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Emerald Tree Boa

Order: Squamata
Family: Boidae
Genus/species: Corallus caninus

The emerald tree boa has a large, bulky head that is clearly distinguished from the much thinner neck. The back of the head is defined by two fairly large bulges on either side that contribute to the bulkiness of the head. These bulges may be used as an energy reserve as emaciated individuals often lose these bulges. The bulges slope forward to a snout that is angled such that the lower jaw appears to be shorter than the upper jaw.

The eyes have pupils that are thin and vertically oriented like those of a cat. They have many heat receptors that are also present in most boids. These heat receptors pick up infrared radiation and actually gives the snake an image of the thermo-environment around them.

The stout body 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 more than two inches (5 cm) in diameter. Emerald tree boas are by far the thickest members of the Genus Corallus. Only Trinidad tree boas rival emerald tree boas in girth but they are longer and therefore appear thinner.

Emerald tree boas 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 polychromatic 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 white triangles or seesaw patterns weakly bordered with blacks, grays, 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 towards the head. 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 seven to ten feet (2 to 3 m). The Peruvian specimens seem to be second largest as far as bulk is concerned. Typically, boas attain lengths of the four to six feet (1.2 to 1.8 m).

The emerald tree boa has many unique characters that distinguish it from other snakes. Although a majority of boids have heat receptor pits, they do not have nearly the quantity that emerald tree boas possess. 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, emerald tree boas are strictly arboreal and encountering individuals on the ground usually means something is wrong.

Distribution and Habitat
The range of the emerald tree boa includes Venezuela, Colombia, Peru, Bolivia, Guyana, French Guiana, Suriname, and Brazil. As range proceeds further and further into the Amazon Basin, length and body girth seem to increase.

Emerald tree boas inhabit wet lowland rainforests. They are found in the canopy and the understory of the rainforest and are reported to be most common in branches overhanging bodies of water. Emerald tree boas are found only in areas that receive more than 59 inches (150 cm) of rain annually. The leafy-green coloration of adults gives them perfect camouflage among the leaves while the white patterns on their body resemble the occasional patches of light that penetrate the forest's dense canopy. Elevation wise, emerald tree boas are found anywhere from 0 to 3,200 feet (0 to 1,000 m).

Diet in the Wild
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.

Emerald tree boas actually feed primarily on mammalian prey--mainly arboreal rodents such as the rice rat. They can also feed on lizards, monkeys, and bats.

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, likely to take advantage of gravity.

Zoo Diet
They are fed mice, rats, and chicks.

Males mature sexually at three and four years of age while females take a year longer and mature sexually at four to five years of age. Gestation in emerald tree boas is quite long. Females are gravid for about seven months during which they seldom feed but they do bask. Emerald tree boas appear to breed every two years. The long gestation and the size and number of young tend to put females too far behind for the next breeding season. Emerald tree boas are ovoviviparous and young are born alive. Emerald tree boas can have very large clutches but eggs typically number between three and eight . Clutches consisting entirely of unfertilized ova (slugs) have been known as well as litters containing only a single young.

They can be born green, brick red, orange, yellow, or a combination of the colors. Typically, within six months to a year, the young, which are brick red or orange, will begin to change their color to the brilliant green seen in adults. This variation in coloration is referred to as juvenile polychromatism as the juveniles take on many different colors. Why juvenile emerald tree boas are polychromatic 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.

Life Span

There is no special status for the emerald tree boa.

Fun Facts
The green tree python and the emerald tree boa exhibit many similar behaviors and characteristics. This makes a great example of convergent evolution in which two unrelated species have evolved similar characters because of the similarities of their environments.

The species name, 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, are reminiscent of a dog's head when looked upon from the side. Furthermore, the elongated maxillary teeth resemble the canine teeth of dogs.