Home | Lizards | The Monitor Lizards (Family Varanidae) – Family Overview and Species Accounts, Part I

The Monitor Lizards (Family Varanidae) – Family Overview and Species Accounts, Part I

Introduction
Larry the Nile Monitor from Forgotten Friend Reptile SanctuaryHerpetologists and hobbyists alike have long known that there is something “different” about the family of lizards known collectively as “monitors” (or, in Australia, “goannas”).  One cannot observe a monitor for long without getting a sense of the animal’s intelligence – they scrutinize the world differently than do other reptiles, and their reactions to new situations are surprisingly quick and complex.  Recent studies have confirmed that monitors are unique, and, in many ways, the most intelligent and advanced of the lizards.

In years past pet keepers were limited to a very small number of monitor species from which to choose.  An explosion of interest in the group has radically changed that situation, and today animals rarely seen even in zoos are being commercially bred in huge numbers.  Happily, there are monitors even for those without much room – and the very smallest types still exhibit true monitor behavior, intelligence and “attitude”.

Today I’ll present an overview of the group as a whole.

Species Diversity
Sixty eight species of monitor lizards, all classified within the family Varanidae and the genus Varanus, range across Asia, Africa and Australia.  Although generally associated with warm climates, one species, the desert monitor (V. griseus) may be found as far north as Kazakhstan – at roughly the same latitude as southern Vermont.

In Australia, where over 2/3 of the world’s species are found, monitor lizards have evolved to fill a wide range of ecological roles held elsewhere by other lizards and by large, predatory birds and mammals.  Huge Australian species such as 8 foot long parentie monitor, V. giganteus, and the lace monitor, V. varius, are the dominant predators in their habitats,  as are Komodo dragons, V. komodoensis, on the islands of Komodo, Padav, Rinca and Flores.

At 8 inches long, the short-tailed monitor, or pygmy goanna,
V. brevicauda, is the smallest member of the group.  The infamous Komodo dragon is the world’s largest lizard.  It occasionally tops 10 feet in length, but is dwarfed by extinct monitor species which may have measured over 20 feet long.

General Physical Characteristics
Water Monitor Eating a FishAll monitors share a similar body plan – a long neck and relatively small head, sturdy body and limbs and a long, powerful tail, and most measure in the range of 2 to 5 feet in length.

The tongue is deeply forked and is flicked out repeatedly.  As with snakes, the tongue carries airborne chemical cues to the Jacobson’s organ, thus conveying information about the environment and other animals.

Male monitor lizards compete for females by grappling, often rising onto their hind legs during tests of strength.  All species lay eggs.

Diet
All monitors are alert, effective predators, with the various species taking an incredibly huge array of prey – termites and other insects, snails, spiders, crayfish and other invertebrates, birds and their eggs, frogs, turtles, snakes, hatchling crocodiles and other reptiles and amphibians, and rodents, weasels, tree kangaroos and other mammals to the size of adult deer.  Large monitors living near developed areas also prey upon domestic dogs, cats, chickens, ducks, pigs and goats, and consume carrion and offal as well.  The Philippine monitor lizard, or bataans (V. olivaceus), is unique in feeding upon fruit at certain times of the year.

On rare occasions, the Komodo dragons have attacked and killed people.  In fact, current restrictions on the long-held tradition of feeding goats to these huge lizards (a tourist attraction with possible links to local religious beliefs) is possibly at the root of the recent rise in attacks on people and livestock.

Habitats
Monitor lizards have evolved to occupy a wide variety of habitats – there are arboreal specialists, such as the green tree monitor, V. prasinus, aquatic species such as the mangrove monitor, V. indicus, and grassland dwellers such as the savanna monitor, V. exanthematicus.  There are also many generalists – Gould’s monitor, V. gouldii, a large lizard that occupies nearly all of Australia, is equally at home in grasslands, open forests, river valleys, cliff-sides, semi-deserts and nearly all other habitats within its huge range.

The Nile monitor, V. niloticus, is native to sub-Saharan Africa but is now thriving in southern Florida, where released pets have established breeding populations.  Approaching 7 feet in length, this aggressive predator is severely impacting the local ecology by out-competing and preying upon a wide variety of native species.

Wide-Ranging and Isolated Species
The size of the ranges of the different species varies greatly in extent.  For example, the blue tree monitor, V. macraei is limited in distribution to Batantan Island off Papua New Guinea while the 9 foot long Asian water monitor, V. salvator, is found from India through Bangladesh, Myanmar, southern China, Vietnam, Laos, Cambodia, Thailand, the Philippines, Malaysia and Indonesia.

Check back Friday for the conclusion of this article. And be on the lookout for more monitor articles in the future. Please let me know any feedback or comments you may have.

Frank

42 comments

  1. avatar

    Hi. I’ve got a Timor monitor, and have experience breeding chameleons. I’m looking to get a pair of Blue Tree monitors in an attempt to breed them. Can you point me in the direction of credible publications and sources on husbandry and breeding? I don’t want to get started until I know what I’m doing. Many thanks.

  2. avatar

    Hello, Frank Indiviglio here. Thanks for your interest in our blog.

    Unfortunately, there is not much work being done with this species in the US. A pair I worked with at the Staten Island Zoo in NYC was getting along well at the time; they have been together for over a year now… perhaps they have shown some interest in breeding. You can check in with the zoo staff re breeding attempts at:
    http://www.statenislandzoo.org/contact.asp

    A great resource for natural history information on all monitors, including notes on the original description of V. macraei, is the book Varanoid Lizards of the World (Pianka et al.). You can read the blue tree monitor entry on line at:
    http://books.google.com/books?id=0e3OuHRRoIQC&pg=PA212&lpg=PA212&dq=varanus+macraei+discovery&source=bl&ots=p7Wmf22wPl&sig=dy8huYlHrjqJmGixLhLJoZxOaD0&hl=en&sa=X&oi=book_result&resnum=1&ct=result

    A colleague forwarded me the following link, I have not checked but it contains various references, on of which deals with breeding this species (title but not content is on line):
    http://uts.cc.utexas.edu/~varanus/varanoidrefs.html

    European zoos have shown interest in this species…nothing currently on breeding that I could see, but you may wish to keep tabs on the World Association of Zoos:
    http://www.waza.org/home/index.php?main=home

    International Zoo News is a great resource for info on creatures not commonly kept in the USA. Back issues are on line – unfortunately, must search contents of each, as there is not a way, to my knowledge, of checking individual species’ entries:
    http://www.zoonews.ws/IZN/

    The following link from the Reptile Database (P. Uetz and the Zoological Museum of Hamburg) lists the best technical references for this species, perhaps one will provide useful resources re breeding:
    http://www.jcvi.org/reptiles/species.php?genus=Varanus&species=macraei

    Sorry I couldn’t be of more help, please let me know if anything useful turns up.

    Best regards, Frank Indiviglio.

  3. avatar

    We’ve got a copy of the book at the university library, so I’ll start there. Thanks much for the help, and I’ll let you know how things go. The pair I’m looking at has been cohabitating, but I wouldn’t want to breed them and risk the life of the female to being egg-bound, etc. Thanks again.

  4. avatar

    i have a peach throat monitor, and savannah monitor. I was wondering if it was possible to breed the two types, or any other monitor with one another?

  5. avatar

    Hello, Frank Indiviglio here. Thanks for your interest in our blog.

    A number of reptiles and amphibians of different species have interbred in captivity…such is especially common among horned frogs and the various rat snakes. Peach-throated and savannah monitors would not likely inter-breed, however, as, being from New Guinea and Africa respectively, they have evolved in isolation from one another for a long period of time. If they did reproduce, the young would likely be infertile, and possibly suffer developmental abnormalities.

    Hybridization is an interesting concept, but most biologists frown upon the practice. As we learn more and more about genetics, we are realizing that tiny differences in even very similar animals are important to preserve…once they are mixed with related animals, these unique characteristics can be lost, and newly formed traits take their place. Sometimes these spread very rapidly, either via captivity or through escaped/released animals, and serious problems result. For example, Caroline anoles (Anolis carolinensis) from north Florida have a greater tolerance for cold weather than those from south Fla. and the keys. In captivity, animals from both populations, as well as from Louisiana and elsewhere, have long interbred…this has likely drastically changed their abilities to survive in certain habitats, and could seriously jeopardize future captive release programs.

    Hybrids are also common in the tropical fish, bird and tarantula trades. Years ago zoo’s often produced hybrids to attract visitors…I remember seeing a “liger” (infertile tiger/lion hybrid) at the Bronx Zoo as a boy.

    Hybridization sometime occurs in the wild…it is a regular part of the reproductive cycle of some insects and fishes, but is otherwise rare. Surprisingly, a grey whale/blue whale hybrid and a grizzly bear/polar bear hybrid have been found in the wild – the reasons behind this are unknown.

    I hope this was useful…please let me know if you need further information. Breeding either species of monitor is a fascinating endeavor…I recommend you try if you have the space, and would be happy to provide some info.

    Best regards, Frank Indiviglio.

  6. avatar

    I have a Hybrid monitor lizard the guy that i bought her from told me that her dad is the really big monitor lizard and her mom was the more medium sized one….I would love to know what species she is..do you know?

  7. avatar

    Hello, Frank Indiviglio here.

    Thanks for your interest in our blog. Unfortunately, the are quite a few species of monitor that will inter-breed; no real way to tell without knowing the Latin names; not all require the same care, so it would be useful to get this information from the breeder. When you do, please write back if you need care and feeding information.

    Good luck and please keep me posted.

    Best regards, Frank Indiviglio.

  8. avatar

    I have experience with savannah monitors, but not many others, I am looking to get another monitor, something other than a savannah, what would you recommend as a good pet, docile behavior (relatively speaking), if you could point me in the right direction as a good one to purchase and raise, and where to get one.

  9. avatar

    Hello Cory, Frank Indiviglio here.

    Thanks for your interest in our blog. Please let me know how much space you have available, as that is a major limiting factor. I lean towards the smaller species, as it is easier to provide them with appropriately-sized enclosures…please write back and I’ll provide some ideas,

    Best regards, Frank Indiviglio.

  10. avatar

    I have an enclosure that is 12X8X6, huge space, I built it for one of my savannahs that I had years ago, I have upgraded it since, lots of room, good lighting, good heat, has a pool in it, just a little one

  11. avatar

    Hello Cory, Frank Indiviglio here.

    Glad to hear you have such a large enclosure; good thinking. I find it better to keep a small-moderate species in a large enclosure, rather than the largest species that can be accommodated. In this way you can see much more beahior, perhaps keep multiple animals, and in general provide for a better quality of life. Mangrove monitors come to mind – they need a large tub of water, however. Since you have 6 feet of height, my first choice would be a small arboreal species such as black or green tree monitors. You could house a male and 2 females, and add nesting boxes – I’ve bred both species in smaller enclosures than yours.

    Temperment varies a great deal among individuals, but the above and most others are more high strung than Savannahs in general. In a large enclosure, tree monitors especially tend to shy away from human contact; however, they more than make up for this by providing so much in the way of interest to observe.

    Good luck, enjoy and please keep me posted.

    Best regards, Frank Indiviglio.

  12. avatar

    well, I bought a Dumerils Monitor for the enclosure, friendly guy, enjoys interaction and free roaming, he is really a very nice lizard.

    I also bought a juvenile black throat at the same time, I house him in the spare room in my house, I have set up everything he needs, heat, light, dirt, tree, small pool, hiding spots, he is still shy and defensive, but he is already calming down and it has only been 2 days

  13. avatar

    Hello Cory,

    Thanks for the update…sounds like you are taking care to provide great habitats for your lizards. One thing to keep in mind with large enclosures is that the lizards should be able to get close to the UVB source – pairing the UVB bulb with a hot basking light helps attract them to it. In a room situation, you may need to enclose the fixtures in wire or otherwise prevent the lizards from having direct contact.

    Good luck and please keep me posted.

    Best regards, Frank Indiviglio.

  14. avatar

    I have already done that, they are in a separate enclosure with an open face, with a small water tub if he wants to dip while basking.

    Thanks for the tip.

  15. avatar

    Hello Cory,

    Thanks for the feedback – sounds ideal.

    Good luck, enjoy and please keep me posted on your progress.

    Best regards, Frank Indiviglio.

  16. avatar

    I WANTED TO KNOW IF A NILE MONITOR AND BLACK THROAT COULD BREED IF SO IF THE OFFSPRING WOULD BE OK

  17. avatar

    Hard to say, Branden…although placed in the same genus, they likely vary greatly in terms of genetics and mating behavior, given their evolutionary history. Argus and sand monitors will hybridize, I believe, but I don’t know of any other examples. then again, I never expected some of the whale and bear hybrids that have turned up recently, not to mention the snakes and turtles produced by hobbyists…

    Let me know if you turn up additional info, or have further questions, best, Frank

  18. avatar

    I WANTED TO KNOW BECAUSE I HAVE THE NILE AND A BLACK THROAT COMING AND I WANTED TO KNOW IF THEY WERE TO BREED WHAT TO EXPECT NOW I AM NOT LOOKING TO CREATE ANYTHING I JUST BROUGHT A MALE N FEMALE

  19. avatar

    Thanks for the feedback; best course is to keep them separated; in addition to aggression concerns, when mixing 2 related species there’s always the chance that a parasite/other micro-organism that is relatively harmless to one could cause serious illness in another. Best, Frank

  20. avatar

    I USE TO HAVE A LACE AND A CROC MONITOR THAT LIVED TOGETHER FOR 6YEARS INTO I HAD TO GIVE THEM TO MY BROTHER IN FL BUT THEY WERE ALSOME LIZARD AND I WANTED TO DO A NILE AND BLACK THROAT I HAVE A CAGE BUILT FOR THEM 11 FEET BY 6 FEET WIDE BY 7 FEET TALL

  21. avatar

    It can work but the points mentioned earlier are always a concern. In zoo exhibits we do not mix related species from different habitats or ranges. best, Frank

  22. avatar

    SO IF I KEEP THEM WELL FEED AND IN A CLEAN CAGE WITH GREAT HEAT ALSO GIVE THEM THE RIGHT VITAMINS THEY SHOULD BE OK

  23. avatar

    Not necessarily; sorry if I was unclear. Parasites, bacteria and other micro-organisms easily pass between related species. One species of Salmonella, for example, may cause few if any problems in one species but can be deadly in another (all reptiles should be assumed to be carrying Salmonella). Similar to what happens when tourists get sick after drinking tap water in a foreign country…germs within do not both locals, who have evolved an immunity. This may or may not happen, but it is one of the reasons for the zoo policy mentioned earlier.

    There is also no way to predict whether or not they will get along.

    Best, frank

  24. avatar

    SO IF I HAD TWO NILES IN ONE CAGE IT WOULD BE BETTER SEE WHAT I AM TRYING TO GET IS,THE NILE,CUBAN,AMERICAN AND SALT WATER CROCODILES CAN CROSS BREED BUT WHY NO MONITOR LIZARDS

  25. avatar

    That would be safer, but you’ll need to watch for aggression.

    A great many factors affect whether related species can inter-breed, and if the resulting young will be fertile (as in coyote-dog crosses) or sterile, as in horse-donkey crosses. In some cases, species that appear similar will have very different genetic make-ups, and be unable to cross. Yet some markedly different animals, i.e. lions and tigers, polar bears and brown bears, can interbreed. We know less about reptiles than birds and mammals, but crocodilians are not at all closely related to lizards, and so would likely not provide much useful info by way of comparison.

    On the bright side, there’s lots of room for interesting experimentation, and much to learn…

    best, frank

  26. avatar

    I UNDERSTAND .I LOVE THE MONITORS I AM GOING TO GET MY NILE N MY BLACK THROAT AND WATCH THEM CLOSELY

  27. avatar

    I hope all goes well and I look forward to your updates;

    Enjoy, Frank

  28. avatar

    I WILL UPDATE YOU AND POST PHOTOS WHAT WOULD U SAY IS A GREAT HIGH PROTEIN FOOD OR VITAMIN TO GIVE MONITORS

  29. avatar

    Both will do fine on mice or rats alone; supplements are not needed if whole animals are fed and they are provided high levels of UVB. please see this article for some further general care info (note: for these species, you can provide higher basking temps than I recommend there, up to 120F or so). Best, Frank

  30. avatar

    YES I HAVE 4 UVB LIGHT CERAMIC HEAT LAMPS AND 40GALLON WATER BEN AND A BIG DEN ON THE SIDE OF THAT TO GO IN AND COOL DOWN

  31. avatar

    Sounds good; be sure to check effective range of the UVB – how far they project UVB, so that you can set up basking site at right distance.

  32. avatar

    IT’S 18 INCHES ALSO I SEE YOU WERE WORKING AT THE BRONX ZOO ARE YOU FROM NY I LIVE IN MANHATTAN NY

  33. avatar

    IS IT BEST TO FEED LIVE OR FROZEN I ALWAYS FED LIVE TO MY LACE N CROC

  34. avatar

    Hello, yes, born and raised here; I left the zoo awhile back after 21 years, now consulting with several orgs and writing. Re diet, I never used live rodents …too many cases of bite wounds, even small ones, becoming infected in the past. Pre-killed or frozen works well.Best, Frank

  35. avatar

    Can you get your hands on two baby croc monitors .we should get together and share some ideas

  36. avatar

    Unfortunately I’m not in touch with any dealers right now. I’m bogged down with deadlines and set to leave for a short trip to Baltimore soon, but please stay in touch. The Bronx Zoo has recently rec’d a 2 young Komodos…not on display yet, but hopefully soon. Best, Frank

  37. avatar

    Hello Frank,

    I’ve been herping for about 15 years now. I have anoles, a Sudanese plated lizard, and a leopard gecko. I am interested in getting a monitor, and I’ve heard that ackies are a good place to start for beginners. Thoughts? Please send your comments to keelo804@gmail.com

  38. avatar

    Hello Keelo,

    I think these and other dwarf/small species are best for most home situations, regardless of experience. They have the same behaviors as the larger species, and it’s much easier to provide a suitably sized enclosure; in this way you’ll have a better chance of seeing a variety of behaviors, breeding etc. Even moderately sized monitors need far more room than most people can provide, lated lizard are a great species to work with also. A pair I kept in a huge exhibit at the Bx Zoo was still going strong in their late 20’s. Enjoy and pl let me know if you need anything, Frank

  39. avatar

    HEY BUDDY I AM BACK ON I WANTED TO KNOW ABOUT THE CUMING MONITOR I LOVE THE LOOK BUT DONT KNOW MUCH ABOUT THEM R THEY WATER MONITORS N DO THEY GET THE SAME SIZE ALSO ARE THEY SMART N LOVING LIKE THEM

  40. avatar

    Hi Branden,

    A very interesting species, only recognized as distinct in the last 5-6 years. Behavior, etc. appears to be similar to that of V. salvator, but they are not often kept so we have much to learn. All monitors seem to have advancedlearning abilities; reactions to people, captivity vary greatly – I’ve cared for several adult V. salvator that were quite difficult to work with, an all can change their behavior in response to stimuli that we cannot sense, so they must always be treated with caution. Here’s some info on range, classification. best, frank

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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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