General information
Varanus macraei (blue treemonitor) lives on the Indonesian island Batanta. Varanus macraei is one of the subspecies in the Varanus prasinus-complex, other treemonitors in the complex are: Varanus prasinus, Varanus kordensis, Varanus reisingeri, Varanus beccari and Varanus boehmei. Varanus macraei was discovered recently like many other species of treemonitors. The last few years other members are added to the group of the treemonitors, most recently Varanus reisingeri was added (2005). Animals live solitary and group during the mating-season. Very little is known about breeding treemonitors, Varanus macraei especially. What is known I will share with you in this caresheet.

These arboreal monitors are inhabitants of tropical and sub-tropical parts of the World. In these parts of the world temperatures vary between 25 and 40 °C, with extreme high levels of humidity (between 80 % and 100 %). Nighttemperatures don’t vary much from daytempratures, my own experience has made clear that deze lizards can be kept at room temprature at night (15-20°C).

The total length of this monitor is between 90 and 110 cm (head-to-tail-length). Almost 2/3 of the length of the lizard is tail. The base-colour of the body is black with blue cirkels the snout of the lizard is nearly white. The belly of the monitor is almost white. Their tail can be used as a 5th limb, just as a monkey. They can wrap it around a branch to stay stable when climbing trees.
The difference between male en female treemonitors is difficult to make. A few external features can help you to determine to sex an animal. Male lizards have bigger heads and are bigger in general. If you get the chance to see the animals up close you can see the hemipenises of the man, as two bulges under the tail (females lack these bulges).
The only feature that really helps you with determining the sex of an Varanus macraei and that the shape of the lower jaw. Males have a slightly bent lower jaw, where the lower jaw of a female is nearly straight (see the pictures).

I keep my pair in an enclosure of 100 cm long, 125 cm wide en 220 cm high. The enclosure walls are made with styrofoam and cement so they can climb a lot. The substrate that I use for the ground was Reptibark, because of the way it stays moist. Also I put in a bunch of cork-pieces and some tropical plants. I strongly advise against using real plants in an enclosure of a larger active lizard, plants don’t last very long. As lighting is used a 100 watt T-rex Active UV heat bulb and a regular lightbulb of 100 watt. This provided the animals with heat spots of approximately 48-55 °C, where the animals lie a few hours a day. Averagbe temperatures in the enclosure are about 28 °C. I offer the animals 12 hours of light a day.

I feed my pair 3 times a week. Diet consist of mainly grasshoppers and rodents. Sometimes I offer crickets and dola’s. Cockroaches are also very suitable as food for these lizards, but because roaches can become a pest I don’t feed them. Two times a week I powder the food with a mixture of calcium and vitamins. I spray the enclosures firmly once or twice a day (depending on the season). Is also offer the animals a bowl of water, to give the monitors plenty of opportunity’s to drink. This of one the most important parts in successfully keeping treemonitors. Enclosure-humidity needs to be between 80-100 %. I advice to keep the animals in pairs, or if the enclosure is big enough in threesomes (1.2). The Varanus macraei is a nervous lizard and plenty of space gives the animal the chance to become less nervous.
An other important measure that needs to be taken care of is the amount of vertical climbing-space, these animals live in trees in their natural habitat and need to be able to show this behaviour in captivity to. Providing areas in the shade is also important for these animals, they tend to feel very secure in areas in the enclosure that are less light.
I also keep close attention on the behaviour of the animals, when the animals are less active and timid than this is ussualy because the humiditylevel isn’t high enough. You can increase huimidity-levels by increasing the amount of spraying or to decrease the ventilation in the enclosure.

Breeding experience
The animals are sexually mature after about 1.5 years. I have had no successful mating attempts but I hope to see this, this year. There are a few ways till stimulate your animals to mate. First there is the principle of separating the animals for a certain period (6 weeks is a good period). In some cases quickly after reintroducing the animal, copulation can be witnessed. You can also try to introduce a rain season with your animals. The way you can try to do this is by first keeping the animals at a reasonably low humidity level, approximately 60 – 70 %, for two or three months. After this time you start to spray the enclosure regurly, to increase the humidity level to 90 – 100 %. The animals could start to mate in the wet period.
After a succesfull copulation, most copulations appear hanging form the wall, vertically. When a period starts in which mating occurs, you can spot this because the animals will be close to one and other.
6 weeks after copulation the female lays her eggs in layingcontainer, usually. The best way to make a laying container is to take a fairly big box and filling it with moist sphagnum.After laying you should take away the eggs as soon as possible, because Varanus macraei will eat its own eggs.

Incubation of eggs of tree monitors is very difficult. I am one of very few people who have succeeded in successfully breeding these animals. My successes have been achieved by using vermiculite of perlite in a 1: 1 ratio (vermiculite/perlite: water). Eggs need a long time to incubate, approximately 180 days at 29 and 29,5 °C .

The juveniles are an exact copy of the parents. They’re beautifully coloured blue and black. The animals start feeding after approximately 1 week, they eat crickets and baby mice. Feeder-animals need to be powdered as often as possible with a mixture of vitamins and calcium, UV-light is advised. Each day clean drinking water needs to offered, twice a day the animals need to be sprayed with water (not to cold). In literature it is said that these young animals can only be raised separately but I have raised them in groups without any problems.


Great animals with an extraordinary appearance, this one of the lizards where you can see that the great-great-grandfather were dinosaurs. Because the animals have a tail which they can utilise in climbing, you can see the animals roaming through the enclosure. Reptile-lovers should know that these monitors can’t be handled without wearing gloves, because the animals make nasty scratches and nasty bites. But this temperament also is what makes these animals such great creatures to keep in the hobby.


Eidenmuller, B, 2003, Warane lebensweise, pflege, zucht, Offenbach:Herpeton, 2003, p. 86.

Dedlmar, A, Haltung, Pflege und Nachtzucht von Varanus Macraei, Reptilia nr. 63 Februari/Maart, jaargang 12, p.39/41.