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Monitor Lizard Ownership: Important Points to Consider

Lace monitors fighting

Uploaded to Wikipedia Commons by John Hill

Each of the many monitors under my care at zoos and in my own collection has left me with the feeling that they are somehow “more complicated” than other reptiles. Recent research into their breeding and hunting strategies bears this out…monitors do indeed appear to be the most advanced of all lizards. Pets often become unusually responsive to their owners, who sometimes ascribe mammal-like qualities to these fascinating reptiles.


Among the monitors we also find the world’s largest lizards, a fact which adds to their allure. But giants such as the Water, Lace, Crocodile and Nile Monitors are tough to manage even in zoos, and are suitable only for those few keepers with the knowledge, space, maturity and finances to meet their needs. More importantly, it must be understood that all monitors can inflict severe injuries…in fact, fatalities are a real possibility where young children or incapacitated adults are concerned. Today I’ll review some important points that, if considered beforehand, will greatly improve life for both monitor and monitor owner. As always, please be sure to post any questions or thoughts below.


Crocodile Monitor

Uploaded to Wikipedia Commons by Greg5030


While monitors vary greatly in personality – some become rather docile, while others remain wary of people – all can be dangerous and must be treated with caution. They are certainly capable of learning from experience and altering their responses to people. My experiences in zoos with Crocodile and Water Monitors illustrated this very clearly to me (please see articles linked below). However, this should not lead us to “trust” them, or to treat a monitor, or any reptile, as though it were a well-trained dog. The following quote from legendary snake expert Bill Haast is generally applicable to any reptile: “You can have a snake for 30 years, but leave the cage open once, and it’s gone – and it won’t come back unless you have a mouse in your mouth”!


Large species such as Crocodile, Water, Lace and Nile Monitors (V. salvadorii, V. salvator, V. varius and V. niloticus) can be dangerously aggressive and are not suitable for most private collections. In the course of my work as the Bronx Zoo’s head mammal keeper, I helped restrain giraffes, bison, polar bears, rhinos and many other formidable beasts…but Water Monitors are, pound-for-pound, one of the strongest animals I’ve ever handled. Large monitors can inflict severe bites and scratches, which can lead to permanent injuries and life-threatening infections. Operating policies in most zoos require that 2 experienced keepers be present when monitor exhibits are entered.


Water Monitor

Uploaded to Wikipedia Commons by Beijingbing


Monitors are quite active, and languish in cramped enclosures. Also of concern is the fact small cages render it difficult to establish a temperature gradient (thermal gradients, critical to good health, allow reptiles to regulate their body temperature by moving between hot and cooler areas). Most species require very high basking temperatures, and if sufficient space is not provided, the entire cage will become over-heated due to the effects of the basking site.


The 6 to 7 foot-long Nile, Lace, Crocodile and Water Monitors require room-sized enclosures with drainable pools. Even moderately-sized species, such as the Rough-Necked Monitor (V. rudicollis), should be provided with a living space measuring 6’ x 6’ x 6’ or greater.



The initial purchase price of your pet and the expenses involved in constructing a custom-built enclosure are only a small portion of the total cost involved in monitor ownership. Electricity use will be substantial, veterinary care is as or more expensive than for a dog, and food (mainly rats and, for some, whole fishes) continues to climb in price.


Veterinary Care

Reptile-experienced veterinarians are difficult to find in many regions, and not all will be willing or able to treat a large monitor. Trust me – it is a grave mistake to embark on monitor ownership before locating a veterinarian, or to imagine that even the hardiest of species will not require medical care. Please post below for a list of herp-experienced vets in your area.


Nile Monitor

Uploaded to Wikipedia Commons by A. C. Tatarinov

Time Commitment

While all reptiles require daily checks as to their condition, many require very little in the way of actual daily or even weekly work. Large monitors need a great deal of care, usually on a daily basis…think more in terms of an annoying puppy (sorry, dog-people!) with dangerous teeth and claws rather than a well-fed, oft-fasting Ball Python.


Remember also that monitors may live into their 20’s, and that the amount of work and degree of expertise they demand usually complicates the task of finding appropriate care while you are away from home.

Hi, my name is Frank Indiviglio. I’m a herpetologist, zoologist, and book author, recently retired from a career spent at several zoos, aquariums, and museums, including over 20 years with the Bronx Zoo.

Please check out my posts on Twitter and Facebook.   Each day, I highlight breaking research, conservation news and interesting stories concerning just about every type of animal imaginable. I look forward to hearing about your interests and experiences as well, and will use them in articles when possible.


Please also post your questions and comments below…I’ll be sure to respond quickly. Thanks, until next time, Frank.


Further Reading

Monitor & Rhino Iguana Learning Abilities


Black Rough Neck Monitor Care



Black Rough Neck Monitor Care and History

Although the Black Rough Neck Monitor, Varanus rudicollis, is rarely-seen in the wild, captive-bred individuals are often available.  This striking lizard utilizes a variety of very different habitats, so in a suitably large enclosure one can expect to see a many interesting behaviors.  This is definitely a species worth studying carefully, as we still have much to learn.  I’ve always wanted to feature them in large zoo exhibits, but was not able to drum up much interest, unfortunately.  Private keepers, however, have added greatly to what is known of this under-appreciated monitor.

Black Rough Neck Monitors remind me of Merten’s Water Monitors, Vanaus mersentsi, in general body form and especially in their ability to move about in trees, water and on land with equal ease (Note: the photo below is of a Merten’s Water Monitor; please click here for photos of Rough Neck Monitors)


Riverside rainforest habitat

Uploaded to Wikipedia Commons by Allie Caulfield


The Black Rough Neck Monitor is found across a huge range that extends from southern Myanmar through Thailand and western Malaysia to Sumatra and Borneo, and also inhabits nearby offshore islands.  As it is difficult to observe, many believe that the range is greater than generally accepted.



Although widely distributed, the Black Rough Neck has specific habitat requirements.  It seems restricted to rainforests near permanent water bodies and mangrove swamps.  Although believed to be highly arboreal, Black Rough Necked Monitors frequently forage on the ground and in the shallows of rivers and swamps.


Merten's Water Monitor

Uploaded to Wikipedia Commons by Jarek Tuszynski /


The Black Rough Neck Monitor is stout in build and averages 3-4 feet in length, with some individuals reaching 5 feet.  The body color ranges from dark gray to nearly black; there is some evidence that different populations exhibit specific shades of gray or black.  The thick, pointed scales that encircle the neck are unique among monitors; I’ve not yet found a reputable published account of their function.  Extremely sharp claws (even by monitor standards!) assist it in climbing.



Like most monitors, Black Rough Necks are quite active, and will not thrive in close quarters.  Adults require custom-built cages measuring at least 6 x 4 x 6 feet; greater height is preferable.


Cypress mulch or eucalyptus bark may be used as a substrate.  Shy by nature, they are best provided with numerous caves, cork bark rolls and hollow logs in which to shelter, and stout climbing branches for climbing.  They prefer sheltering above ground (wild individuals often utilize tree hollows), so a cork bark roll or large nest box positioned among the branches would be ideal.


The cage should be located in a quiet, undisturbed area of the home, as Black Rough Neck Monitors are very aware of their surroundings and easily stressed.



Black Rough Neck Monitors fare best when afforded a wide temperature gradient, such as 75-95 F; a dip to 70-73 F at night may be beneficial. The basking temperature should be kept at 120-140 F; some keepers go as high as 150F.  Incandescent bulbs http://www.thatpetplace.com/spot-day-white-bulbs may be used by day; ceramic heaters http://bitly.com/NSUMSq or red/black reptile “night bulbs” http://bitly.com/MS35s9 are useful after dark.


Provide your monitor with the largest home possible, so that a thermal gradient (areas of different temperatures) can be established.  Thermal gradients, critical to good health, allow reptiles to regulate their body temperature by moving between hot and cooler areas.  In small or poorly ventilated enclosures, the entire area soon takes on the basking site temperature.



Humidity should average 60-85%, but dry areas must be available.  A commercial reptile mister will be helpful if your home is especially dry.  A water area large enough for soaking must be available.



UVB exposure is essential.  If a florescent bulb is used (the Zoo Med 10.0 UVB Bulb is ideal), be sure that your pet can bask within 6-12 inches of it.  Mercury vapor and halogen bulbs broadcast UVB over greater distances, and provide beneficial UVA radiation as well.




The few available studies and observations indicate that wild Black Rough Neck Monitors take a wide variety of prey animals, and that the diet may vary across the range.  Rodents, bats and other mammals, although consumed when available, do not comprise the bulk of the natural diet.  Wild individuals seem to feed primarily upon grasshoppers, roaches and other large insects, frogs, crabs, and snails.  Scorpions, termites, birds and their eggs, and fish have also been recorded as being consumed.


A rodent-only diet will not work well for Rough Necked Monitors. Youngsters should be fed largely upon roaches, super mealworms, snails, hornworms and other invertebrates, along with small whole fishes, un-shelled shrimp, fiddler and green crabs, crayfish and squid.  Mice should be provided once weekly, and hard-boiled eggs can be used on occasion.  All meals offered to growing monitors should be powdered with calcium, and a high-quality reptile vitamin/mineral supplement should be used 3x weekly.  I favor ReptoCal, ReptiVite and ReptiCal.


Rodents and whole fish can comprise 50% of the adult diet, with a variety of large insects, hard-boiled eggs, crayfish, squid, shrimp, snails and similar foods making up the balance.  Calcium and vitamin/mineral supplements should be used 1-2x weekly.  Large food items should be avoided; even where adult monitors are concerned, mice are preferable to small rats.



Although not a species for beginners, Black Rough Neck Monitors adjust well to captivity when given proper care, and make fine, long-lived pets.  Initially shy, some learn to trust gentle caretakers, while others remain wary even after years in captivity.  A large, well-furnished cage will provide the security which is essential if they are to become approachable.


In common with all monitors, they are capable of inflicting serious injuries with their powerful jaws, long tails, and sharp claws.  Thick leather gloves should be worn when handling Black Rough Neck Monitors, as even tame individuals will cause deep scratches with their claws in the course of their normal movements.



A single male can be housed with 1 or 2 females, but they must be watched carefully.  The nesting area should be enclosed (i.e. a large tub or plastic storage container within a wooden box equipped with a single entrance hole) and stocked with 2-3 feet of a slightly moist mix of sand and top soil or peat moss.


Egg deposition generally occurs within 35-50 days of mating, but captive conditions can greatly affect the gestation period.  Clutches contain 4-15 eggs, which may be incubated in moist vermiculite at 85-90 F for 180-200 days.  Double and triple-clutching has been recorded. Hatchlings measure 8-11 inches in length and are attractively banded with yellow.


Please check out my posts on Twitter and Facebook.   Each day, I highlight breaking research, conservation news and interesting stories concerning just about every type of animal imaginable.  I look forward to hearing about your interests and experiences as well, and will use them in articles when possible.


Please also post your questions and comments below…I’ll be sure to respond quickly.  Thanks, until next time, Frank Indiviglio.


Further Reading

How to Feed Insect-Eating Pet Lizards – the Best Live Foods

Hello, Frank Indiviglio here.  From tiny Day Geckos to stout Water Dragons and lumbering Savanna Monitors, many popularly-kept lizards feed primarily upon live foods including insects and other invertebrates. The most important point for insectivorous lizard owners to remember (and one that my regular readers are sick of seeing!), is that crickets and mealworms alone, even if powdered with supplements, are not an adequate diet for any species.  Dietary variety is essential.  Fortunately, with a bit of planning, we can collect, breed or purchase a huge array of nutritious invertebrates for the lizards in our collections.

Beetle grub

Uploaded to Wikipedia Commons by Toby Hudson

From specialists such as Horned and Caiman Lizards to Tokay Geckos and other generalists, the needs of individual species vary greatly.  Please post below for specific information on the lizards in your collection.

Wild Caught Insects

I firmly believe that reptile keepers should place much more emphasis on collecting insects and other invertebrates.  While caution concerning pesticides and toxic species is warranted (please see articles linked below), the risks can be managed. Some notable successes that I and colleagues have had with a variety of delicate reptiles can be credited in part to the use of wild-caught insects. Read More »

Monitor Lizard Care, Natural History and Behavior – An Overview

Nile MonitorHello, Frank Indiviglio here. I’ve had the good fortune of caring for 15-20 monitor species during my zoo career. From the diminutive Storr’s to the massive Water, Lace, Crocodile and Komodo Monitors, all have instilled in me the feeling that they were, somehow, “more complicated” than other reptiles. Indeed, recent studies have confirmed that they are, among lizards, highly advanced.  While some are too large for the average household, several moderately-sized and even dwarf varieties are being bred by hobbyists, and all make fascinating and responsive captives.

The following information can be applied to the care of Savannah, Black Tree, Nile, Merten’s and most other monitors.  However, details vary; please post below for information on individual species, and be sure to add your own thoughts and observations on monitor lizard care.

Natural History

Seventy-three monitor species (Family Varanidae) range across Asia, Africa and Australia. Nile Monitors (Varanus niloticus), introduced to south Florida, are a major environmental concern there.  Lace Monitors (V. varius) and other large speciesare usually the dominant predators in their habitats.  While most dwell in warm regions, Desert Monitor (V. griseus) populations in Kazakhstan are adapted to Vermont-type winters.  Read More »

World’s Smallest Frogs Added to 2011’s List of Newly-Discovered Amphibians

Eleutherodactylus iberia
Hello, Frank Indiviglio here.  Two frog species recently discovered in southeastern New Guinea are smaller than any other 4-legged vertebrate.  Within their pea-sized bodies, they pack a brain, lungs, heart, digestive system and most of the other organs that people have…simply astounding!

Tiny Frogs and Fish

The frogs, Paedophryne dekot and P. verrucosa, were collected several years ago, but were only described as new species this year (please see ZooKeys article).  Among all the world’s vertebrates, only a single fish, a Southeast Asian relative of the carp (see amazing photo here) is smaller – and the new frogs exceed it in size by only 0.1 mm!  Another contender for the title, a leaf-litter frog from Cuba (please see photo of striped frog), is only a tiny bit larger. Read More »

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