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There are a few species in the Mangrove monitor complex that sport a blue tail during part or all of their lives but Varanus doreanus is the true Blue-Tailed monitor. This moderatly large varanid can be found in New Guinea as well as some of its surrounding islands. There are two known variations of the Blue-Tailed monitor; Varanus doreanus doreanus and Varanus doreanus finschi. The later is found on New Britain and the Bismarck-Archipelago. Varanus doreanus finschi differs from the other form in that it possesses a white throat instead of the marbled pattern found on Varanus doreanus doreanus (Bennett, 1998). Varanus doreanus finschi may truly be its own species. These monitors inhabit forest regions where temperature and humidity are high. They are very good climbers and do show aquatic tendencies. These factors should be considered when designing an enclosure.
Blue-Tailed monitors seen in the pet trade are usually wild caught and should be treated for parasites and bacterial infections by a qualified veteranarian if they arrive in bad shape. If the animal is in good shape and eating well when it arrives the vet check may not be entirely neccessary. I've had many monitors do well in captivity without a de-parasiting, but then its better to be safe than sorry. If you look around you may also be able to purchase a captive bred Blue-Tailed monitor. A captive bred monitor should always be the first choice when its available. By purchasing a CB (Captive Bred) instead of a WC (Wild Caught) monitor you have a better chance of getting a healthy animal.
The color and pattern of Blue-Tailed monitors are all fairly similar with a few exceptions. The base color is usually black with yellow spots that form bands or an irregular pattern on the dorsum (top). The tail is typically 1.5 times longer than the body and is colored in blue for about the last three quarters of it. The limbs are powerful and well equiped for tree climbing with very sharp nails. The legs are speckled with yellow and blue and the belly (underside) is marbled. The head is black, sometimes with verticle bands crossing the snout. There is also another dorsal pattern that I've noticed on some specimens that looks more attractive than the yellow on black. It shows considerable amounts of grey, forming a messy net pattern on top of the black base but the yellow dorsal spots remain the same (see skin panel on the side). In general, these patterns will become darker as the animal ages. The Blue-Tailed monitor has a white to yellow tongue that can be used in part to distinguish it from other Mangrove type monitors.
Varanus doreanus comes from a tropical climate where humidity and heat are both found in steady abundance. Thier enclosure should have a warm ambient temperature which can be achieved by using heat lamps, flood lights (incandescent), or ceramic heaters that emit no light. Depending on the size of your enclosure you'll need to figure out which combination of lamps and in what wattages will be needed to provide your monitors with the proper cage temperature. If you see that the heat lamps don't sufficiently light your enclosure you will need to either use an additional low wattage incandescent bulb or install a flourescent fixture to provide the needed light.
Blue-Tailed monitors will need an ambient cage temperature in the range of 82-86°F. The basking site itself should be around 110-120°F. Be sure to allow for a temperature gradient in the tank and not a uniformly hot enclosure. The basking spot should be on one end of the tank so that a natural gradient is formed. Also, I find that by using slabs of various rock placed under the heat source you can provide your monitor with a good source of heat since the rock captures and distributes the heat evenly. You will have to experiment with different wattages of bulbs to find one that won't overheat the rock which can lead to thermal burns. If done correctly, this type of basking spot will allow a Blue-tailed monitor to quickly reach its desired body temperature. Warning: Make sure your Blue-Tailed monitor can not come into direct contact with the heating element because it can severely injure itself. Their sense of touch is not the same as ours and the monitor may burn itself without knowing it. Use some sort of screening or make sure the heating device is far enough away that the monitor can't reach it.
A regular photoperiod of 12 hours light : 12 hours dark can easily be achived with the use of a simple timer that can be purchased at any hardware store. Don't be affaid to experiment with this cycle to see if there is a better light to dark ratio for your monitor or if it makes no difference at all. I won't get into the whole issue of whether or not monitors need UV lighting, except to say that there is no definitive proof to show that they need it in captivity or to show that they suffer from receiving it. Many people have successfully kept monitors both ways. You can do some research and make your own informed decision on this one.
During the night the temps should not be allowed to drop below 70°F. Depending on where you live in the world you may have to take precautions to avoid letting your monitor get too cold at night. You can use red or purple "night" bulbs or non-light emitting ceramic bulbs to do this or you may find it more effective to use a room heater. If you have a monitor room the later option is probably most effective.
Varanus doreanus is a moderatly large monitor that likes to climb and soak and will require an enclosure that gives it sufficient room to move around and do all of these activities without feeling cramped.
As juveniles, Blue-Tailed monitors can easily be housed in 20 gallon aquariums. If they are well fed they will outgrow a cage of this size in a matter of months and will need to be transferred to a new enclosure. You can easily build a nice looking and functional cage out of melamine and glass. It is always best to build the largest cage possible but as a minimum, an enclosure with dimensions 6 feet long X 3 feet high X 2.5 feet deep will house an adult Blue-Tailed monitor. This is only a suggestion . Of course the more space you provide them with the better off they will be.
Varanus doreanus like to climb both as juveniles and adults. You should keep this in mind when constructing and designing their enclosure. You can suspend thick branches in the enclosure and you'll find they make good use of them. Make sure that are are securely fastened so that they don't come undone when the monitors are climbing or hanging on them. By positioning a branch under a basking spot you will probably see your monitor lounging there on a regular basis.
Blue-Tails also enjoy a water bowl they can submerge themselves in and soak. They will curl their tail around and remain there for a very long time if the water is kept warm. They will also defecate in warm water so regular cleaning and disinfecting of the water bowl is neccessary. Defecating in the water bowl is a plus for cleaning purposes but not all monitors will do this regularily. Feces should be cleaned out of the tank as soon as possible and not left in a water bowl or on the substrate for long periods of time. Various sized cat litter boxes make good water bowls that are easily cleaned.
There are numerous substrates available for a keeper to choose from when dealing with Varanus doreanus. Good choices include aspen shavings, cypress mulch, dirt, leaf litter, and mixtures of these. It is important to have a substrate the monitors can dig in and bury themselves under. For them to bury successfully you are going to have to make it at least a few (4-5) inches deep. I use cypress mulch for my Blue-Tailed monitor because of its ability to hold moisture and its esthetic value. If you do not mist cypress mulch it tends to dry out and can produce a lot of dust. This should and can be avoided by misting the enclosure with a spray bottle or pressurized canister that you can buy at any hardware store.
When the are hatchling-juvenile sized, they tend to be shy animals and will hide for quite some time until they become well acclimated to their surroundings. Even then they will still choose to remain hidden much of the time. You should provide hiding spots for then in different parts of the tank so they will have somewhere to retreat to if they feel threatened. Hiding spots can take the form of commercial hide boxes or half logs or any number of other suitable hideaways. Just be sure that whatever you use is large enough for the monitor to fit its entire body into and feel safe.
Some juveniles tend to be very shy feeders and will only eat the food you offer them when they are sure you are not around. Others will eat with an indiffernece to your presence. As long as your animals are eating well and getting a varied a diet it really makes no difference if they eat infront of you or not, but it's always nice to be able to watch a monitor eat.
My animals tended to be picky eaters as juveniles and would not accept any insects. They would however, eat mice without a second thought. I've also seen Blue-Tails that feed excitedly on insects and any other prey items offered to them. As a guide, these are some acceptable prey items that may be accpeted by Varanus doreanus. As juveniles you can feed them crickets, mealworms, eggs, mice (appropriate size) and ground turkey. As subadult-adults they can be offered crickets, mealsworms, eggs, ground turkey, mice, rats (appropriate size), chicks, crustaceans and various seafood. Note: Fresh water should be available at all times
Varanus doreanus is a moderatly large monitor lizard that can move surprisingly quick. As hatchlings they would measure in somewhere in the range of 7-9 inches TL. Adult Blue-Tailed monitors have been reported to measure up to 5 feet TL but on the average they will grow from 4-4.5 feet TL. The animals seen in the pet trade are usually (WC) wild caught juveniles. They can move very fast are are fairly strong so a wild caught adult should be handled with caution. These monitors can become obese just like most others of overfed in adulthood. In general they are heavily built and possess stout limbs and a thick tail. This is a beautiful monitor to keep.
Juvenile monitors of this species are usually nervous or shy but tend to calm down considerably with regular, gentle handling. If you want to have the type of monitor you can handle reasonably as an adult I would suggest buying a juvenile and working with it from an early age. Defensive behaviour in juveniles include biting, scratching, and defecating. Juveniles tend not to tail lash as readily as other species but instead choose to flee before using any of these other options.
Most adult Blue-Tailed monitors in captivity are usually wild caught and not long term captives. This makes them very shy animals that will need good husbandry practices and a lot of time to properly acclimate to their new surroundings. Defensive behaviour in adults include tail lashing, biting, scratching, defecating and of course hissing. Given time these initially nervous animals will calm down to a point where you can handle them with a minimal amount of worry.