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Monitor Lizard Care, Natural History and Behavior – An Overview

Nile Monitor 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. 

The 8 inch-long Short-Tailed Monitor (V. brevicauda), is the smallest member of the group.  The Komodo Dragon (V. komodoensis), the world’s largest lizard, occasionally tops 10 feet in length.

Monitors take prey ranging in size from termites to deer.  The recently-discovered Sierra Madre Forest Monitor (V. bitatawa) and the Philippine Monitor (V. olivaceus) are unique in consuming fruit, while the Komodo Dragon has attacked and killed people.

In 2005, it was discovered that several species produce venom that affects their prey’s blood pressure and clotting ability.

Five new species, one topping 6 feet in length, have been described in the past several years (please see articles below).


Monitors are ever-alert, and easily startled by noises and sudden movements. They vary greatly in personality – some become quite docile, while others remain wary of people. All are very responsive, and quickly learn to anticipate regular feeding times.

Water MonitorCrocodile and Water Monitors (V. salvadorii and V. salvator), and other large species, can be dangerous and are not suitable for most private collections.  Adult Water Monitors are, pound-for-pound, one of the strongest animals I’ve ever restrained (I was the Bronx Zoo’s head mammal keeper for a time, and so thought I could handle most anything!). All monitors can inflict severe bites and scratches. The mouth and tail (which is whipped about in self-defense), should never be allowed near one’s face.  Operating policies in most zoos require that 2 experienced keepers be present when large monitor exhibits are entered.

New monitor facts frequently come to light.  Recently, a Black Tree Monitor was observed using its front foot to extract an insect from a crevice; this behavior has not been documented in any other lizard.


The Enclosure

Hatchlings and small species, such as the 14-inch-long Storr’s Monitor (V. storri), may be housed in 30-55 gallon aquariums.

Merten’s Monitors (V. mertensi) and others in the 3-4 foot range are best kept in homemade cages measuring at least 4x4x4 feet.  Height is an important consideration for arboreal species such as Black Tree Monitor (V. beccarii).  Savannah Monitors (V. exanthematicus) and others that approach 5 feet in length need correspondingly larger quarters; modified cattle troughs are a useful option.

The 6-7 foot-long Nile, Lace, Crocodile and Water Monitors require room-sized enclosures with drainable pools.

Predator-proof outdoor cages are the ultimate in “luxury accommodations” (some folks use modified bird aviaries).  If a safe, escape-proof room is available, out-of-cage exercise time can make a real difference in your lizard’s quality of life.


Stout branches, wooden shelves and secure hide boxes should be arranged according to each species’ individual needs (please post questions below).  A water bowl large enough for bathing is essential; the aquatic Merten’s Monitor should be provided with a large swimming area.


Sand is suitable for Desert Monitors and others native to arid habitats, while cypress mulch works well for forest dwellers such as Green Tree Monitors (V. prasinus).  I’ve found Crocodile Monitors prone to foot abrasions when kept on concrete, and have since used rubber mats or rubber-coated floors for all large species.

Although impactions due to swallowed substrate are rare, food should be provided in large bowls or via tongs, so that ingestion is limited. 


Monitors need daily exposure to UVB light.  Use a high-output bulb, such as the Zoo Med 10.0, and position the basking site within 6-12 inches of it.  Mercury vapor and halogen bulbs broadcast UVB over greater distances and emit beneficial UVA radiation as well. 


Temperature should be maintained at a range of 79-85 F for most species.  Incandescent bulbs should be used to create a basking site.  While some do well with basking sites set at the more-or-less “standard” lizard temperatures of of 90-95 F, many monitors need to warm themselves to 120 F or even higher; please post below for details on individual species.  Ceramic heaters or red/black reptile “night bulbs” may be employed to provide heat after dark.  Under-tank heaters may be used to create a warm basking surface.

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.


Storr’s and Savanna Monitors, and other desert/grassland adapted species, develop health problems in damp enclosures, while rainforest dwellers such as Blue Tree Monitors (V. macraei) need access to humid and dry areas.


Males will fight savagely and cannot be housed together, and females sometimes battle for dominance.  Juveniles may get along, but they must be watched carefully. 


Green Tree MonitorStrict attention to diet is essential if you are to succeed with monitors. Nutritional deficiencies can develop quickly, and are difficult to treat.  High calcium intake and exposure to UVB light is especially important for young animals.

Small, largely insectivorous species (i.e. Blue and Green Tree Monitors) need a highly-varied diet comprised of roaches, crickets, butterworms, hornworms, super mealworms, wild-caught insects and other invertebrates; pink mice can be offered 1-2 times weekly. Canned snails and grasshoppers, and hard-boiled eggs, can be used to provide variety.

Nile Monitors and similar species fare well on mice and rats alone; whole freshwater fishes are an excellent rodent-alternative for Water and Merten’s Monitors.

Food (other than vertebrates) should be powdered with Tetra ReptoCal or Zoo Med ReptiCalcium.  Vitamin/mineral supplements such as Reptivite should be used 2-3 times weekly.



Further Reading

Range Information for all Species

Fruit-Eating Monitor, Red-Headed Monitor and Water Monitor Relatives discovered.

Monitor Lizards (notes on individual species)

Nile Monitor image referenced from wikipedia and originally posted by D. Gordon E. Robertson
Water Monitor image referenced from wikipedia and originally posted by Deror Avi


  1. avatar

    Hello Frank,
    I was interested to read this post, especially your remarks on the temps for Savanha monitors and
    that they develop health problems in damp enclosures.
    The reason being in even the up to date information in the UK, says there temps should be 110 some even say 120 which I myself think is high.
    Likewise current information often refers to spraying the enclosure, obviously not so it’s wet, is spraying not a good idea then, perhaps you could clarify these points for me please.
    The savanna we have at the rescue is between 4 to 7 months old, has not handled much and on the small size.
    Any advice is much appreciated.
    Have just found your blog tonight very informative thank you,

    • avatar

      Hello Bella,

      Thanks for the kind words. Savannah monitors occupy a huge natural range, with some populations being adapted to warmer conditions than others. However, a basking temp of 90-95F works well for all. While basking, the lizard will reach a higher temperature than the air around it, as the skin absorbs heat (i.e. I’ve measured 20F differences in air just above the shells of basking turtles, as compared to the shell itself, even on merely warm spring days). At 90-95 F, the lizard will be able to attain any body temp necessary by adjusting its time at the site. Even at 90F, it mat be hard to provide a thermal gradient unless the cage is very large, as the enclosure may take on the basking site temp. 110 or higher will do no harm if the lizard can move away, but it may be difficult to provide cooler areas.

      Spraying is fine, and beneficial, as long as the cage dries thoroughly within 30-60 min.

      Please let me know if you need further info, best, Frank

  2. avatar

    hello frank,
    Thank you for the information.
    I had noticed through research of my own albeit spasmodic and not under controlled conditions, the differences you noted in temperatures on air and body, whilst I recognice they will move away to a shadier or cooler spot, as you say it makes controlling temps more difficult, whilst I do have a large vivarium, it concerned me for others as well who do not realize the difference it can make, especially if they have no means of monitering, which now seems to be common place and way to small vivs, wich puts undue stress leading to illness much of which I see with rescues.
    We all of course have made mistakes and will still do so I am sure, how ever i’m rambling now and your a busy man.
    Any information you have is always welcome I love learning, research and looking after all kinds of beasties.

    So I will take my leave as I got so caught up in your writings that I didn’t get to bed till 3.30 am, but, it was extremely interesting and enjoyable.

    I am so glad you didn’t become a lawyer ,lol.
    Is any of your reasearch or books available in the UK, I would love to read them.

    Thank you so much for your time and ongoing works it makes a big difference to those reptiles not so lucky as to be looked after by you.

    Oh I almost forgot if you have any writings, research on Spiny Lizards especially S. Ponsettia, I would be very interested, not much seems to be known about them compared to other agamas.
    I have the basics right I believe, and one came into the rescue yesterday, another reason I was up all night.
    Thank you I will try to keep it short next time.
    Looking forward to hearing from you and thank you.
    Shall look you up on Facebook, My rescue page is on facebook too.

    • avatar

      Hu Bella,

      Thanks so much for the kind words and for the plug on your FB page; looks like you are doing some fine work. I’ve long been a licensed rehabber and nuisance wildlife control person as well, these days I stay with unusual/exotic anuimals (tigers showing up in NYC as pets, coyotes finding their way into Manhattan from suburbs, larger reptiles, et, My good friend runs Social Tees Animal rescue here, I help out when I can.

      Please don’t hesitate to write…this is what I do and enjoy; please elt me know if you have specific needs and I’ll send links or answer ques…blog search engine is not great (others take care of it for me) but I can easily send links to articles. let me know if you need any to use on your own sites, FB as well.

      Hand held temperature sensing guns are a great way to keep track of temps; I use in both home collections and zoos – point at a spot and you can quickly see basking temp, cool areas, heat leaks, etc…I’m trying to get my blog sponsor to carry them and market to reptile owners.

      Here are links to a 2 part article on swifts/spiny lizards http://bit.ly/bhNExn, http://bit.ly/bhNExn; just basics on care, but may interest you. They need lots of room, high UVB levels (high output bulb, basking site within 6-12 inches if a florescent), tend to be high strung, stress easily, highly varied diet important, the species you mention and most others are arid adapted, similar heat/dry requirements as we discussed re Savannahs.

      Thx for your interest in my books; I believe they are available via Amazon or otherwise in UK, but I don’t keep track as publishers take care of all that. I wrote 2 for the Barron’s pet care series, Newts and Salamanders and Seahorses, The Everything Aquarium Book (fish, FW and marine insects and other inverts, some amphibs), Leopard Geckos (Healthy Pet Series), and a few Knowledge Card Packets for the Sierra Club – Helping Animals (volunteer programs, backyard habitat, etc) and Why We need Insects, Spiders and other Inverts.

      Happy you are reading the articles; please post as often as you wish..great observations and very useful for readers from here and other countries to have comments from someone based in UK.

      Best regards, Frank

  3. avatar

    I felt it necessary to comment on the suggestion of 90-95 F basking temperatures for monitor lizards presented here. While these temperatures were once considered sufficient more than 15+ years ago when there was very little information available on the thermoregulatory habits of monitor lizards and when successful captive reproduction was infrequent.

    Since then, there has been a major paradigm shift in the way that monitors are kept, particularly regarding the range of temperatures offered to captives. Basking temperatures of over 45 C (115+ F) are now regularly offered to captives, with many species actively seeking out and basking at temperatures exceeding 150F when given the option.

    This paradigm shift is discussed in detail in a recent study to come out of the Bronx Zoo that I highly recommend:

    Mendyk, RW, AL Newton & M Baumer. 2012. A retrospective study of mortality in varanid lizards (Reptilia: Squamata: Varanidae) at the Bronx Zoo: Implications for Husbandry and Captive Management. Zoo Biology, DOI: 10.1002/zoo.21043

    A summary of the paper is available at:


    • avatar


      Thanks for the input; We have done well in general at the Bronx Zoo with the temperatures described; basking lizards can raise their body temps above that of the basking site; problems can arise if the animals are stressed/shy and do not bask as long as is necessary to achieve appropriate temps. I’m aware of the article you cited, but have not read it; it was published after my retirement. I do know that there were problems in some large exhibits that could not be heated adequately, or where shy individuals did not bask. Best, Frank

  4. avatar

    Hi Frank thank you for your information and your books, we have hand held sensing guns over here, they are much more expensive than in America though, only the dedicated over here tend to have them.
    Mind you most things reptile wise are cheaper in America, I have ordered before from your country but unfortunately our parcels can get opened at the port this end and they wacks lots of tax on the parcels making it rather off putting to shop in America, but you have many things we dont have here, such a shame.

    Thank you for the book list, may I say disgraceful, One Reptile Book, tut tut Frank, lol, better get writing.
    Links on research etc, would be wonderful, I can always use things for my sites, thank you.
    Retired Frank ?,

    Interesting to see that Varinid wrote about higher temps, will have to read the article he linked.

    I’m sure you will be writing an Autobiography on your life and works, if not ,why not.
    Take care, I will be writng often I’m sure.

    • avatar

      Hi Bella,

      I’ve heard about the price differences from others also. Well, we probably make up for it in rent/real estate costs, at least in Manhattan, anyway…beyond belief!

      I worked at the Bx Zoo for 21 years, left before retirement for freelance work, needed time for some other things as well. I consult for several zoos, aquariums and museums and write; have some good contacts for fieldwork, but research funding difficult; re the books – unfortunately, I need to stick with what I’m paid to write, and publishing is very tough these days. Luckily my interests are wide, and I’ve worked with every creature imaginable, so I’m usually able to find opportunities. Friend and family urge me to write an autobiography as well, but not possible unless I was assured of publication beforehand..time/money and all.

      I don’t know the author of that paper, he may have been a curatorial intern or something similar; it was based on several animals at the Bronx Zoo, not sure what temps were involved, or the status of other factors that can affect health. Higher temps can work…usually easier to provide in a zoo, due to exhibit size, ability to create temp gradient. The link may be to an abstract, Zoo Biology articles usually not available online other than by subscription.

      Let me know when you need articles – what subjects or species, and I’ll send what I have, best, Frank

  5. avatar

    “Hand held temperature sensing guns are a great way to keep track of temps; I use in both home collections and zoos – point at a spot and you can quickly see basking temp”

    I have done this frequently in areas with wild monitors (I live in Australia), frequently even aiming at a spot after seeing a monitor basking there. The basking temperatures used by monitors is much higher than 90-95F, especially as most species of monitor have been shown to have a preferred core body temperature of around 36C (98.6F).

    it has been shown that they will bask at much higher temperatures to attain their preferred core body temperature quickly. Otherwise they’d have to spend all day basking rather than foraging.

    The suggested surface basking temperature for most captive monitors is 120F and higher.

    • avatar

      Thanks for your input. Experience indicates Monitors basking at 90-95F can attain ideal core temperatures without basking all day, although, of course, not as quickly as when basking at 120 F. They will I’m sure choose to warm quickly in the wild, captivity is another matter; very high basking sites render it difficult to provide a temperature gradient. On the other hand, shy/stressed captive animals may not bask long enough to attain ideal core temperatures if they do not spend enough time at basking sites; a balancing act for keepers. I’ve been in touch with zoo/vet contacts working in this area, and will post additional information if appropriate, Best, Frank

About Frank Indiviglio

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Being born with a deep interest in animals might seem unfortunate for a native Bronxite , but my family encouraged my interest and the menagerie that sprung from it. Jobs with pet stores and importers had me caring for a fantastic assortment of reptiles and amphibians. After a detour as a lawyer, I was hired as a Bronx Zoo animal keeper and was soon caring for gharials, goliath frogs, king cobras and everything in-between. Research has taken me in pursuit of anacondas, Orinoco crocodiles and other animals in locales ranging from Venezuela’s llanos to Tortuguero’s beaches. Now, after 20+ years with the Bronx Zoo, I am a consultant for several zoos and museums. I have spent time in Japan, and often exchange ideas with zoologists there. I have written books on salamanders, geckos and other “herps”, discussed reptile-keeping on television and presented papers at conferences. A Master’s Degree in biology has led to teaching opportunities. My work puts me in contact with thousands of hobbyists keeping an array of pets. Without fail, I have learned much from them and hope, dear readers, that you will be generous in sharing your thoughts on this blog and web site. For a complete biography of my experience click here.
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