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Tegus are members of the Teiid family of lizards, and are closely related to the North American Whiptails (Cnemidophorus species) and the Latin American Jungle Runners (Amieva species). In appearance and habits, the Tegus mimic the African and Asian Monitor Lizards, thought they are not closely related. This is an example of what biologists refer to as "convergent evolution," in which organisms from different groups evolve towards the same body plan and habits in response to similar environmental niches.
Taxonomically, the Tegus are the subject of much debate. There are at least three recognized species of Tegu. The most highly prized is the Red Tegu, Tupinambis rufescens, which is found in the northern part of Argentina. The Black and White Tegu, Tupinambis teguixin, is native to Argentina, Brazil and Uruguay. It is not often seen in captivity. The most common Tegu found on dealer lists is the Black Tegu, Tupinambis nigropunctatus. The Black Tegu is found throughout the Amazon Basin.
Another variant of T. nigropunctatus is the Gold Tegu, once considered to be a separate species but now classified as a geographical race of the common Black Tegu. It has a black and yellow pattern, with the most sought-after individuals being almost pure yellow or tan.
Tegus (the name comes from a Latin-American Indian word for "lizard") are large and powerful animals with a reputation for aggressiveness. The Red Tegu is the largest, but ironically is also reputed to be the most docile. The Gold Tegu is generally held to be the most aggressive--but this seems to be more a matter of individual temperament than overall species behavior.
A full-grown male Tegu will typically reach a length of 3 to 3½ feet, and weigh around 8 pounds. (The largest Tegu known was just shy of 5 feet long, and weighed over 15 pounds.) Although some individual lizards will adapt to the human presence and be more or less amenable to handling, most will be difficult to handle, and are capable of delivering punishing tail slaps and deep scratches, as well as nasty bites. Even a "tame" Tegu can turn on its keeper in an instant if it is startled or spooked. None of the Tegu species is suitable for the beginning herper.
A large number of Tegus are imported into the United States each year from Latin America. Nearly all of them, however, arrive only as skins, which are widely used in the leather trade to produce "alligator" wallets, shoes, and belts. A single adult Tegu skin can bring an Argentine farmer almost as much money as he can make in a month's wages. In their native Latin America, Tegu tails and legs are also highly prized as food.
Tegus require spacious, sturdily-built cages. Juveniles will require at least 20-gallon tanks. Adults will need specially-built cages--the minimum size for an adult lizard is 4' x 4' x 3', and bigger is better. These active lizards will utilize every square foot of space that you can give them. Since Tegus have powerful legs and claws, any accommodations will have to be tough, and able to withstand a lot of abuse. A securely locking lid is an absolute must--Tegus are very good climbers, as well as astonishing leapers. An adult lizard can easily get over a three or four foot barrier.
Although female Tegus may sometimes share a cage together without complaint, males will be aggressive towards each other. Even if they "get along," these active lizards may still accidentally injure each other with their sharp claws. It is recommended that these lizards be housed individually.
A large water dish or pool is necessary. Tegus are excellent swimmers, and sometimes like to soak and bathe. In the wild, they are seldom found far from a water source, and their preferred habitat consists of heavy jungle along rivers or streams. Since Tegus seem to prefer to defecate in water, the water pan in their cage will have to be changed often.
The substrate for a Tegu tank must be chosen with practicality uppermost in mind. It will have to be changed often. Some substrates, such as pine shavings, crushed corn cob, or aquarium gravel, should be avoided. If the Tegu accidentally swallows any of these substrates, it can produce an intestinal impaction or blockage that can have fatal consequences. Some keepers use reptile bark or aspen chips in their cages. Shredded coconut bark is another excellent choice, because it can be used dry or moist--and will not turn moldy when wet. Ordinary utility carpet mats can also be used; these have the advantages of being inexpensive and easy to clean. Simply brush off uneaten food or feces, and run them through your washing machine when they become heavily soiled.
Tegus are tropical animals, and require warm humid conditions. Daytime temperatures should be in the high 70's to low 80's, dropping to the mid-70's at night. Since Tegus are, like all reptiles, exothermic, temperature control is one of the most vital factors in keeping them in captivity. Nearly every potential health problem that these lizards face can be directly traced to how well their temperature requirements are being met, and probably more captive Tegus are killed by being kept at a too-low temperature than any other cause.
The cage must also be well-ventilated. Screened areas at the cage top and bottom will provide a proper air flow, but these should be located where the lizard cannot reach them, or it may rub its nose raw on the wire. In home-built wooden cages, a series of ventilation holes can be drilled along the top and bottom edges.
The best setups will provide a range of different temperatures, or a "temperature gradient," within the cage, allowing the Tegu to select the temperature that it wants by moving from warmer to cooler areas as needed.
The electric "hot rocks" or "sizzle stones" which are often sold in pet stores should never be used. The cheaper ones usually do not have any means of controlling the heat output, and thus there is no way to regulate the temperature. They are also prone to malfunctions. Since lizards have few nerve endings in their bellies, they will often sit unknowingly on an overheated hot rock, completely unaware that their skin is being severely burned. This can lead to severe injuries and death.
Another problem is that sizzle stones do not warm the surrounding air very much, and only heat one small spot in the tank. They do not provide a usable temperature gradient, and do not allow the lizard to effectively thermo-regulate.
The best way to set up a Tegu's basking spot, and provide it with necessary UVA/UVB at the same time, is to buy a multi-purpose incandescent heat bulb such as ZooMed's PowerSun, and mount it outside of the cage, at one corner of the screen lid. Like all diurnal (active during the daytime) lizards, Tegus need access to unfiltered ultraviolet light. Reptiles use the ultraviolet wavelengths in sunlight to manufacture Vitamin D3 in their skin. This vitamin is essential for proper bone development. Lack of UV light causes serious skeletal illness which is usually fatal. (Please note that both glass and plastic block the useful UV rays, so your UVA/UVB bulb should be used with screening rather than glass or plastic.) It is also helpful to provide your Tegu with as much unfiltered natural sunlight as possible, by taking it outside for periods of time on warm days.
A flat pile of rocks should be arranged directly below the basking spot. The basking light thus produces a localized "hot spot" for basking, while leaving the far end of the tank relatively unheated. The Tegu can then warm up when it needs to by following its natural behavior pattern--it looks for a warm sun-baked rock to rest on.
A very useful arrangement is to connect the basking light to an electrical timer, to turn it on and off automatically. A light schedule of twelve hours on, twelve hours off, which mimics the length of the tropical day, is best.
Tegus are large active predators, and will eat virtually any animal they can overpower. They track their prey with their long forked tongue, which transfers scent molecules to the Jacobson's Organ in the roof of their mouth in a manner similar to snakes.
Juvenile Tegus will do well on a diet of crickets, provided these are "gut-loaded" and/or dusted with vitamin and calcium powder. Even young lizards have large appetites, and can easily put away 75 or so crickets a week. They will also accept pre-killed pinkie mice.
Adult Tegus can be fed a staple diet of whole pre-killed or frozen-and-thawed rodents. These can often be simply dropped into the cage, or offered in a food dish. If your Tegu prefers its prey to be moving, it can be jiggled on the end of a pair of long tongs or forceps (NEVER feed a large Tegu by hand, unless you want your nickname to become Three Fingered Louie).
Most Tegus will also accept eggs, which make up a large part of their diet in the wild. There is some reason to believe that unfertilized eggs may be harmful to large predatory lizards over the long term. To play it safe, it is best to offer eggs only as an occasional treat.
Most authorities consider Tegus to be omnivorous; they will, on occasion, accept a piece of fresh sweet fruit, such as banana or melon, that is placed in their food dish.
Handling a large Tegu can be an adventure, to say the least. Wild-caught adults are irascible and mean, and usually never lose their fear of humans. Captive-bred animals and younger wild-caught can be tamed somewhat, depending on individual temperament. However, great care should be taken around even "tame" Tegus, as they are very fast, very excitable, and can inflict a respectable amount of damage on the unwary herper.
Young animals should be handled often, to accustom them to the process while they are still too small to effectively object and inflict any serious damage. If gently handled for fifteen or twenty minutes every day, a young Tegu will come to learn that humans are not a threat, and will learn to tolerate handling.
As soon as you approach a captive Tegu, you are likely to hear a series of short "huffs." The frequency of the tongue-flicking will also increase as the Tegu tries to assess the situation. This is a sign that the lizard is nervous or excited, and although it doesn't necessarily mean the Tegu will try to bite, it does mean that it's not happy with the situation and needs to be watched carefully.
If further excited, the lizard will often raise itself up on its legs and swell out its chest in an attempt to look intimidating. As a final warning, it may face the intruder and gape its jaws widely to display the sharp conical teeth. A tail-lashing usually follows, and, if all else fails, a bite.
When handling a large Tegu, the first priority is to control the tail. Gently grasp the base of the tail, near the vent, with one hand, at the same time gripping one of the rear legs between the fore and middle fingers. Lift up a bit so the rear feet are off the ground (this prevents the lizard from turning quickly) and slide your other hand, palm up, along the belly until you reach the front legs. Pin one of the front legs between the fore and middle fingers (your forefinger should encircle the neck just behind the jaws and the lizard's chest should lie in the palm of your hand). Lift the lizard and pin its tail between your arm and upper body. Use the fingers of one hand to control the neck and front legs, and use the other hand to press the back legs down along the tail. This will allow you to carry the lizard without risk from the tail, claws, or teeth.
To make handling easier, the Tegu's nails should be periodically trimmed. This can be done using the commercial nail clippers sold for dogs or iguanas--the ones that look like a short pair of scissors with a half-moon shaped cutting area. Nail-trimming a large Tegu is a two-person operation. One person holds the lizard and controls it, the other does the actual clipping. Only the very tip of the nail should be trimmed; if you cut too close to the base of the claw, it will bleed, and your Tegu will be VERY annoyed. A Tegu's claws should be trimmed every month or so.
Tegus are not often bred in captivity. In the wild, breeding takes place in the fall. As is typical with most lizards, mating is a rather rough affair, with the male grasping the back of the female's neck in his jaws before twining his tail with hers. Gravid Tegu females use their powerful claws to dig a shelter (sometimes they rip open insect nests) and lay 4-6 eggs there. The newly emerged hatchlings are about five inches long, and have a protective coloring pattern of greenish gray with darker spots. They assume their adult colors after about four weeks.
The Tegu is not as commonly found in captivity as are the more popular Monitors. This is unfortunate, since it is an attractive, intelligent, and fascinating animal with a definite "personality." When kept by an experienced herper who is prepared to meet the requirements and responsibilities of owning a large potentially-aggressive lizard, the Tegu can be a worthwhile addition to any collection.