The emerald tree boa has many unique characters that set it off from other snakes. Although a majority of boids have heat receptor pits, they do not have nearly the quantity that emerald tree boas possess. These heat receptors enable emerald tree boas to target any animal giving off infrared radiation. The characteristic coil of emerald tree boas is very conspicuous and is only replicated by the green tree python of Australia and New Guinea. They sit draped over a single branch with their body coiled such that their head rests more or less right in the center. Unlike their Corallus relatives who will spend time on the ground, emerald tree boas are strictly arboreal and encountering individuals on the ground usually means something is wrong.
Since the late 1980's and early 1990's, there has been a significant increase in the interest of maintaining emerald tree boas in captivity in the private sector. However, many animals are wild caught individuals which have been tremendously traumatized through the importation process and don't survive long in captivity. The good news is that increased success of private herpetoculturists in breeding emerald tree boas as well as several nations restricting the exportation of emerald tree boas from their lands will help decrease the number of animals imported each year. Furthermore, more is being learned about these fascinating snakes and attempts to adjust individuals to captivity are more and more successful as time goes on.

© 1998 - 2002 Paul Huang unless otherwise noted

enlarged teeth of the emerald tree boa contribute to its dog-like qualities

The name given to the Genus originates from Daudin's initial observation of the Amazon tree boa. Daudin named the Genus such because the pattern and colors of the garden color phase of the Amazon tree boa is coral-like, hence Corallus.

Caninus comes from the emerald tree boa's resemblance to dogs. The posterior bulges on the head of the emerald tree boa, along with the angled snout, is reminiscent of a dog's head when looked upon from the side. One needs to open the mouth of an emerald tree boa to see the sets of enlarged teeth located on the front of the maxillary bone. These enlongated 'canines' in the front of the mouth also make the emerald tree boa similar to dogs.

While other species in the genus are part of a certain complex, the emerald tree boa has not had any subspecific status designated to its different types. Emerald tree boa classification is fairly straight forward. It is placed within the Boine subfamily that divides the boas from the pythons. From there, the Genus Corallus is nested between the Indonesian boas and New World & Madagascan boas1. Within the tree boas, the emerald tree boa is believed to be the second most ancestral of the tree boas. It, along with the Cropan's boa, is the closest representative to the common ancestor of the tree boas.

Kingdom: Animalia Superfamily: Henophidia
Phylum: Chordata Family: Boidae
Subphylum: Vertebrata Subfamily: Boinae
Class: Reptilia Genus: Corallus
Order: Squamata species: caninus
Suborder: Serpentes
It is likely that subspecific status is in need with emerald tree boas because distinctions in morphology and scalation appear present between certain populations such as: the Amazon River basin, Peru/Ecuador, and Guyana & Suriname.

Emerald tree boas are fortunate to have only a few common names. It is mostly referred to as the emerald or green tree boa. They are referred to as Yea-tah-yah-mo by the Akawai Indians of Guyana2. Below is a list of common names found in other languages.

Dutch: gröen boom boa, grüner hundskopfschlinger, echte hundskopfboa
English: dog boa, emerald boa, emerald tree boa, green tree boa, parrot snake, yellow-faced boa
German: grüne hundskopfboa, hundskopfboa
Portuguese: jibóia-verde
Spanish: boa esmeralda, boa verde, cobra papagio, cobra verde, falsa mapanare verde
Swedish: grön träd boan, smaragdboa

The emerald tree boa has a large, bulky head that is clearly distinguished from the much thinner neck. Posteriorly, the head is defined by two fairly large bulges on either side that contribute to the thickness of the head. These bulges are postulated to be somewhat of an energy reserve as emaciated individuals often lose these bulges. These bulges slope forward to a snout that is angled such that the lower jaw appears to be shorter than the upper jaw. Viewed from above, the head of the emerald tree boa has a thin snout that widens into the cranium. The eyes are set just before this widening. The pupils are thin and vertically oriented like a cat. Both the supralabial and infralabial scales are pitted and encase the many heat receptors that are present in most boids. These heat receptors pick up infrared radiation and actually gives the snake an image of the thermo-environment around them. A blackish-blue mark is present on the underside of the head that is greater than 3 cm long and visible when prey is being swallowed3. This colored mark defines the deep subgular "fold" located in the bottom of the mouth.

A thin neck follows the large head clearly setting the head off from the body. The stout body follows and is laterally compressed. It ends with a strong prehensile tail that allows the emerald tree boa to anchor itself to the branches on which it coils. The body is thick and can be over 2 inches in diameter. Emerald tree boas are by far the thickest members of the Corallus. Only Trinidad tree boas rival the emerald tree boa in girth but they are longer and thus thinner in appearance.

Emerald tree boas can vary greatly in body color as well as pattern shape and pattern color. Typically, adults vary in shades of green as a background color while juveniles are polymorphic and can be quite variable. There are natural trends seen in individuals from certain locales however. Ventrally, the emerald tree boa varies from creamy white to bright, sulfur yellow. Dorsally, the emerald tree boa has enamel white triangles or seesaw patterns weakly bordered with blacks, grays, and/or dark greens. The triangles are arranged in such a manner that the base of the triangle lies along the backbone. These markings are often gray and not as sharp anteriorly. As the blotches progress posteriorly along the snake, they become white and well defined. In some individuals, the blotches remain gray throughout the body.

Sizes, like patterns vary with locality. Amazon River Basin specimens are the largest attaining lengths between 7 - 9 feet in length with reported lengths of 10 feet as well. The Peruvian specimens seem to be second largest as far as bulk is concerned. They typically attain the longer lengths of the 4 - 6 feet that are reported for the other localities of emerald tree boas. The largest size for emerald tree boas reported by Henderson4. was 1.34 meters (4 feet 4¾ inches) snout-to-vent.

AMAZON BASIN: Amazon basin emeralds, unlike Guyana shield emeralds, often have a yellow or sulfur yellow belly color. The body color of Amazon basin animals is darker green generally and is marked with a white, dorsal stripe. Enamel white triangles protrude out from this stripe and move down the sides of the body towards the belly. The stripe is often bordered by some degree of black. The anterior head is comprised of proportionally smaller scales than Guyana shield specimens5. Size-wise, Amazon Basin animals are the largest.

ECUADOR: Ecuadorian emerald tree boas rarely have been seen by anybody outside of Ecuador. Individuals are likely an intermediate between Guyana shield and Peruvian specimens. One characteristic of Ecuadorian emerald tree boas is the presence of numerous conspicuous white blotches running all along both sides with blotches occasionally touching the belly's white coloration.

AMAZON BASIN
Maddelena Guidi ECUADOR
Robert Henderson NORTHERN
David L. Hinojosa PERU

GUYANA SHIELD, NORTHERN, SURINAME: Guyana shield animals are the most common "type" of emerald tree boas seen in captivity. Specimens are typically a rich but lighter shade of green. The scales of the snout are large. The patterning of Guyana shield specimens is a typical seesaw pattern. These blotches are most commonly enamel white often originating as gray or mottled gray anteriorly. The gray blotches develop into the bright white as it proceeds posteriorly. Bluish gray or black scales border these blotches inconsistently. The belly is white or creamy white in color. Individuals from Suriname differ slightly in that they typically have higher contrasting patterns. Specimens showing a complete lack of patterns or a tremendous reduction of patterns (only a few blotches of white) have been found in populations within the Guyana Shield range and it is likely this is a naturally occurring phenotype within the Guyana shield population. The patternless trait has been proven to be genetic by John Hedger. Most Guyana shield specimens attain lengths between 4 - 6 feet as adults.

PERU: The Peruvian emerald tree boa is similar to the Amazon Basin in size although it is a bit smaller. Individuals possess a dark green color patterned by highly contrasting white. The white blotches are triangular in shape but begin in more of a bulb shape (tear-drop pattern) near the backbone versus a triangular shape. The anterior head scalation in Peruvian emerald tree boas is also an intermediate between the Amazon Basin and Guyana shield types.

As with all boids, emerald tree boas have spurs (anal claws) located along either side of the cloaca. Not too much of a significant size difference in the spurs of males and females is present. Therefore, it is difficult to sex specimens based on their spur length.

With the increasing interest in the private sector in emerald tree boas, more and more color patterns and possible mutations are showing up. The viabilities of many of these lines are still questionable but it is likely these variations are here to stay. A rumor of an albino emerald tree boa has yet been truly verified with the presence of pictures as far as the author knows.

Calico: a most interesting animal, the calico emerald is adorned with blotches of greens, whites and yellows in random spots. Unfortunately, the lone specimen - from an European collection in the 1980's - has since died.

calico patterned emerald tree boa

Classic Basin: the classic basin emerald tree boa resembles the typical Amazon basin emerald tree boa with a complete or almost complete stripe and triangles coming from the stripe.

Dark Phase Suriname: dark phase Suriname emerald tree boas have a broad and dark border around the white blotches along the body. They have an overall darker appearance and the trait seems to be breeding true to an extent6.

Granite: named after their unique appearance7, granite emerald tree boas show an interesting color pattern similar to some of the Biak type green tree pythons. Individuals have varying amounts of yellow speckled onto the green body.

Increased Melanin: the increased melanin emerald tree boa has an increased amount of darker green or black coloration that is found in spots other than bordering the white blotches such as on the head.

Light Phase Suriname: in contrast to the dark phase Suriname emeralds, light phase emeralds lack the border which surrounds the white blotches and thus appear much lighter. This line also appears to breed true6.

Melanistic: the melanistic emerald is unlike any other emerald. Although there is still green, melanistic individuals have an extraordinary amount of black, probably between 60 - 90%. The coloration of the scales is actually black and not a dark green or blue6.

New Locality: new locality animals are somewhat of a cross between Amazon basin and northern individuals. Animals possess teardrop-shaped blotches dorsally, have dorsal-ventrally elongated blotches laterally and eyespots scattered throughout.

Patternless: patternless individuals are quite common in emerald tree boas and specimens from the Guyana shield and Amazon basin areas are known. Patternless individuals are not sometimes completely patternless but occasionally have only a few blotches. The patterning is tremendously reduced.

Snowflake Basin: snowflake basin emerald tree boas are "characterized by copious amounts of white overflowing the dorsal line with good sized diamonds"8. They have a broad stripe with large triangular blotches.

Star Basin: a most conspicuous patterned type, the star basin emerald has a very broken dorsal stripe. However, the placing of the breaks is such that the striping is present where it meets the triangles. This gives the animal the appearance of numerous stars along the dorsal midline.

Wide Stripe Basin: the wide striped basins are similar to the classic basins in terms of patterns except that the dorsal stripe is much wider being more than a few scales wide.

Species are defined by using a set of characters that sets each species apart from another. One of the groups of characters used by herpetologists is scale counts. By using the number of scales a snake has in certain areas, they can diagnose species. Of course, since every individual is different, a range of scale numbers is given per character for any given species. Here is a list of scale count values for emerald tree boas compiled from Stafford and Henderson2 as well as Boulenger9.

The loreals number between 2 - 5 with the latter scales occasionally fused. There are 2 - 10 subloreal scales underlying the loreals. Supralabials number 9 - 13 and all are equipped with pits with exception of the last scale. Between 11 - 16 infralabial scales line the lower lip with the first and last scales not pitted. One or two preoculars are located anterior to the eye, which is surrounded by 9 - 19 circumorbital scales. There are between 4 - 15 scales between the supraorbitals.

The maximum number of dorsal scale rows at midbody is 84. The number of ventral scales vary between 186 - 219 and they terminate in a single, undivided anal plate.

Many neonate emerald tree boas are not green but red, orange or one of these colors and green. Green neonate emerald tree boas are actually rare, at least in captive collections. Red and orange individuals are the most common and are the most prominent in most litters. This variation in coloration is referred to as juvenile polymorphism as the juveniles take on many different colors. Why juvenile emerald tree boas are polymorphic is still a question. It is hypothesized that they mimic the arboreal, multi-colored vipers of Central and South America. As they mature, they turn to camouflage instead of mimicry.

Three differently colored neonates.
Schulte3 described the color change process as follows: White dorsal markings are only present in the posterior region of the neonates. First, the small green blotches located laterally increase in size and number. Only when these green blotches appear do the white dorsal markings begin to appear anteriorly. Next, the head changes from orange or red into an orange-green color and then the process continues for the rest of the body. A shed occurs and almost all of the orange/red tones disappear. The process took three juveniles he possessed 6 - 8 weeks, 10 - 14 weeks, and 17 - 20 weeks. Generally, the neonatal color change begins within the first 6 to 12 months. At this age, emeralds are near the two-foot mark or more in length. Of course this varies from individual to individual depending on factors such as feeding frequency, prey size, genetics, etc. The author knows of no emeralds not having undergone this color change.

Being strictly arboreal and feeding relatively infrequently does not help speed up the growth rates of emerald tree boas. In fact, emerald tree boas tend to take one or two years longer to reach sexual maturity than the typical boid.

Only one natural predator of emerald tree boas has been identified in literature. It is the Guianan Crested Eagle (Morphnus guianensis)10. The ecology and predator/prey relationships involving emerald tree boas still need to be extensively studied. Schulte3 believed that emerald tree boas in Peru were often killed by humans because of fear created by the presence of Bothriopsis bilineata smaragdinus (palm viper) in the same region. Externally, they are somewhat similar in appearance.

Emerald tree boas were traditionally thought to feed exclusively on birds. They have been known to grab birds that are in mid-flight. The long, curved, and extremely sharp teeth of the maxillary and rostrum are used to penetrate the feathers and hold-on to them before the snake throws its coils around the prey.

But most of the data suggests this is not the case. It shows emerald tree boas feeding primarily on mammals. Other physical characteristics of emerald tree boas suggest this as well. This idea is supported by the presence of the heat receptors located on the labials of the emerald tree boa. Heat receptors would seem to be rather ineffective in detecting flying and even nested avian prey. Although birds are endothermic, they give off relatively less body heat than mammals. These pits could be used for better detection of endothermic prey. Robert Henderson12 looked at the stomach contents of 11 emerald tree boas. Of the 11 items, 10 were rodents being primarily the rice rat (an arboreal rodent). The other was a skink (possibly Thecadactylus rapicauda) found in the smallest of the emerald tree boas2. Other authors have listed the natural diets of emerald tree boas to include: monkies, squirrels, rats, birds and bats3.

The long and sharp teeth are probably used not to penetrate bird feathers but to hold onto their prey because if the prey escapes, they fall to the forest floor and energy spent in procuring the prey would have been wasted11. Support for this idea is found in a paper published by Deufel and Cundall examining the angle between the tip of the first 4 maxillary (front) teeth and the maxilla bone. Corallus have the smallest angle of several boid species examined13. This means that their tooth tips are pointed posteriorly more than the other species. Deufel and Cundall suggest there is a racheting action when a boid strikes the prey. The teeth glide over the prey and only penetrate them when the prey recoils or reacts to it. So instead of stabbing their prey, these teeth are used to hold onto prey. This supports the "meathook" idea where they are used to hold onto prey11.

Constriction is usually accomplished with one or two coils of the anterior body while the posterior half of the body, along with the prehensile tail, is used to anchor the snake to the branch. Swallowing of prey is for the most part done going upwards with one coil around the prey to likely take advantage of gravity.

1 Kluge 1991 6 Nicoli pers. comm. 10 Greene 1997
2 Stafford & Henderson 1996 . 11 Henderson pers. comm.
3 Schulte 1988 8 Chiras 2000 (web) 12 Henderson 1993c
4 Henderson et al. 1995 9 Boulenger 1961 13 Deufel and Cundall 1999
5 Chiras 1998

© 1998 - 2002 Paul Huang unless otherwise noted