Boa nebulosa

Scientific Name

Boa nebulosa 
Boa nebulosa
Described and named by Josephus Nicolaus Laurenti (1735-1895), an Austrian anatomist and zoologist.  He is remembered as the "Father of Herpetology."
Re-described and renamed by James Draper Lazell, Jr (1939-) in 1964.

Holotype

Museum of Comparative Zoology (MCZ) no. 65493, J. D. Lazell, Jr. collected 30 July, 1959. Paratypes: MCZ no. 65494, same data as the type; MCZ no. 65492, Moore Park, Dominica, J. D. Lazell, Jr. collected 21 June, 1958; MCZ no. 65495, Layou Park, Dominica, J. D. Lazell, Jr. collected 14 August, 1959; MCZ no. 58772, Trafalgar, Dominica, J. D. Lazell, Jr. collected 18 June, 1958; MCZ no. 74371, Trafalgar, Dominica, J. D. Lazell, Jr. collected 18 June, 1959; MCZ no. 6106, Portsmouth, Dominica, S. Garman collected 1879.

Type Locality

Woodford Hill, Dominica.

Subspecies

None

Synonyms

The name nebulosus is in allusion to the extremely dark, clouded appearance of the boa.

*  Du Tertre prefaces Volume I of his IV volume work with:  The first edition of this work, “or rather the project of it, which the author was obliged to put in press in haste because he understood that some other person was about printing it under some other name,” was published at Paris in 1654 under the title, Histoire generale des isles de S. Christophe, de la Guadeloupe, de la Martinique, et autres dans l’Amerique, (Preface, vol. I) .

Common Name

Clouded Boa, Dominica Boa, Dominican Boa, Tet’chien.

Taxonomic history

The boas from the Antilles have been documented long before the adoption of Linnaeus’  system of classification.  As early as 1564 Rene Laudonniere landed on Dominica to take on fresh water and other stores, in continuation of a rescue voyage consisting of 3 ships under his command.  He wrote, “it happened on a day that certaine of our men desirous to see some new things in these strange countries, walked through the woods: and following still the litle rivers side, they spied two serpents of exceeding bignes, which went side by side overthwart the way.  My souldiers went before them thinking to let them from going into the woods: but the serpents nothing at all astonied at these gestures glanced into the bushes with fearful hyssings: yet for all that, my men drew their swords and killed them, and found them afterward 9 great foote long, and as big as a mans leg” (Hakluyt, 1904).

In 1620 a Boa was mentioned by the Corsair Apothecary  known as “The Anonymous de Carpentras” who lived in both Dominica and Martinique at the time.  The writer failed, sadly, to indicate which of the two Islands he was referring to when he wrote: “They have a very long and flat head, and a very slit mouth where they have three or four large front teeth like those of a dog.  He was told by the local population a large snake would come down from the mountain after high winds (cyclones) to prey on hens.  He adds that “When they want to eat a hen”  they “get so entangled around her that they prevent it not only from flying but from moving.”

In 1635 Father Breton came to Guadeloupe and stayed 12 years amongst the Native population.  After returning to France he published, in 1665, the famous “Caribbean-French Dictionary.”  He wrote: “Ouanache is a great Dominica Serpent that is more than three ells long, which swallows a rooster or a whole hen, the bites of which are very painful but not fatal” .

Father Du Tertre, in 1667, writes of the Dominican Boa:  “There is another source of it in the Isle of Dominica, which is never bigger than the arm, and which is nevertheless ten or twelve feet long: this serpent usually throws itself on the hens, & in a wink twists around them, & without biting or stinging them, shackles them with so much force, that it makes them die, & swallows them on the run as they chew them .

To place the taxonomy of the Dominican Boa in perspective, we need to understand how we “got here from there.”  Lazell, visiting Dominica in 1958 described the boa as a “big fellow that more closely resembles the South American Boa constrictor than anything else.”  He stipulates, however, “it is very different in body proportions and in coloration and in pattern” .

According to Lazell (1964), the oldest available name for a Lesser Antillean form is Boa orophias (Linnaeus, 1758).  The ventral count provided without doubt assigns the name to the Saint Lucian boa since no other boa in the genus has 281 ventral scales.  The name diviniloqua, used by Dumeril & Bibron (1844) was originally assigned by Laurenti in 1768.  Lazell then reasons diviniloqua, sensu Dumeril & Bibron, is a junior synonym of orophias.  Diviniloquus, sensu Laurenti does not apply to any other Lesser Antillean boa.  Of the two boas, Saint Lucia and Dominica forms, it could only apply to orophias.  The few Dominica specimens in collections have always been referred to as orophias.  In 1935 Stull combined the Saint Lucia and Dominica forms under orophias and differentiated them at the species level (Constrictor orophias).  No name had ever been proposed for the Dominica Boa.

Since Boa nebulosa had long been synonymized as Boa orophias due to its close geographic proximity to Saint Lucia, no one bothered to closely look at the boa for well over a century.  Several elders of taxonomy gave mention to the Dominica Boa but were not prepared to make any changes, taxonomically .  Lazell (1964) took it upon himself to separate both Boa nebulosa and Boa orophias; he renamed them sub-specifically, treating them as subspecies using the stepped-cline series as geographic variations in a single species.

Boa nebulosa, Scottshead, Dominica, Photo Ricky Lockett

Price and Russo (1991) recommended the Clouded Boa be elevated to full species in their description of Boa constricor longicauda.  Bosch (1994) recommended elevating the Dominica Boa to full species.  In 1998 Walls considered the Clouded Boa a full species as well.  It was not until 2007, when Bonny made a relevant and substantial case for the elevation to full species that the Tete’ Chien was finally recognized as a full species.  Henderson and Powell agreed with Bonny, acknowledging his work in 2009 .

Description and taxonomic notes

Dorsal scale rows at mid-body 59-69, ventral scales 258-273. Obscure, irregular dark dorsal bands numbering 32-35 to the vent.  Ventrally dark, clouded and gray-brown.  Venter to tail ash to slate gray, mottled with black.  Subocular and loreal striping missing or mostly obscure; chin and infralabials gray.  Snout prominent with a convex canthus .  Generally light grey, grey-brown to dark chocolate.  The tail pattern consists of light yellow to orange markings.  The coloration darkens with age to a very dark chocolate brown.  Some snakes appear almost unicolor.  The boa is capable of changing its coloration from dark to light, as many of the C. striatus are capable of.

Honegger (in Lazell 1964) reports a clouded boa of 3 meters in length .  Angin found a 3 meter long specimen in the wild .  The largest specimen in the collection of Bonny had a length of 2.30 meters , Malhotra et al. report that Boa nebulosa reaches length up to 4 m .

Distribution

Dominica (of the Lesser Antilles). The island has a total surface area of 790 km2 and the highest elevation is 1438 m high. Boa nebulosa occurs throughout the island and up to 350 meters in elevation.

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Habitat

Mean annual temperature on Dominica is 24.11°C.  Mean annual precipitation is 3037.15 mm.  The island is 24 km at its widest point and 48 km long.  There are several peaks that exceed 1000 meters and they are spread from the northern tip of the island to the southern end.  The highest point on the island is Morne Diablotin, rising to 1447 meters above sea level.  The peaks can receive more than 10,000 mm of annual rainfall .

Roseau, Dominica. Harris, 1837
Boa nebulosa habitat. Photo Sebastian Holch

The island experiences the year‐round warm, humid conditions associated with a maritime tropical climate.  Mean monthly temperature on the northeast coast has a low of 18°C-20°C and a high of around 28°C-31°C.  During the warmest period of the year, a maximum of 33°C may be observed along the coast, compared to 27°C in the mountains.  The wet season occurs from July to January, during which the island receives around 1250 mm annually on the northwest coast .

Boa nebulosa in situ. Photo Sebastian Holch

El Niño episodes bring warmer and drier than average conditions between June and August and La Niña episodes bring colder and wetter conditions at this time.  Heavy rainfall associated with cyclones and hurricanes contributes significantly to wet season rainfall values.  The occurrence of hurricanes is strongly linked to el nino’ events, with more frequent hurricane activity associated with La Niña events.

The boas were at one time amazingly abundant on the island of Dominca.  They are found in forest, disturbed forest, montane forest and xeric woodland; here they are limited to wet ravines such as the south tip around Scott’s Head.  They are often encountered up in trees (large adults being the exception).  Three to twelve animals could be found congregating in a large hollow tree log and are often found along the edges of machine cleared banana fields .  Du Tertre (1667) states they appear more frequently in the months of May & April.

Two Boa nebulosa on Dominica. Photo Sebastian Holch

Wilkins (pers. communication) as well as Vandeventer report that the boas can also be found in numbers located by steam vents.  The Boas aggregate in “cavalesche tete’chien”, which is best translated as “snake tunnels”.  These structures are piles of rocks, a root system, or most frequently, a shallow undercut in a stream bank.  The site is in full sun but shaded by tall sedges and grass.  All were in the immediate vicinity of hot springs and sulfur gas vents along volcanic mountain streams .

A dark specimen in situ. Photo Sebastian Holch

Daniells et al. found these snakes in woodland and montane forests, scrub, and on vegetated cliff faces.  According to them, B. nebulosa can only be found sometimes in more disturbed areas, such as along the edges of banana fields .  This observation is in contrast to Lazell, as well as Bullock and Evans, who found that the snake is widespread and frequently encountered especially on roads and on land recently cleared for cultivation . During a recent study, McNames et al. found two boas in different habitats. The smaller specimen 134cm SVL was found near Batalie Beach in dry forest ca. 6m high in a tamarind tree. The larger boa (191 cm SVL) was found on a road in a littoral forest near Castle Bruce .

Boa nebulosa in habitat. Photo Sebastain Holch

Bullock and Evans found B. nebulosa in coastal woodlands, where they observed the highest reptile biomasses.  The incongruity in the observations between Lazell and Bullock and Evans versus Daniells et al. might be explicable by potentially intensified agriculture with severe use of pesticides and herbicides.  The observations have more than two decades in between them and in this time period agriculture and the use of chemicals have changed tremendously.  It will be informative to investigate links of population decline with changing agricultural practices and other human impacts on habitats.

Boa nebulosa
Clouded Boa
Boa nebulosa
Clouded Boa
Dorsal color and pattern of the tail.

Longevity

We assume Clouded Boas can live equally as long in situ as its congeners.

Reproduction

The Glasgow Zoological Gardens (now extinct) bred Boa nebulosa three times while they were in operation as noted below :
1988 GLAS 0.0.9 born during 1988.
1990 GLAS 0.0.3 born during 1990.
1991 GLAS 0.0.4 born during 1991.

The few publications on the reproduction of Boa nebulosa suggest that the litter size is significantly smaller than that of Boa constrictor, ranging from 6-25 babies.  Gestation time is about the same as B. constrictor.  Breeding seems to occur in the months of March and  April with young born in July and August.

Boa nebulosa mating. Photo Sebastian Holch

Vandeventer and co-workers could not find baby boas during their trip to Dominica in February 1990. .

Boa nebulosa copulating. Photo Sebastian Holch

Schwartz and Henderson report that 16 nearly full term developed young were removed from a female in April .  A wild caught Boa nebulosa gave birth to 15 young in July .

Gravid Boa nebulsa. Photo Sebastian Holch

Behavior

The Clouded Boa is still poorly understood by institutions and private collectors alike.  In captivity, the boas have the reputation of being very aggressive as babies and youngsters but normally grow out of their irritable nature and tolerate occasional handling.  Of course, there are always exceptions to this and the rare boa will maintain its irascible nature into adulthood.  Boa nebulosa are very insecure and will wrap anything and everything within their grasp, making handling them very difficult.  In captivity, when not basking, they remain hidden during the day.  In the evening they will extend a small length of their body from their hide and watch/wait for food.  Except when feeding, the boas move with a slow and deliberate crawl.

Interestingly, Vandeventer reported that he found the boa exclusively in groups of two to seven animals in the wild.  Only on one occasion did they find a single female  alone (in preparation to shed) .  Wilkins (pers. communication.) confirmed this behavior.  This is an interesting phenomenon and might point to a behavioral uniqueness of this boa.  The fact that the Dominicans have given this behavior a name (snake tunnels) indicates that these were not anecdotal observations.  While the most parsimonious explanation of this behavior might be  a link to breeding season, we could also imagine that some hidden social life is occurring in this species.  It should be added however, that neither Lazell nor Angin reported group aggregations of these boas in the wild .  This might also be an artifact of the breeding season.  Further study in situ is needed to fully understand the life cycle of this magnificent boa.

Diet

Lazell found that Boa nebulosa preys on rats exclusively, even though agoutis (Dasyprocta sp.) are commonplace.  Angin reported bat predation by the Dominica boa: “The boa caught a bat, later identified as Brachyphylla cavernarum, and constricted the prey with the middle of its body while trying simultaneously to catch other bats” .  Daniells and co-workers claim that the diet consists of small vertebrates such as agoutis, iguanas, and chickens .  Oddly enough, they don’t name rats as prey items which have been found the preferred prey by Lazell.  In addition, they didn’t provide a source for their claims.

Bonny found young B. nebulosa in trees like Lazell did before him .  He suspects that young B. nebulosa feed on lizards and birds.  While all these claims appear reasonable, they show the limitations of our knowledge since detailed stomach content analyses and more detailed field observations are missing.  In captivity the boas take appropriately sized mice and rats, fowl and rabbits.  J. Murray found, quite by accident, that feeding the adult boas rabbits almost always made it impossible to get the adults to feed again on rodents.  Keep this in mind when contemplating rabbits as a food source.

Captive management and captive population

The history of Boa nebulosa in captivity reaches back more than 70 years, when the Philadephia Zoo produced what is supposedly the first captive breeding of this species in 1958 from animals collected by Lazell in 1958 (and 1959).  This was the first time the boas had been seen alive in the US .  Subsequently the boa was imported several times as can be seen from old price lists and kept by private persons as well as in some zoos.

Neonate boa nebulosa. Photo Sebastian Holch

In recent history Boa nebulosa were imported into the USA by T. Wilkins (ca. 1989) and in 1990 by T. Vandeventer.  The latter told the story of his line of Boa nebulosa during a conference.  In February of 1990, he imported together with Robert A. Young and Tyler Miller five adult pairs of these boas.  He describes the capture, importation and breeding.  Their boas, which were housed in two groups (2.2 and 3.3), bred during the latter part of March through most of April, resulting in four females ovulating.  The gestation period was about four months and litters were produced in late July and August of 1990.  Litter sizes were 7, 9 and 11 and the neonates were on average 17 inches (43,2 cm) long.  A fourth female produced 13 infertile ova and one premature neonate in early July.

Last known breeding of Boa nebulosa. Photo by Sebastian Holch.

The babies, which were more vividly marked than their parents, were difficult to start feeding and despite great efforts, three baby boas did not survive.  After the initial breeding no further reproduction of the wild caught stock took place.  Standard techniques used to stimulate breeding have been ineffective .  The litter size described is similar to what Bonny reported .

Juvenile female Boa nebulosa in its “light” phase.

Second generation breedings by B. Harding and T. Mead took place in the late 1990’s using the offspring produced by Wilkins and Vandeventer.  The whereabouts of the offspring are unknown at this time.  In the EU the species was bred by K. Bonny, S. Holch and others.  The whereabouts of the offspring are unclear.  While these reports of collection and subsequent captive breeding of these boas are a true success story, it should be noted that the same cannot be said for many of the other Boa nebulosa that made it into the hands of private collectors.

While a few collectors have had very good results in breeding and maintaining the boas, most died fairly quickly.  One possible explanation lies in the temperature regimen the keepers provided for their boas.  The boas are very heat tolerant as noted by being found near steam vents.  It is possible that the boas were never provided access to proper heat gradients, i.e. heat levels that would prove fatal to many other boa species.  Clouded boas in the possession of J. Murray sat under heat lamps at least once daily, sometimes twice after feeding, and “baked” for long periods at temperatures of 96° F – 98° F (35.5° -36.7° C.) with no ill effects.  Failure to provide access to the high temperatures always resulted in the boas going off feed.

Typical basking temperature of a non-gravid female.

Stöckl and Stöckl write on their website about the captive history and breeding of Boa nebulosa in Germany.  The initial breeding stock was obtained by a German breeder in Munich from the Netherlands.  He managed to breed the boas several times but eventually discontinued breeding efforts.  Stöckl and Stöckl note that Boa nebulosa tend to develop back problems in captivity .  In the light of J. Murrays observations in captivity and the observations on the islands made by Vandeventer and Wilkins, it might be speculated that these back problems are linked to an improper heat regimen which might provoke a form of gout in these boas.  Whatever the real cause, there are too few boas ex-situ to study and determine the cause of this condition.

To summarize: the species was kept and bred in small numbers in the US and Europe, the current situation for the captive stock doesn’t look promising. Only very few animals exist today in captivity and we hope that keepers and breeders will collaborate to establish a self sustaining reproducing population ex situ. We feel this boa is a good candidate for legal export from the Island and placed in ex situ breeding programs undertaken by responsible institutions and collectors in the private sector.  This boa is a prime candidate for the Invisible Ark.

Conservation, threats and population size in the wild

CITES:  Appendix II
Dominica joined CITES on 4 August, 1995; entry into force on 2 November, 1995.

IUCN Red List:  Least Concern (LC)

Catalogue of Life:  (click here)

The National Center for Biotechnology Information:  (click here)

CITES import/export data:  (click here)

The 20 July, 2015 rating of LC by the IUCN is provided as follows:

Listed as Least Concern on the basis that, while, this species has a restricted range and may be subject to some degree of persecution and, at a low level, collection, it is regularly encountered in surveys and there is no evidence of decline. As forest cover is presently stable and this species is not a forest obligate it is not subject to a continuing decline in the extent or quality of its habitat.

Lazell noted that the snakes were amazingly abundant on the island of Dominaca .  Bullock and Evans note that B. nebulosa is widespread and frequently encountered especially on roads and on land recently cleared for cultivation .  Malhotra and co-workers noted that  the Dominican boas are apparently not considered very attractive for the leather trade thus they are not under threat from this side.  They found Clouded Boas to be widely distributed in Dominica and still fairly common, however noting the possibility that larger individuals are becoming less commonly seen .

Rescued Boa nebulosa after taking a large prey item. Photo Nick Pollock
Pollock remarks: "I took the photo as I was walking up Imperial Rd from Canefield, heading towards the biological field station we were staying at. The road winds through small houses and shacks as it works upwards in elevation, through tropical forest. I passed by a house and at the end of the driveway was this boa with a piece of twine tied tightly around it's neck (a local must've done it to drag the snake out from near their house). The poor snake had a huge air bubble in its neck, as it couldn't exhale it, and was clearly in distress. I had to cut the twine off the snake's neck so it could breathe and survive. I then moved the snake away from the house to get it away from anymore potential harm. I'm not sure what was in its belly, but it was about the size of a large agouti or even a large cat".

Several authors mention that humans hunt them for snake oil, a locally prized remedy for low libido and rheumatic pains and kill them because they are preying on domestic chickens.  Malhorta et al. also mention road kills as a conservation concern.  Reynolds and Henderson disagree with IUCNs view of this species being of Least Concern and advocate that the species should be assessed as Vulnerable (VU) .  We have seen no evidence of any study indicating the population numbers on the island and whether they have decreased in recent decades.  All written material indicates the boas are common where found.

Skins of Boa nebulosa, Photo Ricky Lockett

Aside from these factors, the major risks for the species are habitat destruction and climate change.  The latter is an issue since warmer oceans lead to an intensification of hurricanes.  In 2017 hurricane Maria destroyed large parts of the island leading to 65 dead inhabitants and large areas destroyed.  While media reports covered mostly areas inhabited by humans, large parts of the island were affected by landslides as a result of the amounts of rainwater which precipitated in short time.  Therefore it is estimated that all wildlife was severely affected as a result of this hurricane.

In terms of conservation, the study of Ackley et al. brings interesting aspects to light.  They did a rapid assessment of the herpetofaunal diversity in altered habitats on Dominica. While they did not include Boa nebulosa in their study, the results are interesting for conservation.  They found the highest abundance and species richness in moderately to substantially modified areas.  They conclude that conservation efforts in the West Indies need not be restricted to pristine habitats, but also might include protection of slightly to moderately disturbed areas that may sustain even greater biodiversity .

A 2013 study conducted by the Texas A&M University to determine the number and types of ticks and their hosts was conducted on the island.  The two species of ticks found were tentatively identified as Amblyomma americanum and Amblyomma cajennense.   Captured for the study were both Boa nebulosa and Ameiva fuscata.   The reptiles were captured from  21 May, 2013 through 1 June, 2013.  Seventeen boas and thirteen lizards were captured during this period.  The author posits there is a size correlation between tick and host; the boas were infested with large adult ticks (mostly male) while the Ameiva attracted smaller ticks.  Male Amblyomma cajennense was the predominant tick of the 2  species found .

Boa nebulosa  has not been systematically studied since Lazell described it as a subspecies.  The Dominica Boa is an  excellent candidate for a genome project that includes a life cycle study.

The CIA World Factbook lists the following environmental threats for Dominica: water shortages a continuing concern; pollution from agrochemicals and from untreated sewage; forests endangered by the expansion of farming; soil erosion; pollution of the coastal zone by agricultural and industrial chemicals, and untreated sewage .

The map below illustrates the areas affected by habitat destruction and alteration due to development and agriculture.

Topographic map of Dominica
Early map of Dominica, 1776.

Deforestation, as a result of agriculture and plantations, began long before this map was drawn.  The deforestation extends halfway up the mountains in the background.  Presumably the land above the tree line was agriculturally useless.

Early map of agricultural Dominica, 1776. Note how far removed the tree line is.

 

On display in these Zoos

We are unaware of this species being currently held in any zoos or academic collections worldwide. According to the international species information system (www.isis.org) the boa was kept at the Glasgow Zoo, with one male, one female and 34 specimens of unknown sex (possibly being the result of breedings). The Glasgow Zoo closed in August 2003. We are unaware of the fate of the boas. We could not find any other listings of Boa nebulosa in any zoo. If you have further information please Contact us.

Historical note from Frederick Ober’s 1880, “Camps in the Caribbees,” while visiting Dominica in 1879:
“One day he brought to my door an iguana, nearly five feet in length, and very ugly. He had seen it  basking on a limb beneath the cliff, and had pinned it with a long bamboo, while his brother secured it with a noose made from a liane.  I expressed a desire to obtain its skin, and hastened to do so, but a woman was already scorching the scales, which she afterward scraped off in water.  It looked quite repulsive, but  a piece which they later sent me I ate, finding it sweet, tender, and white, not unlike chicken.  This is the season (March and April) when the iguana leaves the rocks and precipices, and takes to the trees.  He lives
on grass and leaves, principally, if not solely, and only frequents the trees, they say, during the dry season; then he is hunted.  During the wet season he lives in his hole, or if he comes out he is hard to find.  The dogs of Laudat are trained to hunt this lizard.”

Notorious Nebulosas

Further photographs of Boa nebulosa

Boa nebulosa Canefield, Western Dominica. Picture by Joseph Burgess

Continue to Boa orophias

 

Citations