When you think of a monitor lizard, you often picture an impressive animal – a large exotic lizard, such as the Komodo dragon, which fascinates with its size and striking appearance. However, these are not suitable as pets. But there are also small monitor lizards for terrariums. One such species is the emerald tree monitor (Varanus prasinus), also known as the green tree monitor, which belongs to the subgenus Euprepiosaurus. These extraordinary animals inhabit the rainforests of New Guinea and impressively demonstrate how diverse the world of monitor lizards can be.
Many terrarium enthusiasts wonder which monitor lizard is suitable for a pet and if it’s complicated to keep one. This article is about the fascinating lifestyle of tree monitor lizards, especially the emerald tree monitor, and how to keep them in a terrarium. They are real eye-catchers and are known as the ‘jewels of the tropics’ for good reason.
Where do tree monitor lizards come from?
Tree monitor lizards such as the emerald tree monitor (Varanus prasinus) originate from the tropical rainforests of New Guinea and the surrounding islands. There, these lizards live predominantly in the treetops, where their slender build and prehensile tail make them perfectly adapted to life there. As skilled climbers, they feed on insects, small vertebrates and bird eggs in the wild. Their habitat is characterised by dense greenery, high humidity and temperatures that remain warm all year round.
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What tree monitor species are there?
The genus of tree monitor lizards is diverse and includes several fascinating species. Particularly well known are the green Varanus prasinus, the blue Varanus macraei, the yellow Varanus reisingeri and the black Varanus beccarii. Each of these lizards has its own characteristics and colour patterns, which make them sought-after animals in terrarium keeping.
- Varanus prasinus – the emerald tree monitor: also known as the green tree monitor. It lives in the rainforests of New Guinea and impresses with its bright green colouring. Varanus macraei – the blue tree monitor: This rare species originates from the island of Batanta in western New Guinea and is particularly striking due to its intense blue colouring. Varanus reisingeri – the yellow tree monitor: With its yellowish-green colouring, it stands out clearly from the other species. Terrarium owners often know it as the yellow tree monitor, and it is one of the most colourful representatives of the tree monitors. It is native to the island of Misool in western New Guinea. Varanus beccarii – the black tree monitor: This monitor lizard is almost completely black in colour and inhabits the forests of the Aru Islands. Its dark appearance makes it particularly impressive.
In addition to these species, there are other representatives such as Varanus rudicollis or various dwarf monitor lizards, such as Varanus gilleni, which are also among the popular monitor lizard species in terrarium keeping. As mentioned at the beginning, we will now focus on the green tree monitor and address frequently asked questions about keeping it in a terrarium.
Is the emerald tree monitor poisonous?
A lot of people wonder whether the emerald tree monitor is poisonous and whether it should be classified as dangerous. In fact, like other monitor lizards, it is one of the lizard species with a mildly poisonous mouth flora. This means that its saliva contains certain enzymes and bacteria that can be harmful to small prey animals. But this monitor lizard is not dangerous to humans.
Although a bite from an emerald tree monitor can be painful and cause minor swelling, there are no known cases of serious poisoning. It is much more important to handle them with care to avoid stressing the animal and to prevent injury to both humans and animals.
This means that the emerald tree monitor is not poisonous in the traditional sense and poses no danger to terrarium owners.
How big does an emerald tree monitor grow?
The question of monitor lizard size is asked particularly frequently by terrarium enthusiasts. The emerald monitor lizard (Varanus prasinus) usually reaches a total length of about 80 to 100 centimetres, more than half of which is accounted for by its long, slender tail. This tail not only helps the animals to climb, but also aids their balance in the treetops.
The actual body length without the tail is significantly shorter, usually around 30 to 40 centimetres. This makes the emerald tree monitor one of the smaller representatives of its genus, clearly distinguishing it from larger species such as the Komodo dragon.
So when looking at the size of an emerald tree monitor, bear in mind that the information always refers to the total length including the tail.
How much space does an emerald tree monitor need? How big does the terrarium need to be?
Keeping emerald tree monitors (Varanus prasinus) requires a generously sized terrarium that takes into account the lifestyle of this tree-dwelling lizard. As a predominantly climbing species, the aquarium height is really important. The terrarium for an adult emerald tree monitor needs to measure at least 150 × 80 × 150 cm (L × W × H). This size will provide sufficient space for the emerald tree monitor to engage in its natural movement and climbing habits. Larger is always better, as the animals feel much more comfortable in a spacious environment and can better display their natural behaviour.
The emerald tree monitor belongs to the group of small monitors, but even so it needs a considerable amount of space. If you want to keep several animals, you need to plan a larger terrarium for Varanus prasinus and also create plenty of hiding places and climbing opportunities. It is also advisable to set up several warm spots so that the lizards can maintain their distance from each other when basking in the sun. It is possible to keep them in pairs, provided there is sufficient space and "hidey holes”. However, keeping them in groups on a permanent basis is difficult and in many cases leads to stress or territorial disputes. If you have a group of young animals, you need to observe the group dynamics. Once they reach sexual maturity, you’ll be able to see which animals get along with each other and which do not. Now, at the latest, it’s time to act and, if necessary, to separate the monitor lizards. We at JBL run a rearing terrarium. As soon as the animals reach sexual maturity, they are moved to a larger terrarium.
Setting up the emerald tree monitor terrarium
A structurally rich environment is essential to allow the animals to follow their tree-dwelling lifestyle. All monitor lizards are diurnal reptiles. It is therefore advisable to simulate a consistent daily rhythm in the terrarium. The interplay between spotlights and hiding places is also crucial to allow them to regulate their body temperature independently.
Consider the following points when setting up your equipment:
- Sturdy climbing branches and cork tubes at different heights provide support and freedom of movement. Dense greenery with robust plants or artificial plants provides privacy and conveys a sense of security.
- Caves and hiding places (e.g. JBL ReptilCava GREY) both on the floor and in the upper areas of the terrarium serve as places to retreat to.
- A structured substrate consisting of pine bark, coconut humus, soil or bark mulch stores moisture and stabilises the climate. JBL TerraBark is a suitable substrate for rainforest terrariums.
- Several warm spots in the terrarium prevent stress, as the animals can choose where they want to sunbathe.
- Water bowls (e.g. JBL ReptilBar GREY) as a drinking source
Equipment: JBL ReptilCava GREY , JBL TerraBark , JBL ReptilBar GREY
In addition to the emerald tree monitor, other species such as Varanus macraei, Varanus reisingeri and Varanus beccarii have similar requirements in terms of space, structure and equipment.
As a general rule, a tree monitor terrarium must always be tailored to the respective species and its activity level. Although keeping tree monitors differs from keeping ground-dwelling monitors, it follows the same basic principles of species-appropriate monitor keeping
What technology does a terrarium for emerald tree monitors require?
In order for an emerald tree monitor (Varanus prasinus) to feel comfortable in its terrarium, the technology must replicate the conditions of its natural habitat as closely as possible. Temperature, lighting and humidity are crucial factors here. Good ventilation of the terrarium is also essential.
- Temperature: During the day, the terrarium needs temperature zones between 26 and 30 °C. Under the heat lamp, local sun spots may even be as warm as 35 °C. At night, the temperature may drop to around 22–24 °C. Lighting: Strong UV lighting is essential. This is the only way emerald tree monitors can produce the vitamin D3 vital for them to develop a healthy bone structure. Special metal halide lamps (L-U-W/HQI) are therefore required, as they provide a full spectrum similar to sunlight. This includes UVA and UVB radiation and heat for the terrarium. The JBL ReptilJungle L-U-W Light alu is a full-spectrum spot sun lamp made of aluminium for rainforest terrariums. However, ballasts such as the JBL TempSet Unit L-U-W are required to operate these lamps. Burn protection baskets, such as the JBL TempProtect II light, are a useful addition for this purpose. After switching off the lamp, the temperature in the terrarium decreases, which corresponds to a natural night-time temperature reduction. To simply illuminate the terrarium, we recommend LEDs such as the JBL Reptil LED Daylight 13W, which can be reinforced with reflectors (JBL TempReflect light).
- Humidity: Tree varans originate from tropical rainforests. Accordingly, the humidity in the terrarium should be between 70 and 90% during the day. Regular spraying or the use of sprinkler systems ensures that the animals can develop their typical activity. Hygrometers and thermometers (JBL TerraControl) are required to monitor humidity and temperature.
Technology: JBL ReptilJungle L-U-W Light alu (Special lamp for use in reptile keeping! Not suitable for other applications! No EEK label required. Exemption according to (EU) 2019/2015 Annex IV 3. c) UV radiation > 2mW/klm) , JBL TempSet Unit L-U-W , JBL TempProtect II light , JBL Reptil LED Daylight 13W , JBL TempReflect light , JBL TerraControl , JBL TerraSafe
Only when temperature, light and humidity are in harmony will emerald tree monitors display their full range of behaviour – from climbing to hunting. High-quality technical equipment is therefore essential for successfully keeping these animals.
What do emerald tree monitors eat?
In the wild, emerald tree monitors are skilled hunters that search mainly in treetops for their food. Their diet includes insects, spiders and occasionally eggs. They are therefore carnivorous reptiles. This varied diet ensures that they receive all the important nutrients they need in their tropical habitat.
Im Terrarium orientiert sich das Smaragdwaran Futter ebenfalls an dieser natürlichen Vielfalt. Geeignet sind in erster Linie Heuschrecken, Grillen, Schaben und andere Insekten, die regelmäßig mit Vitaminen und Kalzium angereichert werden sollten. Hierfür eignet sich zum Beispiel das JBL PROTERRA REPTILE FLUID and JBL PROTERRA CALCIUM POWDER are suitable for this purpose, for example.
It is important to provide a varied diet and to adapt it to the animals' activity levels. This will keep them healthy and active, allowing them to display their natural hunting behaviour even in the terrarium.
How old do emerald tree monitors become?
The emerald tree monitor's age is another important issue. In the wild, the animals usually reach an age of about 10 to 12 years, although factors such as food supply, climate and predators have a major influence.
Under optimal terrarium conditions, however, the emerald tree monitor's life expectancy can be significantly higher. With species-appropriate care, a balanced diet and the right technology in the terrarium, some animals can reach an age of up to 15 years or more.
The life expectancy of Varanus prasinus depends heavily on how well the living conditions reflect their natural habitat. By ensuring suitable temperatures, high humidity, varied food and places to retreat, you can create the best conditions for these fascinating lizards to live a long and healthy life.
Determining the sex of the emerald tree monitor
Distinguishing between the sexes in tree monitors is a challenge for many keepers, as the differences between males and females are difficult to see externally. Even in the emerald tree monitor (Varanus prasinus), the indications are very subtle.
- Males often have a slightly more powerful head and appear more massive and slightly larger overall. In adult animals, it is sometimes possible to see the so-called hemipenis pockets (thickening at the base of the tail), which indicate that the animal is male.
- Females, on the other hand, usually appear slimmer and have a more uniform body shape.
However, a visual inspection alone is rarely sufficient to determine the sex of Varanus prasinus. It is particularly difficult to determine the sex of young animals with certainty. In practice, many breeders therefore resort to methods such as probing, endoscopy or even DNA analysis to obtain certainty.
For private ownership, accurate sex determination is only important if breeding is desired or if the animals are to be kept in pairs.
Reproduction of emerald tree monitors
The reproduction of monitor lizards is complex and poses challenges even for experienced keepers. In the case of the emerald tree monitor (Varanus prasinus), the mating season usually begins with a rise in temperature and increased humidity, which mimics the natural rainy seasons in New Guinea.
During mating, the male displays active courtship behaviour and tries to hold the female in place by biting her neck and moving his body. After successful mating, the female lays several eggs in prepared nesting sites or in soil that can be dug into. Depending on temperature and humidity, the incubation period is usually 150 to 180 days.
Breeding emerald tree monitors is considered challenging, as the right balance of climate, space and nutrition is crucial. Many emerald tree monitor breeders therefore work in precisely controlled conditions in order to obtain healthy offspring.
Other species such as Varanus macraei and Varanus reisingeri can also be bred successfully. However, tree monitor breeding is generally complex, as the animals are sensitive to any errors in their keeping conditions. Anyone interested in breeding Varanus prasinus should therefore read up extensively on the subject or seek advice from experienced keepers and breeders.
Conclusion: Are emerald monitors suitable for beginners?
Emerald tree monitors are undoubtedly among the most fascinating representatives of tree monitors with their striking green colouring, their impressive climbing skills and their lively behaviour. At the same time, our outline has shown that keeping emerald tree monitors involves highly demanding quantities of space, technology and experience. Anyone wanting to keep this species needs an in-depth knowledge of terrarium keeping and should be prepared to invest a lot of time and care in their maintenance.
All in all, the emerald tree monitor is a real highlight for experienced terrarium owners, but not a classic beginner's monitor. If you are just getting started in the world of monitors, consider familiarising yourself with simpler species first – and only devote yourself to the ‘jewels of the tropics’ once you have mastered the basics of terrarium keeping.
If you have any questions about ‘tree monitors in terrariums, please feel free to write them in the comments!
