Captive care of Monitors

This guide is used with kind permission of Daniel Bennett of Mampam Conservation. Please visit to learn more about the work this organisation do. Monitor lovers will find the butaan project of particular interest (Giant frugivorous monitor lizards that only live in the Philippines and are under serious threat from habitat destruction.). If you find this care guide usefull we urge you to visit the mampam website and make a contribution towards their great work.

Should I get a Monitor Lizard?    

Extract from A Little Book of Monitor Lizards © D. Bennett 1995. Viper Press, UK .

If you are new to monitor keeping and want to know which is the best species to keep you will find a mryiad of advice both online and in print on the subject. Most people would advise you to get something "easy" like a savanna monitor (Varanus exanthematicus). I strongly disagree. Hundreds of thousands of savanna monitors have been caught in the wild and exported to Europe and the US in the last decade, virtually all of which are dead within a year or so. Captive breeding of this species is practically non-existent. My observations of the species in the wild lead me to suspect it is a highly specialised feeder and the fact that so many are imported and so few breed lead me to believe that this animal is not suitable for people not well experienced in monitor husbandry. Admittedly it is a very tough animal and even in the worst conditions it takes a very long time to die, but this is not the same as being "easy to keep".

My advice is to get captive bred animals. I don't have anything to do with buying or selling monitor lizards and my commercial interests in the subject go no further than selling books and securing research grants. Therefore I'm not able to give advice about where to find captive bred animals so please don't bother asking. You will find contact details of monitor breeders elsewhere on the web. I would advise you to ask around and find suppliers with a good reputation. MANY people sell animals as captive bred that have actually been taken from the wild. As for which species, virtually any, as long as they are captive bred. Buying wild-caught monitors is a very dubious thing to do. They have the right to roam in the fresh air and sunshine and get cooked in soup and eaten by snakes, they should not end up dying very slow deaths in boxes. Catching wild animals for the pet trade involves hundreds of thousands of animals each year, virtually all of which die miserable deaths. I am sure that if the problem is not corrected soon it will result in extreme legislation that outlaws the keeping of many animals. But it doesn't have to be like that. What happens depends very largely on whether the animal buying public can behave responsibly. Buying creatures such as wild caught savanna monitors is not a responsible behaviour. Buy captive bred animals only, they will be much more rewarding and you can enjoy your animals without the guilt of being a destroyer of wildlife.

Wild caught, captive hatched, ranched and farmed Monitor Lizards - A Buyers' Guide

"Only the most cynical and desperate of poachers catch pregnant animals. In gravid monitor lizards the pet trade saw the opportunity to greatly reduce their overheads and fool their customers"

At a conservative estimate, 250,000 live monitor lizards are traded every year, all bound for the pet trade in North America, Europe and Japan. People who buy them are offered very little information about where their animals come from. Monitors in the pet trade are usually described as wild caught (WC), captive bred (CB), captive hatched (CH) or farmed. Wild caught and captive bred are self explanatory terms, but captive hatched, ranched and farmed are rather misleading terms which all mean the same thing.

Although captive breeding of monitor lizards has been revolutionised over the last ten years, the proportion of captive bred animals in the trade is still miniscule. This is because captive breeding has tended to concentrate on Australian species, with an emphasis on the dwarf (Odatria) species. It is virtually certain that any Australian monitor lizard offered for sale in Europe or North America will be truly captive bred. Commercial breeding of Asian and African monitor lizards, however, is still virtually non existent. If you find an African or Asian monitor lizard offered for sale as captive bred you should ascertain 1) if it has been bred in your country or abroad and 2) who has bred it. At present less than 1 in 10,000 of these animals are actually bred in captivity.

In recent years a large proportion of imported monitor lizards have been sold as captive hatched or farmed. This means that instead of capturing large numbers of individual lizards for export, only gravid females are collected. They are kept in captivity until they produce eggs, which are incubated artificially. The females are then "returned to the wild". This gives the impression of being more sustainable and ecologically friendly than dealing in wild caught animals, but in fact the opposite is true.

Adult female monitor lizards are extremely difficult to find outside the breeding season (typically we catch 6 - 10 adult males for every female we encounter). They appear to limit their movements to searching for food and accumulating energy to produce eggs. During the breeding season the females become extremely active as they search for good nesting sites. At this time of year they are easy to collect. The animals are kept in captivity, often in very unsanitary conditions, until they produce eggs which are then incubated artificially. As soon as they hatch they can be exported as extremely cute babies, not taken from the wild but "captive hatched" from mothers "released into the wild". In fact these animals, now exhausted and stressed, are almost guaranteed to perish. There is little incentive for the "farmer" to actually return them. It would be impractical to take each one back to the place it was caught, and more often than not the lizards are either recycled into the pet trade, sold for meat and skin or just dumped at a roadside. In a few cases (such as in Ghana) government departments collect the animals from different exporters and release thousands of them at a time. There is no evidence that any of these animal have ever survived to breed the following year. In countries such as Indonesia, where the females have been brought by boat from some distant island, death is inevitable.

Only the most cynical and desperate of poachers catch pregnant animals. In most hunting societies they are the only animals afforded protection, because without them the population will decline. However, the pet trade saw in gravid monitor lizards the opportunity to greatly reduce their overheads and fool their customers into thinking that their animals were collected "with conservation in mind".

As well as producing extremely marketable animals, ranching also allows for massive increases in profit. The rancher buys only a tiny fraction of the animals he needed before, so instead of buying, say10,000 animals, he pays for just 400. The unit price is thus reduced by over 95%! The importers may well be aware that unsuspecting people will be more likely to buy an animal that has not been collected from the wild, and may even be prepared to pay a few dollars more. In countries that have adopted ranching methods the number of people employed in the trade has dropped substantially (by over 60% in six years in Ghana). The remaining collectors tend to be among the most economically deprived people of their communities. Because there is so little money to be made from the trade in monitor lizards they sometimes resort to hunting more profitable animals. In recent years people I know have started to collect very dangerous (e.g. green mamba) and endangered animals (e.g. Mali giant tortoises)

Photo by Hans Jacobs

In fact buying wild caught monitors is a much more ecologically sound strategy. My experiments with the savannah monitor Varanus exanthematicus in Ghana show that about a third of the juvenile population is removed when a group of experienced lizard collectors visit an area, whilst the reproductive population is left undisturbed (Bennett, D. 2000. The density and abundance of juvenile Varanus exanthematicus (Sauria: Varanidae) in the coastal plain of Ghana. Amphibia-Reptilia. 21:301-306). Enough youngsters remain to ensure some survivors and I am sure that the exploitation had minimal impact on the population overall. In contrast when adult females are targeted it is inconceivable that the population would not be affected. Instead of a third of the youngsters being removed, entire clutches are taken and the adult females eliminated permanently.

If traders offer you captive hatched, farmed or ranched animals ask them if they understand how the process works. It is possible that they do. Unfortunately I don't know what they think. I have been investigating trade in monitor lizards in many countries since 1994. But although animal exporters around the world have always been happy to help us, no animal importers in North America, Europe or Japan have ever offered to cooperate.

Keeping Monitor Lizards successfully

The following chapters are dedicated to keeping monitor lizards successfully in captivity. "Successfully" does not mean that the animals merely live a disease-free existence until old age causes their ultimate demise. It means that all the functions of life are performed by the animals as they would be in nature, including reproduction. In my opinion, it is irresponsible to keep wild animals such as monitor lizards in captivity without at least attempting to breed them. Whilst keeping monitors alive in captivity, though not always an easy task, is one that is quite often accomplished, getting them to breed is still a rare occurrence and as such, it is the ultimate challenge to all keepers of these magnificent creatures.

According to CITES figures, trade in a minimum of 55,775 live monitor lizards was reported between 1975 and 1986. Between 1987 and 1993 the figure rose to over 270,000. This figure is probably a gross underestimate of the true numbers involved, but is nevertheless minuscule when compared with the Centre's figures for monitor skin and by-products (see Chapter 5). Unfortunately, the vast majority of live monitors exported to foreign countries fare no better than those exported as leather. Many die lingering deaths in enclosures that are neither large nor warm enough. Many people find such treatment of wild animals to be as repugnant as slaughtering them for their skins. They have no control over the fate of animals in Africa or Asia, but they campaign actively at home to stop the sale of exotic animals as pets, or even to outlaw the keeping of wild animals in captivity altogether. They argue that as well as being cruel the practise depletes wild populations, increases the risk of exotic escapees becoming established and, when species perceived as being dangerous are involved, poses a threat to the general public.

Their case is supported by a few unfortunate cases of foolishness and significantly more cases of neglect. As far as monitor lizards are concerned, none of the species traded in large numbers appear to be under any threat, real or potential, from the CITES regulated wildlife trade. Live specimens account for less than 1% of the overall trade of animals and products made from them. It is true that an unacceptable number of specimens fare badly in captivity. This can be attributed to ignorance due to a lack of available information about their way of life in the wild and their care in captivity. The trade in live monitors creates small numbers of reliable jobs in some of the poorest parts of the world. It also has the potential to greatly facilitate studies of the animals in the wild. Thanks largely to the efforts of a few pioneers, it has been established that it is quite possible to breed monitor lizards in captivity providing a few basic criteria are met. There is still a great deal to be learned however and the threat of legislation that will prevent further progress is very real in many places.

The purpose of this book is to bridge the gap between general guides to the care of reptiles in captivity and detailed guides to the captive propagation of monitor lizards that, as yet, appear not to exist. What follows is based entirely upon my own opinions and many, more authoritative, readers may disagree with some of my comments.

Monitor Lizards & International Law

Nearly all countries are signatories of the CITES convention which controls the trade in animals and plants considered to be vulnerable to commercial exploitation. All species of monitor lizard are afforded protection under this legislation. It is not lawful to transport the animals across international boundaries without a CITES export certificate from the country of origin and a CITES import certificate from the country of destination. In order to obtain these certificates you must satisfy the authorities that the animals are in your possession legally. Commercial trade in species listed on Appendix I of the CITES regulations is totally outlawed and permits only given for their export and import for other purposes under exceptional circumstances.

Five Asian monitor lizards are included on Appendix I: the Komodo Dragon, Gray's monitor, the Bengal monitor, the Caspian monitor and the yellow monitor. All other species are listed in Appendix II. Commercial trade is allowed, but all specimens must carry CITES documentation. Failure to comply with CITES regulations results in automatic confiscation of the animals and punishments ranging from fines to imprisonment. Buyers of monitor lizards should always get a copy of the CITES import certificate authorising their import. If the lizards subsequently breed and you want to sell the youngsters abroad you will be expected to prove that they are captive bred and that the parent animals were legally imported. Some countries, notably Australia, only rarely issue export permits for wild animals and never for commercial trade (however see Hoser (1993b) for a fascinating account of the illicit trade in Australian wildlife). Goannas reach the rest of the world either for research and breeding exchanges between institutions, or illicitly. Luckily many specimens are intercepted at borders and passed on by the authorities to zoos and individuals who succeed in breeding them. Captive born Australian monitors with CITES certification fetch very high prices. In addition to CITES regulations local laws may impose separate restrictions or even prohibitions on the import and keeping of certain monitor lizards.

Monitors as Pets

The Shorter Oxford English Dictionary defines a pet as "any animal that is domesticated or tamed and kept as a favourite, or treated with fondness". Monitor lizards can certainly not be domesticated. If you allow one the run of your home it will cause untold damage without showing the slightest remorse. If you let it out of the house it is highly unlikely that it will ever come back of its own accord. They can be tamed in as much as some individuals will eventually learn to tolerate gentle handling without showing aggression (especially when deprived of sunshine and fresh air), but expecting them to obey any commands, or show the slightest affinity for anything but other monitor lizards is unreasonable. Monitor lizards are ancient, intelligent and beautiful creatures capable of living "happily" in captivity for many years, but to describe them as pet animals would be misleading.

Monitor lizards survive by catching, killing and defending themselves against other animals. Therefore they are equipped with sharp teeth, strong jaws and powerful claws. Only adults of a few, very large, species have the potential to inflict serious injuries on people but all monitors can inflict scarring wounds and they should always be treated with caution. The most common wounds inflicted by monitor lizards are scratches to wrists and forearms whilst the animals are being handled. The tail is used as a whip in defence and can be mobilised with great speed and force. But the jaws are of the greatest concern. They sink through flesh to the bone and then shake with all their might.

Handling wild animals is not something you can learn from a book. Herpetological societies always have members who are happy to share their expertise. Wild monitors should not be handled without a pair of stout gloves that afford protection to the wrists. They should be seized from above by grabbing the back of the head and the base of the tail in one movement, so that the lizards cannot turn to bite. Obviously very large specimens should be restrained with a noose and require more than one person to lift them. Lifting the lizards by the tail is a very bad practise that can result in injury to either party. Animals kept inside are often much more docile than those kept in open air. Ditmars (1910) records an incident in which some very docile water monitors were moved outside for the summer whereupon they immediately reverted to their wild state, attacking their keeper at every opportunity. Once deprived of fresh air and sunshine they soon became placid and friendly again.

"Taming" Monitors

Well-kept monitor lizards do not require any grooming. If their toenails become too long and need to be cut this should be taken as an indication that the furnishings in the enclosure are unsuitable. Dead skin should come off of its own accord. If it needs to be pulled off this indicates that some environmental parameter (probably humidity) is incorrect. Some of the people who have had most success with breeding monitor lizards consider it important that the animals do not get used to being handled and are allowed plenty of privacy. One obvious reason for this is that monitor lizards show their dominance to weaker individuals by rubbing their backs or lying on top of them. A monitor lizard that is handled in this way assumes the role of a subordinate animal and may be less likely to initiate or respond to courtship. However, in the family environment the lizard keeper may feel that it is in their interests that the lizards tolerate gentle handling by themselves, their parents or their children. The irrational fear of reptiles experienced by many unfortunate people often vanishes when they touch one and realise that it is warm and dry rather than slimy and cold. When monitor lizards are used to being handled they are much less inclined to struggle and bite. Individuals used to humanity from a early age are sometimes extremely docile. The process of taming some monitor species is neither dangerous nor difficult if the animals are obtained as juveniles. Individual monitor lizards have very different temperaments and many will become placid, almost friendly, in human company. However is not a total guarantee of safety, and large specimens should be treated with caution at all times, regardless of their disposition. The monitor keeper who is admitted to hospital as a result of his or her carelessness does little to enhance the popular perception of reptiles.

To tame a monitor lizard it should be handled regularly. Wash your hands to remove all scents that might be interpreted as edible and hold the monitor firmly. It will struggle at first, but should eventually settle down. Some monitors enjoy being scratched gently; under the chin, above the eyes, and particularly behind the ear. They almost seem to show their pleasure by closing the eyes and breathing deeply. After a while one gets used to a particular monitor's erogenous zones and the taming process becomes easier. There is a sensation associated with tickling an enormous water monitor under the chin that is difficult to describe! If they do get annoyed they will usually give ample warning by hissing and inflating the throat before resorting to violence. In this case, leave them for a day and try again. Never handle a monitor while it is digesting large meals and never attempt to tame large animals unaccustomed to people. The more they are handled as youngsters, the tamer they will be as adults, but it is important to continue to handle the monitor regularly throughout its life, lest it forgets. Very large monitor lizards have the potential to inflict horrendous injuries and they should always be treated with caution. All monitors react to smell, and approaching a large male whilst bearing the scent of a rival could give you more than you bargained for.

How much space do they need?

A myth, that is extraordinarily common considering its stupidity, is that an animal "will grow to the size of its surroundings, and then stop"! This, of course, is utter nonsense. A healthy reptile never stops growing, from the day it is laid to the day it dies. Many monitor lizards spend most of the day fast asleep, and may not initially appear to very active animals. However when they do move they tend to cover a lot of distance. Typical daily forays for even dwarf monitors may be in excess of 200m per day and many monitors typically walk several kilometres in an afternoon. Obviously it is not possible to provide this amount of space for captives and it has been demonstrated that many species will do well in remarkably small enclosures. The term "small" is relative however. Captive lizards become lethargic in cramped surroundings for several reasons:

  1. Thermoregulatory behaviour. Normal lizard behaviour involves movement from areas of one temperature to a warmer or cooler environment in order to maintain a preferred body temperature. In small enclosures the temperature is uniform and the lizards cannot alter their body temperatures significantly by moving. A large enclosure, on the other hand, may contain a range of temperatures, from 18-44oC for example. This gives the lizards the opportunity to select a body temperature that suits them and alter it at will. A small enclosure heated to 44oC would kill the inhabitants very rapidly.
  2. Foraging. Monitor lizards do not swallow huge meals and then go to sleep for six months. They spend most of their active time searching for food; in leaf litter, under cow dung, underwater, on the branches of trees, in burrows, termite mounds, rock crevices, abandoned buildings etc., usually finding only small invertebrates. They also learn very quickly and a monitor kept in a small space quickly realises that there is nothing worth foraging for and stops looking. Larger, well-planned enclosures may always contain concealed food items and promote more normal activity patterns.

Prospective purchasers of a baby water monitor usually fail to comprehend that the little brightly-coloured lizard in the pet shop will soon grow into a formidable carnivore somewhere between two and three metres long and quite capable of putting its owner into hospital should it feel thus inclined. There is no reason why these animals should not be kept safely and successfully if their basic needs are met, and space is of primary importance. Large terrariums are inconvenient because of the space they take up and can be expensive to keep warm. Nevertheless with careful planning they can be made unobtrusive and costs can be minimised. In the accounts of monitor lizard species given in Chapter 6 I have cited the smallest known enclosure in which the animals are known to have reproduced. A few of them are impossibly big and relate to animals kept outside in the tropics but most are a reasonable size.

A general rule for the larger species (i.e. those not belonging to the subgenus Odatria - see Chapter 2) is that the enclosure should be at least three times as long and twice as wide as the total length of the lizard at maximum size, measured from the tip of the tail to the tip of the snout. This allows them at least moderate space in which to move. An adult trio can be housed in enclosures of these sizes so long as ample basking and hiding places are provided. Arboreal species also need to be provided with a tall enclosure that allows them to climb at least their own body length above the ground. Monitor lizards grow so quickly that it is usually not sensible to have to build successively bigger enclosures as they increase in size. Dwarf monitors appear to need much less space than their larger counterparts. Many will live long lives in areas of less than 1m2 if adequate furnishings are provided.

If space really is a problem, and the unfortunate creature is already in your possession, then it is better to try to tame the animal and give it the run of the house rather than keep it in a cramped terrarium. As long as they are provided with a suitable source of heat they should regulate their behaviour around keeping warm. Some monitors continually seek out the coldest parts of a room and lie there immobile for days or weeks. I presume that this is related to the need for an annual period of inactivity. Often they will conceal themselves somewhere that makes them very difficult to retrieve. It would be very foolish to allow a large untamed monitor lizard to wander about the house. Even tame ones will destroy your furniture.

Food & Supplements

No expense should be spared when raising animals destined to be fed to monitor lizards. They should be fed only fresh foods and kept under the best conditions possible. For guidance on breeding insects, rodents, snails and other suitable prey items you should consult members of your local herpetological society. With the exception of Gray's monitor (whose diet in captivity is discussed in Chapter 6), plants do not figure in the diets of monitor lizards.

Vitamins and Minerals
The regular use of good vitamin and mineral supplements is indispensable. Feeding monitors on a varied diet should, in theory, provide all the nutrients, vitamins and minerals required for good growth and health. But vitamin and mineral deficiencies are very common in captive monitor lizards, even when they are housed under ideal conditions and their prey animals are reared on ambrosial fodder. Horn & Visser (1990) suggest that monitor lizards increase their mineral input by rubbing their prey into the ground before consuming it. All food items should contain supplements and many people find the use of soluble vitamins in drinking water to be advantageous. Invertebrates can be dusted with vitamin and mineral powders whilst dead vertebrates can be injected with liquid supplements. The micro-nutritional requirements of reptiles are complex and beyond the scope of this work (an excellent discussion of the subject can doubtless be found in Frye (1991). A surfeit of certain vitamins (particularly A and D3) and minerals are known to cause problems, but in general monitor lizards are not prone to health problems associated with the overuse of supplements, providing suitable ones are chosen. A bewildering variety of vitamin and mineral supplements are available, many made specially for reptiles and all containing slightly different proportions of different micronutrients. Balance between calcium and phosphorus is particularly important. The most authoritative works on breeding monitor lizards in captivity recommend the use of vitamin and mineral supplements with all food items and suggest the use of a calcium:phosphorus ratio of 2:1. (Horn & Visser 1990; Eidenmuller 1992).

Insects make up the most important part of the diet of many monitors in the wild and should form the staple diet of most species in captivity. Their movements trigger the monitors' predatory natures and because they are difficult to catch they make the lizards work for their food, sometimes the only exercise lethargic specimens ever have. Crickets, locusts, grasshoppers, cicadas, butterflies, moths, beetles, cockroaches, mantids, stick insects, maggots, June bugs and beetles will be accepted by many monitors. Some of these foods can be cultured but many suitable insects will be available locally at different times of year. When foods are collected from the wild you should ensure that they have not been exposed to pesticides and that you are not collecting protected species. Monitor lizards can eat large amounts of insects in a single meal which would be impossible to collect outside in any season. They can be bought locally or obtained by mail order but the cheapest and most reliable option is usually to breed them at home. Many initial attempts at breeding crickets result in mass escapes that make further attempts impossible due to household hostility. If the crickets escape outside during warm weather they may serenade the neighbourhood for the rest of the summer. Therefore, colonies should be housed in a very deep, smooth sided containers and kept well covered. One of the best orthopterans to breed for monitor lizards is the black cricket, Gryllus bimaculatus. Unfortunately its song is not as melodic as that of the less nutritious members of its family, but it is a large meaty insect that few lizards can resist. Many exotic invertebrates are available through the post from entomological suppliers and a few of them may be inexpensive enough for occasional inclusion in the diet. An excellent food for monitor lizards is the Argentinean wood cockroach (Blabtica dubia). They reach a large size (adults can weigh up to 5g) and are easy to keep and breed (providing the temperature never falls below 18oC). Although considered unsightly by many people, this large insect cannot fly, nor can it climb smooth surfaces, making escapes unlikely. They can be obtained from entomological suppliers, or from other reptile keepers.

There is little or no danger of introducing disease with insect prey (although they are known to act as vectors of disease in wild monitors (e.g. Mackerras 1962)), but many insects and invertebrates are poisonous to some animals, and so their use should be avoided. They include centipedes, millipedes, scorpions, spiders, and many insect larvae. Although all these creatures are preyed upon in the wild there is no guarantee that monitors are immune to the poisons of alien species. All invertebrate prey should be dusted with a vitamin and mineral supplement just before they are fed to the monitors.

Other invertebrates
A wide variety of land and water dwelling molluscs and crustaceans are devoured with relish by many monitors. With the possible exception of the slugs and snails none can be propagated, so they must be bought or collected. Slugs, snails, crabs and crayfish can often be found locally. More exotic species such as giant African land snails and hermit crabs are available from some pet shops. The shells of molluscs and crustaceans present no difficulties to monitor lizards. Small prey are swallowed intact whilst the larger ones are crushed and their shells discarded or swallowed separately. Saltwater crabs and molluscs should only be offered to lizards that are known to eat marine organisms in the wild and can therefore tolerate high salt intake. Earthworms make a good food for many monitors and are very easy to collect.

Rodents, rabbits and other mammals make excellent foods for most monitors lizards, but they should not be used to the exclusion of other prey types. Domestic varieties of many mammals are inexpensive, widely available and very easy to breed. However, some insectivorous and molluscivorous monitors seem unable to cope with large amounts of fur in their diets and their use as food for these species should be restricted to the occasional treat. Mammals should be fed sparingly to all monitor lizards because if overused it may be difficult to get them to accept the other foods essential to their health. Very small monitor lizards can be offered chopped up portions of baby rodents.

Reptile keepers have a bad reputation with rodent keepers, and it appears that the latter rarely impart their knowledge to the former. Mice and rats will live anywhere and eat almost anything, but those destined to become reptile food should be treated with particular compassion. They should be given sufficient space, kept clean and warm, and fed on the finest foods available. Even then their corpses should be injected with vitamin supplements just prior to use. Frozen rodents can be bought in bulk from some biological suppliers and thawed out when required but is unwise to use animals that have been frozen for over six weeks as food and, if available, freshly killed foods are always to be preferred. Night time walks down country roads often yield an abundance of fresh car victims. They make perfectly acceptable foods as long as there is no danger that the animals have been exposed to poisons. Using live mammals to feed monitor lizards is probably unnecessary, because the lizards "kill" dead food before swallowing it and therefore seem unable to tell the difference. Furthermore there is always the chance of an indignant rat biting back and causing serious injuries.

Birds and their Eggs
Most monitors will eat birds, ranging in size from day-old budgerigars to adult ducks and chickens. They should not be collected from the wild, but obtained through hatcheries, bird breeders or butchers. Vitamin and mineral supplements should be injected into the body cavity of dead prey animals before they are given to the lizards. Eggs make a good occasional food for many monitor lizards. Smaller specimens may crack the shells and let the contents run down their throats, whilst larger ones will swallow them whole. There is some danger of Salmonella infections with many farmed eggs which can be eliminated by boiling them until the yolks set, although this doubtless compromises their nutritional value.

Many monitors, including those not normally thought of as aquatic, are very partial to fishes. Many species of fish from the fishmonger are suitable as occasional foods for monitor lizards known to feed around seashores. They include trout, whitebait, herrings and mackerel. Freshwater fishes (such as goldfish and tropical species such as cichlids, barbs and rainbowfish) can be fed to all monitor lizards. Fish with sharp spines (which are often invisible) are unsuitable because they are adept at lodging themselves in their predators' throats. Livebearing fish such as platys and swordtails are ideal, because they are easy to keep and breed at home.

Reptiles and Amphibians
Although monitors eat many reptiles and amphibians in their natural environments, wildcaught animals cannot be recommended as food for captive varanids because of the very real possibility of disease transmission. On the other hand frogs, lizards and snakes which have been bred in captivity make good food, so long as they are known to be disease free. In practise it may prove very difficult to obtain sufficient quantities of animals to forma regular part of the monitors' diets. The best amphibians for use as monitor food are the frogs of the genus Rana, especially the European common frog (Rana temporiaria) and the north America bullfrog (R. catesbeiana). Both of these animals can be easily propagated and are extremely prolific. Although some monitors are known to prey on toads, the toxins of unfamiliar species may prove fatal, so they are not a suitable food. The same applies to a few frogs. Both the yellow monitor and the rough-necked monitor are known to eat amphibian eggs in the wild, but whether they would do so in captivity is unknown. Turtles and their eggs are eaten with great enthusiasm by monitors in the wild, but because of the dangers of amoebic infections they cannot be recommended as food for captives. All lizards and snakes will be eaten by monitor lizards. Certain species of geckoes, skinks, anoles and garter snakes are available at low prices, so captive bred specimens are readily available. However the dangers of passing on disease by introducing unquarantined reptiles and amphibians (dead or alive) into the monitor enclosure cannot be overestimated and only animals known to be free from disease should be used..

Unsuitable Foods
Monitors should be fed whole fresh animals whenever possible. Processed meats, offal and meat derivatives such as mince and dogfood are very poor and messy substitutes for the real thing. Great care must be taken to ensure that the monitor lizards do not eat food animals that have been treated with pesticides or other hazardous chemicals. Animals that appear sick or wasted should not be offered. Poor quality, intensively farmed foods (particularly birds and their eggs) pose a risk of Salmonella and other food poisonings. Some processed foods are sold specifically for feeding to carnivorous lizards, but I am unaware of any reports of captive breeding in monitors maintained on such a diet.

Disease & Choosing a Monitor

Unfortunately, the diseases of monitor lizards are many and the cures are few (Kohler 1992; Stanfill 1995). The good news is that once an imported monitor is cleared of disease, it should be possible to keep it that way by keeping its enclosure and furnishings clean and avoiding any contact with sources of contamination such as wild foods and other reptiles whose health is suspect or unknown. The bad news is that wild-caught monitor lizards always harbour parasites that have the potential to destroy their host, especially when they have been subjected to the stress of capture and shipment. For this reason all new monitors should be carefully quarantined until they are determined to be free from disease. This means keeping them in a separate room in a regularly sterilised enclosure used solely for this purpose. These organisms need to be identified and destroyed by a qualified vet. The presence of most serious parasites can be identified from samples of blood and faeces and are treated with a variety of drugs. Obviously it would be very foolish to attempt to diagnose and treat the diseases of tropical reptiles without professional help. More and more vets are developing an interest in exotic wildlife and most herpetological societies or zoos will recommend a specialist. Vets are very well trained and in the best position to diagnose disease and prescribe cures but it may be necessary to haggle hard over their fees. The use of do-it-yourself guides to the diagnosis and cure of reptile diseases cannot be recommended.

Until animals have been pronounced free from infection by the vet they should be isolated from all other animals. Clinical standards of hygiene are required in the quarantine enclosure. It should be well isolated from all other terrariums and only contain furnishings that can be sterilised. In all other respects it should be designed in the same manner as other terrariums and the lizards supplied with adequate space. light, heat, food, hiding places etc. Newly imported monitor lizards are often particularly nervous and this stress further weakens their ability to withstand disease. As far a possible the animals should be left undisturbed.

Careful quarantine and early elimination of potential pathogens by an expert is the key to keeping monitor lizards healthy. Thereafter they should remain healthy providing that their basic needs (good diet, correct temperatures and humidity, freedom from stress) are met and they are not exposed to infection from other reptiles whose health is suspect. A study of cause of death in 248 monitor lizards concluded that almost half had died as the result of infections (Kohler 1988). Whenever a monitor lizards appears to be ill it should be isolated immediately and the advice of an vet obtained without delay.

As well as internal parasites monitors are host to a many external parasites that attach themselves to the lizards' skins and suck their juices. Some lizard ticks are very beautiful and their ecology is fascinating (e.g. Hesse 1985, Auffenberg & Auffenberg 1990), but in captivity they must be regarded solely as vectors of disease. They should be dabbed with alcohol and removed with tweezers, taking care not to pull off the bodies and leave the mouthparts embedded in the lizard. If ticks spread to other lizards it may be necessary to destroy them with insecticides, for which veterinary advice should be obtained.

Obviously it makes sense only to buy healthy animals in the first place. Obtaining young captive bred animals is ideal, but at present wild caught specimens are usually the only available option for most species. As in all walks of life there are a number of disreputable characters who are not adverse to selling animals which they know have no chance of survival. Again, members of your local herpetological society will probably be happy to pinpoint the rogue dealers and recommend those that are honest and conscientious. Purchasing animals without seeing them first is asking for trouble unless you are buying them from a dealer whose reputation is unblemished. No matter how honest your supplier, inevitably some species of monitor lizard are very heavily infested with parasites when they arrive at their final destination. Most have the potential to survive for long periods in captivity if they are still strong and receive immediate veterinary care, but most untreated specimens are doomed within weeks, and Doctor Dolittle himself would be unable to save them.

When buying a monitor lizard it should be examined very carefully. Particular points to look for include;

An animal offered for sale which shows any untoward symptoms should be refused. Sadly, once monitor lizards have succumbed to infections they do not often recover. It is much better to leave them to die in the shop than to buy them and encourage the proprietor to get more. Wise dealers have monitor lizards screened for major parasites as soon as they are imported, and add the bill to the animals' price. Even so they should still be subjected to a normal period of quarantine after purchase.

Sexing Monitor Lizards

Obviously in order to attempt to breed monitor lizards it is necessary to have at least one male and one female. Unfortunately they are notoriously difficult animals to sex. In a few dwarf species males have spines at the sides of the vent which are only weakly developed or absent in females, but in at least one species (Storr's goanna) the spines are present in both sexes. Sex determination by differing scale characteristics around the vent has been described for the Komodo dragon and the Bengal monitor (Auffenberg 1981, Yadov & Rana 1988). In both of these species and many others males are reported to grow larger than females and the males of many African and Asian species develop bulbous snouts towards old age. These phenomena are of little practical use when trying to determine the sexes of wild caught animals whose ages are unknown, because obviously a four year old female will be larger than a two year old male. The males of some species are said to have wider heads or thicker tail bases than the females and although there is no reason to doubt this, such criteria are of limited use when animals from different locations and of unknown age are concerned.

Sex of monitor lizards is often determined on the basis of hemipenal eversion (notably in field studies in which the animals are not sacrificed). Wild animals unaccustomed to being handled often evert their hemipenes when being manipulated. If the hemipenes are totally everted then the animal is considered a male. But if eversion is only partial it is impossible to distinguish the male hemipenes from the similar structures everted by the females*, unless equipped with a very good knowledge of the differences in their morphology.

Furthermore, an animal that does not evert its hemipenes cannot definitely be considered a female. It might be an uncooperative or not particularly well endowed male. Immature animals do not evert their hemipenes and once the lizards have been handled a few times they generally stop displaying this behaviour. Acclimatised adults can sometimes be induced to evert their sex organs by spraying the vent with tepid water; otherwise hold the monitor upside down, push the tail down and apply gentle rolling pressure with the thumb over the vent, from back to front. Again, this may serve to determine the sex of some males with certainty but great caution must be exercised when interpreting the results from animals that fail to evert completely.

A number of more intrusive methods to detect hemipenes have been devised. A common method, used to sex many reptiles, is to probe very gently inside the vent with a lubricated, blunt, metal instrument (Honneger 1978). In theory, the probe will extend further in males than in females. The problems with this method are that most monitor lizards are too strong to allow the probes to be inserted without risk of damage, many females probe almost as deeply as males and the lizards appear to find the process extremely unpleasant. This is a method that can only be learned by direct observation of someone with experience. Other methods that are designed to forcibly evert the hemipenes require professional expertise (e.g. Balsai 1992). In general it is best not to interfere with the genitals of your lizards.

Another method is to use x-rays to detect mineralisation in the hemipenes (Shea & Reddacliff 1986, Card & Kluge 1995). A vet can do this by rinsing the vent with a barium solution or dye and taking an image at about 57.5kV, 125mA for 0.04 seconds or 40kV, 25mA for 0.6 seconds. This method has been shown to be effective in many species but not in Bosc's, Bengal, grey, Mertens', Nile, rough-necked, water and Timor monitors. Nor does it work with young animals. Also it is not clear from the literature whether the opaque material is definitely missing in females.

The most reliable method of sexing monitor lizards is by endoscopic examination (Schildger et al 1993, Schildger & Wicker 1992). This can only be done by a vet and involves anaesthetising the animal, making a small hole in its body wall, inflating the body cavity with gas and viewing the ovaries or testes through an endoscope. In the hands of an expert this procedure looks very simple. The examination may also reveal internal disorders that would otherwise go undetected until manifesting themselves as sickness. Again this method may be ineffective when applied to young animals, but when used on adults it is virtually infallible.

Because male monitor lizards are more active than females they tend to be caught more easily, and as a result females are often more difficult to obtain. Because at present there is no easy way of sexing most monitors with 100% accuracy, the best policy to ensure the presence of a pair is to obtain about half a dozen young monitors, allow them to grow up with alternating periods of solitary and group confinement (if they will tolerate each other) and try to deduce their sex by their behaviour towards one another. Unfortunately there are few obvious sex-specific behaviours in monitor lizards. Males often attempt to mate with each other and animals of both sexes will engage in ritual combat.

There are many other good reasons why juvenile animals are to be preferred. They adjust better to life in captivity, are less likely to be loaded with dangerous parasites and if cared for properly will live for at least a decade. Usually it is not possible to determine where a captive animal originated. This is unfortunate because some species have enormous ranges and specimens from very different habitats may prove incompatible. This is especially true of Bengal, Nile, mangrove, desert, water and white-throated monitors. Reports seem to indicate that breeding has occurred between some "subspecies" of monitor lizard, but it is not known whether fertile offspring were produced.

How long do Monitors live?

There are very few records of the longevity of monitor lizards in captivity (Flower 1925, 1937, Snider & Bowler 1992, Bennett 1994) and virtually none of their lifespan in the wild. The record appears to be held by the Taronga Zoo in Sydney, where a Komodo dragon was kept for 24.5 years. The animal was adult when acquired, and a total lifespan of about 50 years has been predicted for this species (Auffenberg 1981). The Tel Aviv University Zoo maintained an adult desert monitor for 17 years, and estimated its age at death as at least 25 years. Other large monitors lizards are recorded as surviving for 20 years or more in captivity. Unfortunately there is much less information available on the lifespan of the dwarf monitor lizards. A female spotted tree goanna kept at the Basel Zoo in Switzerland was still laying eggs after 20 years in captivity (Bennett 1994b). Of course, the reported figures tend to be exceptions rather than the norm but they do indicate that a life expectancy of at least a decade is not unreasonable and that many specimens of both large and small species can live for at east twice as long. Monitor lizards therefore, although they do not attain the great ages recorded for crocodilians and chelonians, are amongst the most long lived of the squamates. Considering that most species can attain sexual maturity within three years it can be seen that the reproductive potential of these animals is enormous and that females of the more prolific species may be able to produce more than 500 eggs in a lifetime.