Probably the four most important things when caring for a monitor are caging, substrate, temperature, and food. If you can provide these, you'll probably do fine keeping a monitor.
As far as caging goes, you've got to realize that not only are monitors large animals, they are also quite active. They need enclosures large enough to accomadate their active natures. In my opinion, the minimum sized cage for a small female argus monitor would be about 1 meter by 2 meters. A whole room would be better.
Caging for an adult male argus monitor.
These cages are made with a base consisting of an entire 8' x 4' sheet of plywood resting on a large galvanized steel stock tank. The stock tank holds dirt to burrow in. This enclosure could also hold a mating pair of arguses or other mid-sized monitors.
Another view of the same cage.
A different cage, this time taller.
The cage should have a place to hide. The hiding spot should be small enough that it feels tight to the monitor. The monitor should be able to feel the hide box pressing up against its back and belly. This helps them to feel secure. A cardboard box with a hole cut in it does not really work, it is usually to spaceous. A piece of plywood with 2x4s screwed into the bottom to support it a small distance above the ground is readily accepted by larger monitors. For smaller monitors, replace the 2x4s with thinner pieces of wood, or just lay a sheel of wood on top of a loose substrate so the monitor can make its own burrows under the wood. Cork rounds also work well if they are about the diameter of the monitor, they seem to emulate the hollow logs that can be found in the wild.
A plywood hide spot.
A cork round hide spot.
A hide spot is important for more than just security. Wild monitors use burrows to cool off when it is too hot, to keep from getting too cold when the outside temperature drops too low, and to help conserve moisture. Monitors know that a burrow needs to have the proper combination of temperatures and humidities, but us people just do not seem to appreciate what really makes a good burrow. What seems like a fine burrow to us may be uncomfortable or even unacceptable to a monitor. Thus, it is a good idea to provide several hide spots, so the monitor can choose one that has the right environment. One idea is to take the plywood and spacer design described above, make a whole bunch of them, and stack them on top of each other underneath the heat lamp. The top hide spot, right under the heat, will be nice and toasty. Lower hide spots are progressively cooler. It also lets the monitor get closer to the heat lamps, which can be a good thing.
A plywood stack. This is narrower than the ideal stack, but Dash and Varanica seem to use the various levels to good effect.
This takes us to substrate. The best substrate for an argus monitor is dirt. Just plain dirt. Why? Argus monitors really like to dig. That's what they are good at, and they love to practice their trade. In particular, covering the entire cage with dirt lets the argus monitor digs its own burrow just where the conditions are best. A burrow in dirt is the best possible hiding spot for an argus, because not only does it provide security, but it allows the monitor to use the burrow for water conservation and thermoregulating like a monitor would naturally do in the wild.
The trick is, it has to be deep enough to make a good burrow in, 30 to 60 cm of dirt seems to work just fine. In addition, there are good dirts and bad dirts. Argus monitors prefer a sandy dirt, other monitor species like different kinds of dirt and some of them can be awfully particular about it. Some people are lucky enough that they can just go out in their back yards and dig up dirt for their monitors. When I tried this, the dirt quickly turned into a fine dust everywhere that it didn't get wet, and became a reeking sticky oozy paste everywhere it did get wet. If you can't get dirt from your backyard, you have two options: dig it up somewhere else and haul it back, or buy it. If you are going to haul it, you'll need at least a pickup truck bed's full of dirt for a typical argus enclosure. If you are going to buy it, you can mix together about 12 50 lb bags of playsand with 12 40 lb bags of topsoil for something that works reasonably well for an 8' x 4' enclosure, if you buy the right topsoil. Unfortunately, topsoil probably varies quite a bit from vendor to vendor and from region to region even with the same vendor. An alternative it so buy a truckload of dirt from a landscaping company.
The big problem with dirt is that it is heavy, you need a lot of it, and so you have to do a lot of hard labor to get it into your monitor enclosures. Other substrates can be used, but the difference a good dirt makes is so significant that I would not recommend anything else over the long term. For animals undergoing medical care or quarenteen, or for those in need of temporary housing, newspaper, care fresh, or cypress mulch or aspen chips can be used.
Dirt for burrowing.
I find that argus monitors in particular often like to dig at their food. For example, even when you present beetle larvae on hard ground, arguses will often dig and scratch around to try to "dig up" their food. I believe this has a similar origin to the food "washing" of racoons, or to food peeling by agoutis. In these cases, the animal has an instinct to prepare or acquire its food by a set of ritualized actions (foraging in the water under rocks with its hands in the case of racoons, peeling hard shelled nuts for agoutis, or digging up subterranian prey in the case of argus monitors). When these animals are prevented from employing their instinctive methods of food acquisition, they will employ them when not appropriate to the situation out of something akin to frustration.
Another behavior which is an artifact of captivity is constant digging or scratching at the sides of the enclosure. Sometimes this digging or clawing is just an adjustment phase the lizard will go through before it settles in, but if it is still digging and clawing at the sides after a week or so, consider it a warning that its housing conditions are inadequate. there is something in its enclosure which is missing that the monitor instinctively knows it needs. Does it have enough space? Is there a large enough range of temperatures for the monitor to warm up to its preferred body temperature and to cool off when it needs to? It is too dry? Too humid? Is there a suitable hide spot? I notice that my arguses, which are kept in large enclosures with a complex environment, do not usually dig unless they smell food, and although sometimes they will try and get out the window, this behavior is fairly infrequent (at least once they adjust to their new home). Be aware that gravid females will often dig, dig, dig. They are trying to make a nest for their eggs, and will dig in every available corner to try to make one. If you have your monitors on deep dirt that holds a burrow, she will naturally make a nest and lay her eggs in it. Otherwise, the best thing is to provide a nest box for the female.
In addition to a hide spot and substrate, your monitor will need a water dish. They really appreciate the chance to soak, so make it big enough to submerge the monitors entire body. A cat litter pan suffices for most monitors, but big ones may need a concrete mixing pan or even a bathtub. Monitors often like to relieve themselves in their water dish. This means that you will need to change the water frequently, but also means that you do less work keeping the rest of the cage clean. Argus monitors are so active that they tend to track water all around their cage, making it into a soggy mess. What I find helps is to put the water dish inside a somewhat larger dish to catch a lot of the water that would otherwise be tracked onto the substrate and floor. It doesn't solve everything, but it helps. If you find your argus monitor spending a lot of time in the water, chances are the cage is too dry. Once again, if it could dig a burrow in dirt, it would be able to regulate its humidity at the same time, and the problem would be solved. The next best thing would probably be to give your monitor a tight hide spot packed with peat moss or dirt or coconut pith planting mix or something that will hold moisture.
A concrete mixing trough used as a water dish.
Some monitors appreciate branches to climb on. Some could care less. If you give them climbing branches, make sure they are very sturdy. Live plants are pretty much right out. Argus monitors will climb the plants and break off the branches, and will enthusiastically dig up the potting soil and spead it all over their cage. If you really want to use live plants, expect to replace them frequently.
As for temperature, keep in mind that the active temperature range of any monitor is between 30 and 40 degrees Celcius, with a prefered temperature of around 35 to 36 Celcius. Since monitors are cold blooded, they need outside sources of heat to warm up, but they also need cooler places to shed excess heat when necessary. I like to keep the ambient air temperature around 25 to 30 C except for a possible winter cooling period, when the ambient temperature can drop to around 20 C. (Note that a winter cooling period is not necessary, even for breeding purposes. Argus monitors can be kept at high temperatures year round, and they will stay active, healthy, and the females will cycle regularly.) The basking spot is kept significantly above 40 C. I like to keep a central area under the basking spot at least as large as a monitor's body as hot as possible so long as it is not hot enough to burn. This allows the monitor to warm up quickly when they need to. When basking, they will almost always choose this hottest spot. A good rule of thumb is that if you put your hand on the hottest part of the basking spot and it is not hot enough to cause pain, it is not too hot. A range of 45 to 55 C is probably fine. Remember, though, that your lizard also has to be able to cool off. It the lizard's internal temperature goes above 42 C, its brain will addle and it will die. The same thing happens to people, too, except that people make more use of cooling by evaporation, monitors only use evaporation to cool themselves when they are in thermal stress and about ready to overheat. They far prefer to rest in the shade where it is cool. At night, the basking lamps can be turned off and the lizard cooled. They will warm up again in the morning.
Racks of 4 90 Watt halogen floodlamps are used to create these basking spots.
Basking heat is best supplied by radiant heat. I use racks of 90 Watt halogen flood lamps in a line large enough to provide a more or less even swath of high temperature as long as the monitor's body. Incandescent bulbs provide less radiant heat for their wattage than halogens, both are equally good at raising the ambient heat, but halogens are better for basking spots.
Some people wonder about UV light. This does not seem to be neccessary for most monitors. Even rapidly growing juveniles and reproductive females do fine without UV as long as they are fed a good diet. I do often use the UV producing mercury vapor bulbs, but this is because these bulbs also more closely mimic the visible spectrum put out by the sun, so they really help to bring out the monitor's colors. A single 100 Watt mercury vapor fixture or self balasted bulb in combination with the halogen basking lamps provides a pleasing light for viewing your lizard. A mercury vapor fixture is cheaper in the long run than a self balasted mercury vapor bulb, especially since the self balasted bulbs often burn out after a month or two in spite of their advertizing that they last a whole year at least. The newer bulbs might do better, but when I bought eight self balasted bulbs in 2000, most had burnt out within three months and none lasted six months.
Arguses, like most monitors, can and should be fed a wide variety of food items. Crickets, mealworms, superworms, giant tropical cockroaches, earthworms, mice, rats, chicks, and hard boiled eggs are all eagerly devoured when available. It is a good idea to feed whole vertabrates regularly, because whole vertabrates have all the necessary vitamins, minerals, and other foodstuffs needed to stay healthy. On the other hand, if feeding them rodents, it is a good idea to kill the rodents first. Although an argus monitor can kill a mouse nearly every time without getting hurt, sometimes the mouse gets lucky. Rodents have long, chisel-like incisors that make deep, easily infected punctures. Not only that, but frozen mice are usually cheaper, and are always less stinky, easier to catch, don't need to be fed, won't bite you, and in general a lot less trouble. If your pet store carries frozen rodents, its worth your while to get these over live ones.
Giant tropical roaches.
One thing that I have noted with argus monitors is that it is difficult to feed them too much. Unlike savannas, they do not seem to get obese. All excess food goes into growth (for juveniles), making eggs (for females), or just their generally high activity levels (for all animals). In particular, females will regularly develop and lay eggs. If well fed and kept unde rthe appropriate conditions, a female argus can lay every six to eight weeks, year round. They do this whther or not a male is around, but obviously, without a male the eggs will not be fertile. A gravid female begins to look fat or, more accurately, bloated. A week or so before laying eggs, she will go off feed and begin digging around everywhere. If you are not using a deep dirt substrate, this is a signal that you need a nest box. I have made mine out of 10 gallon rubbermaid containers, with the lid firmly affixed but a hole drilled out of the side large enough to allow a gravid female to get in and out (use one of those attachments for drilling out the hole in doors where doorknobs go). This container is then filled with damp coconut pith bedding. The female will begin digging in this dark, damp hole and probably lay her eggs in there several days later. Using a nest box can be fairly stressful on the female if conditions are not right, however, which is another reason to use dirt - it is a lot easier on the female at egglaying time. She will be very skinny when she finishes laying and will probably be ravenous. Of course, they are always ravenous, so you might not notice much difference from her normal behavior, but it would be a good idea to feed her heavily for a while to get her body weight back up. That means, of course, that she will soon start to develop eggs again. By the way, argus monitors are easy to breed. Just introduce a male and female and they produce fertile eggs regularly. My pairs of arguses breed regularly and produce frequent clutches of eggs.
View of a nest box.
To incubate the eggs, place them in a damp medium such as vermiculite or pearlite. Damp does not mean wet. I've lost many clutches to an overly moist nesting medium before I figured out what I was doing wrong. The nesting medium should be just barely perceptably damp to a probing finger. Bone dry is as undesirable as obviously damp or soggy. Check the eggs frequently to keep the moisture level right.
A few notes of caution. All my females hate each other. They try to rip each other to shreds every chance they get. This behavior may be alleviated by raising the females together from the time they are very young. Males and females will often get along just fine, depending on their individual personalities. Adult males occasionaly get along, but more often it turns into a big dominance contest or just a bloodbath as they tear into each other with teeth and claws. Also, it is a good idea not to feed argus monitors together. They are such agressive feeders that they will often injure each other in a sort of shark-like feeding frenzy.
Chris snags a mouse
Monitors are very quick learners. Chris very quickly found out
that the hemostats mean food, and even which end holds the food. She is
still not all that clear on when the heomstats have food in them, though.
For obvious reasons, I do not feed my arguses by hand. I offer them food with a long (about 1 meter) pair of hemostats, or I give them beetle grubs or giant cockroaches in a large conatiner. I've been bitten a few times by adult arguses and I've found that their bites are much more serious than those of much larger Niles and savannas. Although their jaws do not have the crushing power of the African monitors, their teeth are designed for slicing flesh; sharp, teardrop shaped in cross section, and slightly recurved toward the back to make an efficient cutting blade. The African monitors typically have sharp conical teeth for piercing and holding or blunt crushing teeth for cracking shells. The sharp cutting teeth of the arguses combined with the very well muscled necks and torsos of the monitor lizard family give a very nasty wound when they can bite and thrash. One one occasion, an argus monitor drove one of its teeth through the first joint on my left index finger. This caused the joint to swell painfully for several weeks and prevented full range of motion in this finger for many months. On another occasion, my right index finger was sliced open. The wound was deep, covered half the width of my finger, and bled freely. My finger swelled up for several days and the wound did not close for about a week. Noteably, in both of these cases, the bite was a quick grab and release. In neither case did the monitor try to hold on and "go for the kill" by thrashing about. I've seen mice ripped nearly in half by juvenile argus monitors using this technique, I'd hate to see what an adult could do to a person. I'm not trying to scare you away here, but you need to realize what these animals are capable of. Not only that, but they are fundamentally wild animals, even if they have lost their fear of humans, and incredibly athletic wild animals at that. Your pet argus will probably have faster reactions than you do. It is important to take care when the argus is likely to be nervous or if it is in feeding frenzy mode. Most of the time, a nervous argus is just hiss and bluff, but if you suddenly lunge or grab it, it may bite. They may also bite if your fingers smell like their normal food. I have a pair of heavy leather welders gloves, padded and reinforced with kevlar, for situations where I feel that my pets may try to take a chomp out of me. These can stop the bite of a small monitor and blunt and absorb the bite of a large argus enough th prevent serious wounds, although on a couple memorable occasions, one of my big male arguses was able to give me a scratches and shallow cuts with his teeth through the heavy leather gloves while in the process of shredding the gloves.
A female argus is likely to get about the size of a large male ferret, say, around 3 kilos. My male arguses are both larger than a large tomcat, 10 kilos each the last time I weighed them. I have heard that one of the subspecies of the Australian argus monitor gets even larger, large enough to rival the lacies and perenties in size. I'd love to get one of those! Nevertheless, the New Guinea arguses on the American market today are certainly very spectacular creatures.
A photo showing the size of Dash, an adult male
argus monitor, compared to a human (me). To put things in perspective, I'm
193 cm high, about 90 kilograms.
Photo courtesy of Mark Silver
A photo showing the size of Chris, a medium sized female argus monitor, compared to a human. No, the bandaged thumb is not from a monitor bite. This photo was taken while displaying Chris at the Pacific Northwest Herpetological Society's annual show at the Pacific Science Center at the Seattle Center in Seattle, Washington.