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Morelia viridisGreen tree python

By Michael Hillman

Geographic Range

Green tree pythons (Morelia viridis) are found only within the Australian region. These pythons are found throughout New Guinea and surrounding islands with the exception of the Bismarck Archipelago. They also occur in the Cape York Peninsula of Queensland, Australia. The juvenile yellow morph of Morelia viridis is found throughout this range, while the juvenile red morph is only found in parts of New Guinea. (Rawlings and Donnellan, 2003; Wilson and Heinsohn, 2007; Wilson, et al., 2007)

Habitat

Morelia viridis is a tropical rainforest species inhabiting mainly low montane and lowland rainforest habitat ranging from 0 to 2000 m. They may also be found in secondary forests and areas of re-growth. When young, green tree pythons restrict themselves to canopy gaps or along the edges of forest where light can easily reach the ground. As adults, they are generally found in closed-canopy rainforests. (Rawlings and Donnellan, 2003; Wilson, et al., 2006a; Wilson, et al., 2006b)

  • Range elevation
    0 to 2000 m
    0.00 to 6561.68 ft

Physical Description

Morelia viridis reaches an average length of 1.5 meters; with the largest recorded specimen being 2.2 meters in length. The head scales are irregular and small and their labial heat-sensing pits are only found within the scales on the upper lip. Their tail is prehensile, helping them to climb. Green tree pythons do not appear to exhibit sexual dimorphism in adulthood; however, at smaller lengths juvenile females have both wider and longer heads when compared to males of similar size. (Bartlett, 1995; Torr, 2000; Wilson, et al., 2006b)

As adults, green tree pythons display a brilliant green over most of their bodies. On the dorsal surface there us a distinct ridge of scales that is usually white to yellow in coloration and forms a broken or continuous line down the length of the body. Ventrally, the scales are generally yellow. However, some individuals may have ventral scales of a more dull yellow to white and have a blue tinge scattered on the scales of the dorsal surface. (Bartlett, 1995; Torr, 2000)

Juvenile green tree pythons may be either bright yellow or brick-red. Along the dorsal surface, they exhibit a series of white blotches edged in black or brown. These blotches may be either symmetrical or randomly placed on both sides of the body. In both color morphs, a white streak edged in black runs from the nostril through the eye and to the back of the head. The distributions of these two color morphs seem to be different, although it is not uncommon for both color morphs to be in the same clutch in captive situations. In the wild, only the yellow morph has been recorded in Australia. Although poorly studied, the red morph seems to be restricted to the island of Biak and the Baliem Valley in Papua, Indonesia and in the Sepik basin of Papua New Guinea. In some populations of Morelia viridis, the adults may not completely change to green and will maintain some of their juvenile yellow coloration. (McDowell, 1975; Torr, 2000; Wilson, 2007; Wilson, et al., 2007; Wilson, et al., 2006b)

  • Sexual Dimorphism
  • sexes alike
  • Range length
    2.2 (high) mm
    0.09 (high) in
  • Average length
    1.5 mm
    0.06 in

Development

Green tree pythons are about 30.5 cm in length when they hatch. At this stage, they are either bright yellow or brick-red. They must undergo ontogenetic color change in order to acquire their adult green coloration. This generally occurs between six months and a year of age, but does not coincide with sexual maturity, as might be expected. Instead, at this age, the juvenile python will be between 53 and 59 cm in length and is large enough to change its foraging behavior and habitat. Each color stage appears to provide camouflage suitable to its immediate habitat. As a young snake, the red or yellow color blends in better in forest gaps or edges, where smaller animals reside. Adult green coloration blends in best in the closed canopy of the rainforest, where larger prey live. The change does not generally associate with a shedding event and may happen as quickly as overnight or take as long as several months. Red individuals of Morelia viridis take longer to undergo this change as they first lighten to a yellow color, several patches at a time, and then subsequently change to their adult green color. (Bartlett, 1995; Ross and Marzec, 1990; Torr, 2000; Wilson, et al., 2007; Wilson, et al., 2006b)

Reproduction

Reproduction in the wild has never been reported for Morelia viridis and the mating system is unknown. (Ross and Marzec, 1990; Wilson, 2007)

A majority of available information on reproduction has been published from hobbyists in the captive pet trade, though some speculation can be made from scientific research in situ. The lack of sexual dimorphism and the presence of an equal sex-ratio in green tree pythons suggests that males do not compete physically in male-male combat in order to mate with females. Instead, a male’s ability to obtain a mate may be primarily determined by how well they can search out a female. This is apparently why males do not maintain stable home ranges. Males appear to stop feeding when searching for a mate. Once the male has found a sexually mature female he will stimulate her with his cloacal spurs (vestigial digits) to make her receptive for mating. (Ross and Marzec, 1990; Torr, 2000; Wilson, et al., 2006a; Wilson, et al., 2006b)

Green tree pythons have a highly seasonal breeding cycle; however, few offspring are encountered in any one year suggesting that these pythons do not breed every year. The actual mating season in the wild is not known, though in captivity it can range widely from August to January and tends to be stimulated by the onset of low pressure fronts and storms. As is true for all pythons, Morelia viridis is oviparous. In the wild, females lay their clutches in October and then brood them for approximately 50 days, but this can range from 39 to 60 days. Hatching takes place in November, corresponding to the start of the wet season in the Australian region. At hatching, green tree pythons are approximately 30.5 cm in length and can be either brick-red or bright yellow. Reaching sexual maturity can take several years and can be long after they have changed into their adult green coloration. In males, sexual maturity reportedly occurs after 2.4 years and in females, sexual maturity occurs after 3.6 years. (Bartlett, 1995; O'Shea, 2007; Ross and Marzec, 1990; Wilson, et al., 2006b)

  • Breeding interval
    Green tree pythons have a highly seasonal breeding cycle; however, few offspring are encountered in any one year suggesting that these pythons do not breed every year.
  • Breeding season
    Mating has not been recorded for green tree pythons in the wild. It can be inferred that egg laying occurs in October, as hatching takes place in November.
  • Range number of offspring
    6 to 32
  • Range gestation period
    39 to 65 days
  • Average gestation period
    50 days
  • Average age at sexual or reproductive maturity (female)
    3.6 years
  • Average age at sexual or reproductive maturity (male)
    2.4 years

Green tree pythons exhibit some maternal care by brooding their eggs before they hatch. In captivity, females have been observed coiling around their clutches. They will often shiver and contract their coils, apparently to produce metabolic heat and thus maintain an ideal brooding temperature, which ranges from 84 to 88 degrees Fahrenheit. Once the young hatch, however, there does not appear to be any parental care. (Ross and Marzec, 1990; Torr, 2000)

  • Parental Investment
  • pre-fertilization
    • provisioning
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

Information on actual ages in the wild is limited for Morelia viridis. However, a population at Iron Range on Cape York Peninsula, Australia had an average age of 3.4 years. It is predicted that these pythons could live for at least 15 years, with a maximum age of 19. Green tree pythons in captivity have lived only slightly longer with the record age set at 20 years old. (Wilson and Heinsohn, 2007; Wilson, et al., 2006b)

  • Range lifespan
    Status: wild
    12 (high) years
  • Average lifespan
    Status: wild
    3.4 years
  • Range lifespan
    Status: captivity
    20 (high) years
  • Typical lifespan
    Status: wild
    15 to 19 years
  • Average lifespan
    Status: captivity
    20.6 years
    AnAge

Behavior

Morelia viridis is the most arboreal python species, though it may be found on the ground occasionally. As adults, they are nocturnal and hunt primarily at night when larger nocturnal prey are active as well. Before ontogenetic color change, green tree pythons are diurnal, coinciding with smaller prey that are active during the day. (Wilson, et al., 2006b)

Green tree pythons exhibit two different postures depending on whether they are resting or hunting. In a resting posture, the snake’s body is coiled up and hanging on a horizontal branch or vine. This is how the animal is generally depicted in photographs. When resting, green tree pythons often take shelter in tree hollows or epiphytic vegetation. In a hunting posture, the anterior end of the body is extended from the branch and folded like an accordion, ready to strike at the ground or at a lower branch, while the posterior end is wrapped securely around its perch. Green tree pythons typically change between these postures only during dusk or dawn to avoid giving away their location. (Cogger, 1983; Torr, 2000; Wilson, 2007)

Activity rates are different between the sexes. Females are more likely to change their position from day to day than are males. They are also more active and move further in the month of February. In contrast, males are more active in January and March. However, from about April until the start of the next breeding season in October, both sexes are sedentary and inactive. When moving, distances traveled by adult snakes are equal to the distances traveled by juveniles, regardless of their comparatively smaller size. (Wilson, et al., 2006a; Wilson, et al., 2006b)

  • Average territory size
    62100 m^2

Home Range

Only female green tree pythons have distinct home ranges. Though it varies by the length of the snake, the average size of this range is 6.21 hectares. Neither adult males nor juveniles have distinct home ranges; males adopt a mate-searching strategy, while juveniles presumably disperse from the nest. Females are not territorial as they may share a large portion of their home range with other females as well as with roaming males and juveniles. (Wilson, et al., 2006a; Wilson, et al., 2006b)

Communication and Perception

Green tree pythons are solitary snakes, so the majority of communication is interspecific. They use their labial pits as well as sight when searching for prey. Labial pits allow for infrared imaging, which is particularly important given their nocturnal habits as adults. Labial pits may also serve to help these snakes find suitable ambush and thermoregulation sites as well as help them avoid possible predators. When finding potential mates, green tree pythons most likely use chemical pheromones as opposed to visual cues. (Wilson, 2006; Wilson, 2007; Wilson, et al., 2006b)

Food Habits

As with all other snake species, Morelia viridis is exclusively carnivorous. They are obligate ambush predators feeding on small reptiles, invertebrates, mammals, and birds throughout their lives. There is a distinct change in their feeding habits that coincides with the color change from red or yellow into their adult green coloration. Once they hatch out of the egg, their main prey consists of Carlia longipes and diurnal invertebrates. In captivity, however, hatchlings have been known to cannibalize nest mates. Juvenile green tree pythons eat mostly small animals, such as lizards. As they grow in size, their gape gets larger and they are subsequently able to ingest larger vertebrate prey. In adulthood, green tree pythons eat mainly mammals and birds. For example, the main prey species for populations in the Iron Range of Cape York Peninsula, Australia are the rodents Rattus leucopus and Melomys capensis. Since they are ambush predators, green tree pythons do not move often and may use the same ambush site for up to 14 days, waiting for actively foraging prey to come within range. Caudal luring has been observed, especially in juveniles, where the tip of the tail is used to attract small animals. While an ambush feeding strategy does not yield prey often, green tree pythons have efficient digestive systems and do not require frequent feeding. (Cogger, 1983; O'Shea, 2007; Ross and Marzec, 1990; Torr, 2000; Wilson, 2007; Wilson, et al., 2007; Wilson, et al., 2006a; Wilson, et al., 2006b)

  • Primary Diet
  • carnivore
    • eats terrestrial vertebrates
  • Animal Foods
  • birds
  • mammals
  • reptiles
  • insects

Predation

The main predators of green tree pythons are rufous owls, black butcherbirds, and an assortment of diurnal raptors. Other predators include mangrove monitors, dingoes, and New Guinea quolls. (Wilson, 2006; Wilson, 2007; Wilson, et al., 2007)

The main anti-predator strategy of Morelia viridis is to avoid predation using its cryptic coloration and hiding behavior, which is especially effective against its visually-oriented avian predators. As juveniles, the yellow coloration blends in well in the rainforest edges where they are found. In juveniles with brick-red color, their coloration camouflages them better than yellow morphs against non-leafy backgrounds. It should be noted that in other species, red and yellow are typical warning colors to predators, however, green tree pythons do not appear to have any chemical defenses nor is there a dangerous model that they would be mimicking. As adults, green tree pythons inhabit the canopy of the forest and their brilliant green coloration blends in much better than either red or yellow. This suggests an adaptive basis for ontogenetic color change in this species. (Wilson, 2006; Wilson, et al., 2007; Wilson, et al., 2006b)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

As predators, green tree pythons help to reduce populations of several prey species of rodents, birds, and lizards. They also serve as food for several avian and terrestrial predators. (Wilson, 2006)

Economic Importance for Humans: Positive

The bright red or yellow coloration of green tree pythons as juveniles and brilliant green coloration as adults has made them one of the most popular species of snake kept in the pet industry today. For this reason, Indonesia captively breeds Morelia viridis for export into the captive pet trade each year. However, even with captive breeding, wild populations are still under strain because a small number of snakes are captured illegally each year and entered into the trade. Green tree pythons are also hunted by the indigenous peoples of New Guinea for food. (Wilson, et al., 2006b)

Economic Importance for Humans: Negative

As with most animals, green tree pythons may bite in self-defense. However, there are no known adverse effects of this species on humans. (Bartlett, 1995)

Conservation Status

The status of the Morelia viridis is undetermined as it is not listed on the IUCN Red List or CITES. However, populations may be vulnerable to harvest for the captive pet trade. A majority of the pet trade for the United States and Europe is supplied by populations in Irian Jaya, although there has been recent success in breeding individuals in captivity. In Australia, it is illegal to collect green tree pythons or import individuals that originated in New Guinea. Aside from the pet trade, these pythons are also vulnerable to habitat degradation through logging and slash and burn agriculture. Nevertheless, until their numbers can be accurately counted, it may be impossible to determine the status of this species in the wild. (Bartlett, 1995; Rawlings and Donnellan, 2003; Wilson, et al., 2006b)

Other Comments

Green tree pythons were once known by the name Chondropython viridis and was placed in its own genus. When scientists noticed the similarities with Australian and New Guinea carpet pythons, it was placed in the genus Morelia and given the scientific name Morelia viridis. In the pet trade, however, green tree pythons still go by the nickname “chondro” and this is unlikely to change soon. (Bartlett, 1995; Ross and Marzec, 1990)

There can be considerable variation in color and patterning in green tree pythons. Because of this, some herpetologists and many hobbyists in the pet trade separate the species into variants or races. These include the Aru, Sorong, Biak, and Yapen. While these races aren’t recognized currently, additional research may suggest these variations warrant subspecies or species status. (O'Shea, 2007)

Green tree pythons are often mentioned in discussions of convergent evolution in reptiles. This is because Morelia viridis shares similar ecology and morphology with emerald tree boas, despite their relatively distant common ancestry. Both species live in tropical rain forest habitats and are arboreal ambush predators. They exhibit similar diets and switch from a diurnal lifestyle as juveniles to a nocturnal lifestyle as adults. Green tree pythons and emerald tree boas also share the same resting and hunting postures and, remarkably, both species undergo ontogenetic color change from a red or yellow juvenile to a bright green adult. This can make it quite difficult to differentiate between the two species. One of the few ways to tell them apart is the position of the labial pits. In emerald tree boas, the pits are on the upper and lower lip. Green tree pythons only have labial pits on the upper lip surface. Emerald tree boas are found in the tropical rainforests of South America. (Bartlett, 1995; Torr, 2000; Wilson and Heinsohn, 2007; Wilson, et al., 2006b)

Contributors

Michael Hillman (author), Michigan State University, James Harding (editor, instructor), Michigan State University, Tanya Dewey (editor), Animal Diversity Web.

Glossary

Australian

Living in Australia, New Zealand, Tasmania, New Guinea and associated islands.

World Map

arboreal

Referring to an animal that lives in trees; tree-climbing.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

diurnal
  1. active during the day, 2. lasting for one day.
food

A substance that provides both nutrients and energy to a living thing.

heterothermic

having a body temperature that fluctuates with that of the immediate environment; having no mechanism or a poorly developed mechanism for regulating internal body temperature.

infrared/heat

(as keyword in perception channel section) This animal has a special ability to detect heat from other organisms in its environment.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

oviparous

reproduction in which eggs are released by the female; development of offspring occurs outside the mother's body.

pet trade

the business of buying and selling animals for people to keep in their homes as pets.

pheromones

chemicals released into air or water that are detected by and responded to by other animals of the same species

rainforest

rainforests, both temperate and tropical, are dominated by trees often forming a closed canopy with little light reaching the ground. Epiphytes and climbing plants are also abundant. Precipitation is typically not limiting, but may be somewhat seasonal.

seasonal breeding

breeding is confined to a particular season

sedentary

remains in the same area

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

tropical

the region of the earth that surrounds the equator, from 23.5 degrees north to 23.5 degrees south.

vibrations

movements of a hard surface that are produced by animals as signals to others

visual

uses sight to communicate

References

Bartlett, R. 1995. Popular Pythons and Boas: Complete guide for owners of larger snake species. Mission Viejo, California: Bowtie Press.

Cogger, H. 1983. Reptiles and Amphibians of Australia. Sanibel, Florida: Ralph Curtis Books.

McDowell, S. 1975. A Catalogue of the Snakes of New Guinea and the Solomons, with Special Reference to Those in the Bernice P. Bishop Museum. Part II. Anilioidea and Pythoninae. Journal of Herpetology, 9/1: 1-79.

O'Shea, M. 2007. Boas and Pythons of the World. Princeton, New Jersey: Princeton University Press.

Rawlings, L., S. Donnellan. 2003. Phylogeographic analysis of the green python, Morelia viridis, reveals cryptic diversity. Molecular Phylogenetics and Evolution, 27: 36-44.

Ross, R., G. Marzec. 1990. The Reproductive Husbandry of Pythons and Boas. Des Moines, Iowa: Garner Printing, Inc..

Torr, G. 2000. Pythons of Australia: A Natural History. Malabar, Florida: Krieger Publishing Company.

Wilson, D. 2007. Foraging ecology and diet of an ambush predator: the green python Morelia viridis. Pp. 141-150 in R Henderson, R Powell, eds. Biology of the Boas and Pythons. Eagle Mountain, Utah: Eagle Mountain Publishing.

Wilson, D. 2006. On green tree pythons: The ecology and conservation of Morelia viridis - PhD Thesis. Austrailian National University, 1: 1-127.

Wilson, D., R. Heinsohn. 2007. Geographic range, population structure and conservation status of the green python (Morelia viridis), a popular snake in the captive pet trade. Australian Journal of Zoology, 55: 147-154.

Wilson, D., R. Heinsohn, J. Endler. 2007. The adaptive significance of ontogenetic colour change in a tropical python. Biology Letters, 3: 40-43.

Wilson, D., R. Heinsohn, S. Legge. 2006. Age- and sex-related differences in the spatial ecology of a dichromatic tropical python (Morelia viridis). Australian Ecology, 31: 577-587.

Wilson, D., R. Heinsohn, J. Wood. 2006. Life-history traits and ontogenetic colour change in an arboreal tropical python, Morelia viridis. Journal of Zoology, 270: 399–407.

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