Gonyophis margaritatus of Malaysia and Indonesia (Kalimantan), by proposing elimination of the established genera Gonyophis, Rhadinophis (frenatus and prasinus), and Rhynchophis (boulengeri), in favor of lumping the contained species therein with those previously ascribed to Gonyosoma (jansenii and oxycephalum); this conclusion was presented as one of at least three viable taxonomic options to eliminate polyphyly in Rhadinophis while implying a relationship amongst these six species (Id. at 535). This preference for a singular genera comes at the stated expense of ignoring the sister-relationships amongst the taxa, such that the least related species in the broadened genus is Gonyosoma oxycephalum (Id. at 536), the quintessential Gonyosoma species for which the genus was named in 1828.
Having maintained five of the six species described herein (all but margaritatus), I have observed notable physical differences between the three groups of sister-species pairs (535) found by Chen et al. Phylogenetically jansenii and oxycephalum comprise a pair of taxonomic sister species, Gonyophis margaritatus and Rhadinophis prasinus comprise another pair, and Rhadinophis frenatus and Rhynchophis boulengeri comprise a third pair (Id.). As stated above, I have no in-hand experience with margaritatus (I am unaware of any live specimens entering United States herpetoculture in at least the last 25 years), so my experience with that pair of sister species is restricted to Rhadinophis prasinus, which is beyond the scope of this note. However, Rhadinophis frenatus and Rhynchophis boulengeri are markedly different in hand than both Gonyosoma jansenii and oxycephalum.
Rhadinophis frenatus and Rhynchophis boulengeri share generally similar eye and head structures, scalation features, overall body size and morphology (including lacking the air sacks that facilitate a puffed throat defensive display characteristic of jansenii and oxycephalum), and details of egg physiognomy and incubation duration; further, both undergo an ontogenic color change from silver/ grayish brown neonates with black, white, and yellow pattern inclusions to generally green adults. In each instance, these commonalities between boulengeri and frenatus are juxtaposed to differences in jansenii and oxycephalum which have characteristically different eyes, scalation, body form, egg characteristics, and possess an exemplary puffed throat display. Jansenii undergo an ontogenic change where they are born essentially indistinguishable from oxycephalum and later develop their adult black and cream coloration (save the Selayar Islands ‘Black jansenii’ population that maintain the oxycephalum coloration but are subject to a gradual increase in melanin, akin to the ontogenic process of Lampropeltis triangulum gaigeae, ultimately yielding a melanistic animal); this example of an entirely different process of ontogenic change further highlights both the taxonomic sister species relationship between jansenii and oxycephalum and their difference from the taxonomic sister species boulengeri and frenatus.
Accordingly, based on my observation, experience, and predilection to acknowledge commonalities and variation in physical form, my preference is to acknowledge the phylogenetic (Id. at 535-36) and phenotypic relationship of boulengeri and frenatus under Rhynchophis.
Overview
Captive husbandry of Rhyno ratsnakes began in association with a field study led by the Russian Academy of Sciences in Tam Dao and Chapa, Vietnam between 1993 and 1995 (Orlov, 180); I am unaware of any records of this species in captivity prior to this field work and appurtenant collection of specimens. Descendants of this stock collected at Tam Dao, Vietnam comprised the captive lineages of this species, at least in the United States, until spring 2006 when eight adult (6.2) wild caught specimens were imported by Bushmaster Reptiles from China over two shipments, all of which my business partner Tom Weaver and I acquired for High Plains Herpetoculture. Over the subsequent ten years a handful of additional shipments have been received by various importers in the United States, likely consisting of fewer than 50 total animals. There are no known distribution breaks or substantial changes in range condition that would suggest phenotypic variation amongst different populations / localities within this species. In my experience, wild snakes generally have less visible interstitial black or white patterning, giving them a more generally uniform green appearance than captive produced animals.
This species undergoes an ontogenic color change which typically starts between six and eighteen months of age, or upon having at least doubled in length, and can take up to three years to be complete though more typically 24 months (Schulz et al., 386-87). The species is generally considered sexually mature at 1000mm total length (Orlov et al., 8), with an adult size range of 1200 – 1500 mm (Schulz et al., 387); exceptional males older than ten years can attain approximately 1650 mm.
There is no consensus on the purpose of the rostral appendage / ‘horn’; it may be used to “detect fluctuations in water surface movement” associated with aquatic prey items, particularly in neonates and juveniles, or predators (Schulz et al., 390). In captivity they often leave their horn halfway sticking out of the water when laying submerged (Id.). The horn does not appear more sensitive than any other part of the snake: they will freely explore and push it into various positions and crevices; no ill effect or obvious bleeding or deformation was evidenced in the male that shed his horn off, as described above.
Setups
Rhynos are extremely adaptable captives; the species is generally arboreal if the terrarium permits (Schulz et al., 390), but can thrive in terrestrial setups. At present, I maintain adult pairs in Neodesha two-foot cube enclosures with cork bark basking platforms and hides, a container partially-filled with damp long-fibered sphagnum moss, and a water bowl with an indented kraft paper substrate. Cork bark flats and tubes provide hiding places and increase the usable space in the enclosure. These enclosures have UVA bulbs during the warm season (generally mid-March through mid-October in my conditions) and a small refracted flood light during the colder time of year. Run time on these lights varies regularly throughout the year, such that they are on for eight hours a day in mid-Winter and thirteen hours a day in mid-Summer. Previously, I have maintained adults of this species in larger heavily planted display enclosures and sweater-box tubs in racks systems, all to equal success.
When housing more than one individual in a cage, ensure the enclosure is large enough that animals can get far away from any cage mates while remaining in good microhabitats. Males, particularly during breeding season, will engage in combat behavior and aggressively pursue females, including copulatory bites. Multiple males, particularly in the presence of females, should not be maintained together in all but the largest enclosures, as males will engage in aggressive combat behavior including biting. This species sits on elevated perches in a flat coil, akin to Solomon Island Tree Boas (Candoia bibroni australis), rather than a Northern Emerald Tree Boa (Corallus caninus).
I have successfully used a variety of substrates with this species including paper products, shredded Aspen, dry long-fibered sphagnum moss, and cypress mulch; each have benefits based on the relative humidity in your location, though all must be able to drain thoroughly. These are generally problem free and hearty snakes; however, they are susceptible to skin decay if kept too moist or in a dirty environment. Using a particulate substrate like shredded aspen or cypress mulch, enclosures should be spot cleaned when waste is observed. If using a solid paper substrate like paper towels or newsprint, the whole sheet should be changed. The substrate should be kept dry for juveniles and adults and may be kept lightly moistened for neonates.
I utilize an 8-ounce disposable water cup for this species at all ages; in adult display enclosures I use them as disposable liners to ceramic bowls. Generally, females of this species tend to soak more than males, though this behavior overall has decreased to essentially never in my collection over the last five years. Based on observations of neonates and juveniles, I believe the greater tendency for females to soak is a reflection of breeder’s tendency to offer more food to mature females than mature males; in my collection neonates and juveniles soak for 24-36 hours after consuming heavy meals relative to their size (even a mouse pinky will elicit this behavior in neonates), presumably / inferentially the snakes exhibit this behavior to decrease the weight burden of the food bolus akin to the reduced weight and gravitational pressure associated with floating in a pool.
These are very hardy snakes that do well at most temperatures between 60 and 82-degrees Fahrenheit. Especially as neonates, they are susceptible to overheating if exposed to continual temperatures above 85 without an opportunity to reach cooler temperatures. If ambient temperatures are below 75 continually, a basking spot that allows them to reach 85 to 90-degrees should be offered for at least some portion of the day, either using an under-tank heat pad or elevated basking spot and low wattage bulb. During the periods of activity observed by the Russian Academy of Sciences field study, temperatures in Tam Dao, Vietnam ranged from approximately 78 to 84 during the day and 62-70 at night (Orlov, 180). In the wild, Orlov et al. (8) reports the species to be nocturnally active during the first half of evenings from April through June when temperatures were approximately 68-80 with elevated inactive basking behavior during the day. In captivity the species tends to be diurnal, basking and actively moving during the day, particularly when the temperatures in the enclosure correspond to those described in the wild above, though crepuscular behavior is common April through August.
Maintenance
Established Rhynos readily feed on rodents; the Russian Academy of Sciences field study found faeces in the wild contained rodent hair, and large animals were found with scars from apparent rodent bites (Orlov et al., 8). The species generally prefers multiple smaller food items such as half-grown to weaned mice (Schulz et al., 390), whether in a single offering or one at a time over a condensed period of several days.
In my collection this species feeds seasonally, with mature animals eating between mid-March and mid-October. Males typically fast after brumation through the time females ovulate or even lay eggs (typically this is mid-March through June/ July in my collection); this can result in mature males going eight or nine months without feeding without detriment. Females generally eat readily as the weather warms in spring, fast once they begin to develop enlarged follicles, and eat readily upon egg deposition. I prefer to feed crawler or hopper mice to my adults; there are times of year when my adults will feed on a single item daily for seven or eight days in a row. I maintain neonates and juveniles with access to supplemental heat year-round, so they are offered an appropriately sized (bearing in mind the predilection for smaller items) mouse once every five to fourteen days. Typically, at least by the time their ontogenic color change is initiated (six to eighteen months) Rhynos feed aggressively on frozen/ thawed items offered on hemostats.
It is imperative not to overfeed Rhynos; this species tends to develop masses of dead cells between the muscle and skin if overfed. This appears to be a product of an inability to process excess fat when domestic rodents are offered at too frequent a rate; this issue is exacerbated by feeding overly-large rodents. These masses of fat and dead cells have appeared to cause, or develop into, fibrosarcoma tumors that can appear over the snake’s body. Sometimes this species will be offered for sale showing a dark stain in the center of each scale over portions of the snake’s body; this is usually a product of previously having had scale degeneration or subcutaneous masses in the affected area, and occasionally may be accompanied by a distortion or elongation of the scale structure.
Once established feeding, and often around the time of their ontogenic color change, this species can become food aggressive, often lunging out of their enclosure open-mouthed for food. For animals that display this behavior, it is useful to hook them out of the enclosure, at which point they will be completely tractable. Captive bred juvenile and adult specimens do not bite out of aggression; all bites I have received have been the result of a food mistake. Some neonates will bite defensively, particularly when restrained, but these are inconsequential. Wild caught specimens generally are much more willing to bite defensively than captive bred specimens, though it is still uncommon. On the rare occasion of a bite from this species, I have not observed any complications or effects, unlike bites from Gonyosoma oxycephalum and jansenii, both of which seem to have some negligible anticoagulant properties in their saliva. This species does not tend to bite once in hand, and does not tend to bite the hand restraining it, unlike many of the Oreocryptophis porphyraceus ssp.
These shed on a fairly regular basis: perhaps three or four times a year in adults, and up to five or six times a year as juveniles. They take a relatively long time to shed after going opaque compared to other species; they often take 10 to 14 days between initial cloudiness of the spectacle being observed to ecdysis. They should shed in a single piece without complication as long as they have access to drinking water during the period of opacity. This species has thick and durable scales compared to other colubrids; it is resistant to most damage besides bites from conspecifics during breeding attempts (males of this species utilize a copulatory bite on females that can result in pronounced wounds, particularly if the female’s skin is weakened).
Reproduction
This species generally matures slowly if fed conservatively; males may breed at 2.5 years of age, but females often will not breed successfully until they are 3.5 or 4.5 years of age. Both males and females tend to grow to their mature length of approximately 1000mm (Orlov et al., 8) before attaining their adult girth; some females do not attain their adult proportions until the hormone shift associated with being paired for breeding. I am not aware of anyone ever successfully double clutching this species in a single breeding season. Fertility is typically best in animals younger than 10 years old, though I have had success with males and females in their mid-teens.
Though some report success breeding this species without subjecting them to deliberate seasonal temperature or light cycle variations (acknowledging intrinsic ambient seasonal pressure and humidity changes), my best results have been achieved utilizing a seasonal cooling period between November and March, where the daily temperatures fluctuate from the mid-50s to low-70s with brief isolated access to temperatures into the 80s should the animals desire it. I have observed this species active, though their movements are exceptionally slow and deliberate, at 38-degrees Fahrenheit. It is generally inadvisable to leave this species at a constant temperature below approximately 52; variation in temperature mimics their natural range and prevents the possibility of neurological damage occasionally observed in Rhynos kept consistently cold throughout the cooling period.
In the wild, gravid females have been observed in May and June (Orlov et al., 8). In captivity, eggs are typically laid between June and early August (Schulz et al., 387), though I have had some females that regularly laid as early as late April. Rhynos generally lay five to fifteen (typically six to eight) elongated eggs (Id.), often stacked together in a packet (Orlov, 180), which is laid either horizontally or vertically inside a cavity or hide. The largest clutch in my collection to date consisted of seventeen eggs; interestingly, there is greater variation in egg consistency (size and shape) as the number of eggs increases. Most clutches in my collection of six or seven eggs appear as uniform packets, while those over twelve or thirteen tend to produce a variety of egg dimensions including some that are nearly circular.
Fertile eggs are typically deposited ten or eleven days after completion of the post-ovulation shed (Schulz et al., 387). It is common to have unfertilized or non-viable eggs laid inside or accompanying the post-ovulation shed when these are nearest the vent. Such non-viable eggs can be laid throughout the period preceding the anticipated time of egg deposition; generally, eggs laid sooner than seven days after the post-ovulation shed will not be viable. Occasionally, follicles will get so large before ovulation that they will induce a pre-ovulation shed; in such instances it is possible to get two sheds from the same female within a five or six week period, with egg deposition coming approximately ten to fourteen days after the second shed.
As a note of potential distinction relative to most colubrid species, after egg deposition females will regularly encircle and seemingly guard their eggs or lay adjoining them in narrow/ essentially inaccessible places for at least a week; I cannot say how much longer they would remain with them, as I’ve never left the clutch in situ longer than a week to avoid egg desiccation. Interestingly, even once the eggs have been removed the females seem to have a very strong affinity for the spot of egg deposition.
Anecdotal evidence suggests genetic sex determination may be overridden by incubation temperature in Rhynos, as well as the Oreocryptophis porphyraceus ssp.; novel access to commercial genetic sex determination for colubrid snakes is certainly intriguing to examine and potentially validate this phenomenon previously known in other reptiles but not validated in snakes. Initial herpetoculture of this species utilized higher incubation temperatures of 82.5 to 84-degrees with offspring hatching after 57-61 days (Orlov et al., 6); in my experience this tends to lead to the production of a higher number of males, as well as non-viable or deformed offspring. 78-degrees is a generally-accepted safe incubation temperature that generally produces an approximately even sex ratio. I have incubated a clutch at variable temperatures in the 60s Fahrenheit; the offspring, all of which were female, took twice as long to hatch (117-121 days). I have utilized a variety of egg incubation methods successfully including half-burying eggs in damp vermiculite or perlite or suspending them on light-diffuser panel over either water, saturated particulate substrate, or damp long-fibered sphagnum moss.
There are no identified and proven single gene mutations in Rhynos as of this writing. Since the Russian Academy of Sciences field study there has been a report of a single mature animal that had retained its neonate coloration (Schulz et al., 388). In general, the normal male phenotype presents as a green snake with yellow ventral scales, while females tend to be green or bluish green snakes with white ventrals. Some of the original captive stock descended from Tam Dao animals have a propensity to produce blue, bluish green, or turquoise adults (Id.); this appearance appears to be inherited polygenically. Additionally, like Green Pythons (Morelia viridis complex), a blue phenotype is possible through reductions in the amount of yellow-appearing pigment. Reproductive cycling and egg production in females appears to utilize hormones that either produce or cause yellow pigment to be present in the skin, causing mature females to become continually more ‘hormonal blue’ with each consecutive clutch. Accordingly, determining a truly genetic blue mutation would benefit from the production of phenotypically blue males, which necessarily will not be ‘hormonal blue’ at least pursuant to the same mechanism. Finally, exposure to UV-light has anecdotally been observed to cause green animals to appear bluer or vice versa in some lizard species including those in the genera Abronia and Crotaphytus.
Neonates average 6mm in diameter and are approximately 250mm long (Schulz et al., 387). In light of their thin proportions, newborns are best kept individually in lidded enclosures or tubs; newborn Rhynos can escape from exceptionally small tolerances between tubs and a rack system. Neonates occasionally will eat other neonates when kept in groups. They can be hesitant to start feeding on rodents. Some breeders report success leaving frozen/ thawed pink mice in the enclosure or floating them in the water bowl. Historically, I tease-fed reluctant feeders pink mouse heads offered while holding the snake in my other hand to limit a flight behavior response; this is effectual for snakes that will bite and hold the prey item, but not valuable for ‘runners’ that cannot be provoked into a strike response or those that strike and immediately release. Now, I offer live fish or tadpoles to those that will not voluntarily feed on mice, sequentially reducing the number of alternative feeders offered and replacing them with a floating frozen/ thawed pink. This transition process is typically effectual and avoids unnecessary stress on both the snake and I. Neonates shed between one and two weeks after hatching; the rostral ‘horn’ is typically flattened to the top of the head upon hatching to expose the egg tooth and flattens out after the first shed (Schulz et al., 387). There is variation in horn length and shape, and the angle at which it extends from the face, all of which seem to be inherited polygenically.
References / Bibliography
Brachtel, N. (1998): Rhynchophis boulengeri Mocquard. – Sauria, 20(1): 2.
Chen, X., McKelvy, A.D., Grismer, L.L., Matsui, M., Nishikawa, K., & Burbrink, F.T. (2014): The phylogenetic position and taxonomic status of the Rainbow Tree Snake Gonyophis margaritatus (Peters, 1871( (Squamata: Colubridae) – Zootaxa, 3881(6): 532-548.
Fan, T.H. (1931): Preliminary report of reptiles from Yaoshan, Kwangsi, China – Bull. Dept. Biol. Coll. Sc. Sun Yatsen Univ., (11): 1-154.
Orlov, N.L. (1995): Rare snakes of the mountainous forests of northern Vietnam – Russian J. of Herp., 2(2): 179-183.
Orlov, N., Ryabov, S. & Schulz, K.-D. (1999): Eine seltene Natter aus Nordvietnam, Rhynchophis boulengeri Mocquard, 1897 (Squamata: Serpentes: Colubridae) – Sauria, 21(1): 3-8.
Schulz, K.-D., Ryabov, S. & Wang, X. (2013): A contribution to the knowledge of the Oriental rhino ratsnake, Rhynchophis boulengeri Mocquard. In: Schulz, K.-D. (ed.): Old World ratsnakes – A collection of papers. – Bushmaster Publications, Berg SG: 385-394.
