By Robert George Sprackland, Ph.D.
Perhaps you have been successfully keeping savannah monitors and now seek a new challenge. A logical intermediate step is to take on the care of a species whose needs will help you bridge the gap between experienced novice and expert status. The cover of the August 2006 issue of REPTILES carried the question: “Do you have what it takes to keep a green tree monitor?” — a lizard almost universally accepted as among the most difficult to care for in terrarium conditions. Peach-throat monitors (Varanus jobiensis) are among the varanids that make good intermediate terrarium challenges, provided they have the necessary room, temperatures and privacy.
Peach-throats are partially terrestrial, like savannah and spiny tailed monitors, but spend considerable time in trees and along riverbanks. They attain a larger adult size than savannah monitors — up to 48 inches overall — but are lighter, sleeker animals. It is a rare peach-throat that can be called tame, but once acclimated to terrarium conditions, they are far more sedate than their green canopy-loving kin. They consume both live and prepared foods, come in a variety of color patterns and are generally priced somewhere between spiny tailed and green tree monitors.
About the Peach-throat
The Australasian region, which encompasses Australia, the entirety of New Guinea, the Solomons and islands between Sulawesi and New Guinea, is home to a large and growing number of Varanus species known as tree and mangrove monitors. Several species have been described since 1990, and others await published descriptions even now.
The tree monitor group contains elongate, long-tailed lizards that typically spend all or most of their lives high in trees; they possess a cylindrical tail that is a fully prehensile grasping organ. The mangrove monitors include bulkier species that are often found on the ground, yet climb and swim well, and have laterally compressed tails.
When the peach-throat monitor was first described in 1932 from a young, alcohol-faded specimen in a Berlin museum, it was classified as a subspecies of the wide-ranging mangrove monitor (Varanus indicus). In 1951, another German herpetologist described similarly faded adults from a Chicago museum and named them V. karlschmidti. By the 1990s, several researchers had live animals to compare with museum specimens, and the lizard was given status as a species quite distinct from V. indicus. It is formally known as V. jobiensis. The Latin name comes from the type locality, Jobi (currently Yapen) Island north of western New Guinea, but the lizard is actually widespread across much of New Guinea and some nearby smaller islands.
Peach-throats appear similar to other mangrove monitors, but are distinguished by a dark, patternless head, large round eyes, a pink tongue and a pronounced, dark longitudinal stripe through the eye. The dark upper portions of the head are slightly lighter than the dorsum. The throat and, often, temporal regions are light salmon. The throat is pale white and unpatterned. Young are more intensely colored, with much of the temporal and gular regions bright pink, and the light markings on the tail tend to be very broad. The snout is more slender, with sharper edges, than that of similar species. The tail is long, but not nearly so long as seen in tree monitors; peach-throats’ tails are 1.48 to 1.9 times snout-vent length (SVL), while in tree monitors the length typically exceeds 2.2 times SVL.
Color and pattern variations are numerous. The dark brownish-olive dorsum is covered in small, pale yellow spots. The spots generally cluster into ill-defined dorsal bands, with dark unmarked regions in between, but in many animals the banding is absent. The distal third of the tail usually sports broad bands of black and a light color, ranging from white to pale yellow to gray to light blue to turquoise.
Large Cages Required
Newly acquired peach-throat monitors, especially those that are wild caught, tend to be hyperactive, nervous lizards. It is absolutely essential that they have a large terrarium with lots of hiding places. Unlike the sluggish savannah monitor, this is a large, active species that will explore the cage for hours or dash madly away from an intruder.
Even acclimated specimens will rub their snouts raw (and worse) against screen, so you must provide a cage design that keeps lizards and ventilation holes apart. For similar reasons, cage materials should be rugged and not prone to chipping or splintering.
Because these lizards are active in both horizontal and vertical planes, the terrarium must allow considerable floor space and height. Dimensions should be at least 10 by 61/2 feet of floor space and 6 1/2 feet tall. The terrarium floor should be waterproof with a low lying drain, and should also be able to contain contain soil or water without leaking.
Peach-throats and other mangrove monitors come from habitats that have just two seasons: a long rainy season (from December to March or April) and an equally long dry season (from April to November). However, the lizards live near water, so that even in the dry season, the humidity is still quite high. Keep the terrarium humidity at 80 percent during the dry season and 95 to 100 percent during the rainy season. To retard mold and keep air quality clean, there must be some degree of lateral air flow, which may be facilitated by use of a small electric fan for a few hours each day.
The terrarium should contain a large pool of clean fresh water that can be easily and regularly drained and replenished. Peach-throats are not as aquatic as some of their relatives, but they will spend considerable time soaking in a small pool. Water should be at room temperature or above, and kept free of algal and other growths. Live aquatic plants may have a decorative function, but are likely to be destroyed and carted around the terrarium by the lizards. Monitors may also pursue and eat live fishes put in a pool.
Heating and Lighting
Like most mangrove group monitors, peach-throats bask in direct sunlight for short periods of time, but are more likely to perch on partially exposed branches, fallen trees or riverbanks. The terrarium should therefore offer a heat lamp, but with plenty of shady spots underneath. The upper third of the enclosure should be heated to 85 to 105 degrees Fahrenheit, but the lowest level should stay below 85 degrees. Nighttime temperatures may drop by 5 to 10 degrees.
A nighttime heat lamp, whether ceramic or red, is not suggested, as lizards experience temperature fluctuations in the wild and should do so in captivity as well. Additionally, wet season rains are quite cold, so temperature fluctuations during a simulated rainy season may swing more than those of the dry season. Parameters should be between 76 and 88 degrees.
Full-spectrum ultraviolet (UV) light should be provided, and is essential if breeding is planned. Ultraviolet light has been linked to increased blood calcium levels in diurnal reptiles. (In humans, UV is essential for the chemical conversion of dietary vitamin D into activated vitamin D, without which we could not absorb and use any of our calcium supplies. It is still unknown if reptiles have a similar essential biochemical process, but it is known that there is a positive correlation between reptile UV exposure and blood calcium levels.)
Because calcium is essential for structural repair and physiological processes, such as nerve impulses, bone maintenance and muscle contractions, the use of full-spectrum lighting for healthy captive animals is essential. UV light is not required constantly; experimental data shows that even 30-minute daily doses are adequate for keeping blood calcium levels up. Signs of calcium deficiency include lethargy, sluggishness, weakness and appetite loss.
Peach-throats require a broad central climbing object, such as a tree trunk, and horizontal branches strong enough to bear their weight. Cage accessories must be both strong and durable, as they must be able to support strong, active, sharp-clawed lizards, and you do not want to replace them often. If possible, a sturdy tree trunk makes an ideal central prop, as it is broad enough to provide cover. If hollow, it also offers a natural hiding area. Natural branches are a plus, but strong artificial branches can be bolted to a trunk.
Each lizard requires its own perch (though they may pile atop one another on occasion). Perches should be wholly or partially shaded, and placed at different levels. Lizards thermoregulate by moving to perches at different levels, the warmest being the highest and nearest the heat lamps.
Peach-throat monitors prefer basking in shade or slightly exposed spots. Shade should come from plastic leaves and vines — natural materials will quickly be shredded by the lizards’ sharp claws. Large live potted plants may do well if firmly anchored (or weighted) on the terrarium floor. Large ferns and young palms would be especially good choices, providing cover as well as natural decoration.
All monitors benefit from a thick substrate, where they excavate for food or lay eggs. The biggest downsides to substrates are keeping them clean and the messes that result from lizards flinging soil everywhere. If breeding is a goal, though, a deep, 2- to 3-foot layer of soil is important. Use a fine potting soil or soil-clay mixture that retains some moisture. The lowest few inches should be the most moist, and evaporation and humidity should keep upper layers slightly moist. Substrate of the proper consistency is solid enough to allow lizards to dig semipermanent burrows.
As with all other varanids, peach-throats are primarily carnivorous. Wild specimens feed primarily on insects, but also consume small frogs, small eggs and spiders. Because they are also very active lizards, their nutrition and caloric demands make it important that they are fed daily or at least every other day. Young lizards should be fed live insects — such as crickets, roaches, mealworms and waxworms — that have been fed a diet of fresh greens and cereal, and dusted with vitamin and mineral supplements. Larger young lizards may additionally be fed small rodents, fresh shrimp and fish strips, and bits of precooked sausage. Young lizards should be fed daily.
Adults accept many of the same foods as the young, but insects fed to adults must be larger in size. If you are able to secure live local grasshoppers, locusts, beetles and stick insects, these make excellent supplements to the standard diet. Offer freshly killed or thawed frozen rodents, eliminating the possibility of the rodents biting and injuring the monitors.
Other acceptable foods include canned and moistened dry dogfood, canned lizard diets, hot dogs and cooked eggs. Though these lizards will take strips of raw beef or chicken, the high likelihood of contracting Salmonella infection makes these food items extremely poor choices. Feed adults five days out of seven, and avoid offering large feedings at one time. Unlike snakes, captive varanids are not generally going to thrive on widely spaced large meals.
There is controversy over the use of vitamin and mineral supplements in reptile diets, particularly as many mineral supplements cannot be absorbed unless they come in a form found in natural foods. Many herpetoculturists suggest that gut loading food animals is the best way to insure adequate nutrition for reptiles. I feed all insects a diet of green leafy vegetables, mashed fruits and crushed cereals that are dosed with vitamin and mineral supplements. These insects are then fed to lizards after a 24-hour feeding period. Rodents are similarly fed a nutrient-rich diet, or freshly thawed specimens are packed with liquid vitamins and dusted with calcium and phosphorus powder.
If you have or plan to acquire Varanus jobiensis for your collection, you will have a fairly hardy, active and colorful display animal. With very little time, peach-throats become much more calm than the related tree monitors and are more likely to be active — not frantic — in your presence. If all goes well, peach-throat monitors may be expected to live for nearly 20 years, so consider their acquisition a long-term investment.