Argentine black and white tegu

The specific name, merianae, is in honor of German-born naturalist Maria Sibylla Merian.[5]

A black and white tegu seen in Florianópolis, Santa Catarina, Brazil.

As a hatchling, Salvator merianae has an emerald green color from the tip of its snout to midway down its neck, with black markings. The emerald green becomes black several months after shedding. As a young tegu, the tail is banded yellow and black; as it ages, the solid yellow bands nearest to the body change to areas of weak speckling. Fewer solid bands indicates an older animal. A tegu can drop a section of its tail as a distraction if attacked. The tail is also used as a weapon to swipe at an aggressor; even a half-hearted swipe can leave a bruise.

Tegus are capable of running at high speeds and can run bipedally for short distances. They often use this method in territorial defense, with the mouth open and front legs held wide to look more threatening.

Adult males are much larger than the females and can reach 3 ft (92 cm) in length at maturity. They may continue to grow to lengths of 4.0–4.5 ft (120–140 cm).

The females are much smaller, but may grow up to 3 ft in length, from nose to tail. They have beaded skin and stripes running down their bodies. Adult females can reach a weight of 2.5–7.0 kg (5.5–15.4 lb).[6]

The skull is heavily built with a large facial process of the maxilla, a single premaxilla, paired nasals, a single frontal bone, and a single parietal bone. Biomechanical analyses suggest the posterior processes of the parietal might be important for dealing with torsional loads due to posterior biting on one side.[7] In the large adult animals, the posterior teeth are larger and more rounded than the anterior teeth.[8]

Blue tegu

An immature blue tegu resting

The blue tegu is a variant known for its light blue coloration, which is most intense and vivid in the adult males. Even immature animals can be easily distinguished from other mostly black and white tegu species by the "singe mark" on their nose. They are among the more suitable tegus for pets, and can be easily tamed but in the wild will either try to run away or react aggressively if provoked. There is much controversy about the correct scientific classification of this animal. Large-scale taxon sampling of the teiids has not led to any strong resolutions based on morphological and genetic data;[10] the majority of data about the blue tegu comes from hobbyists. Some believe it is a mutation of the Argentine black and white tegu, while others, including the original importer,[11] believe it is sufficiently different to have its own classification. The first blue tegu to be exported from South America was in a wholesale shipment of tegus from Colombia.[11]

The coloring of a blue tegu can range from a simple black and white animal to albino to a powder blue to even "platinum" which is basically a high white morph of the species. The colouration doesn't tend to appear until the animal reaches sexual maturity around the age of 18 months or 2 feet or more in size. Just like the Argentine black and white tegu, the blue tegu has a very quick growth rate, almost reaching 75% of its full length in a year. Their adult length can vary from 2.5 feet in females to sometimes even longer than 4 feet in adult males. Unlike other lizards these are very heavily built animals ranging from 7 to 12 pounds or more when fully grown. Size is relative to genetics as well as husbandry and diet.

Salvator merianae has recently been shown to be one of the few partially warm-blooded lizards, having a temperature up to 10 °C (18 °F) higher than the ambient temperature at night time.[13] However, unlike true endotherms such as mammals and birds, these lizards only display temperature control during their reproductive season (September to December), so are said to possess seasonal reproductive endothermy. Because convergent evolution is one of the strongest lines of evidence for the adaptive significance of a trait, the discovery of reproductive endothermy in this lizard not only complements the long known reproductive endothermy observed in some species of pythons,[14] but also supports the hypothesis that the initial selective benefit for endothermy in birds and mammals was reproductive.[15][16]

Tegus are omnivorous. Juvenile tegus in the wild have been observed to eat a wide range of invertebrates, including insects, spiders, and snails.[17] They also eat fruits and seeds. As they grow they become more predatory and the protein content of their diet rises. They may seek out eggs from other reptiles and from birds' nests, and will eat small birds and other vertebrates. In adulthood tegus continue to eat insects and wild fruits, and it is assumed that such components include desirable or essential nutrients.

In captivity, tegus commonly are fed high protein diets that include raw or cooked flesh such as ground turkey, canned & dry dog food, commercial crocodile diet, chicken, eggs, insects, and small rodents. The inclusion of fruit in the diet is recommended. Though some captive tegus do not readily eat fruit, others enjoy banana, grapes, mango, and papaya.[18] However, there is evidence that, as in most husbandry of carnivores, it is good practice to cook most of the egg in the diet, so as to denature the protein avidin, that occurs in the albumen. Raw avidin immobilises biotin, so excessive feeding of raw eggs may cause fatal biotin deficiency.[19]

As adults, they have blunted teeth and exaggerated lateral pterygoidal muscles which allow them to be generalist feeders. In captivity, they have been observed eating various feeder insects like mealworms, superworms, earthworms, silkworms, crickets and roaches, as well as vertebrate prey like mice, rats, fish, turkey (offered in a ground form), rabbit, quail, and chicks. Crustaceans such as crayfish are also readily consumed. Like all lizards, blue tegus need a properly balanced diet; incomplete prey items such as insects or ground meat require dusting with a mineral/multi-vitamin supplement. Vitamin deficiencies can lead to trouble shedding skin, lethargy and weight loss; a calcium deficiency can lead to metabolic bone disease, which can be fatal.[20]

Predators of tegus are pumas, otters, jaguars, snakes, and birds of prey.

Tegus make amenable pets, as they tend to become acclimated to their owners and are generally quite docile as adults. They are intelligent and can even be house-broken. A healthy tegu can live for 15 to 20 years in the wild, and possibly even longer in captivity. However, as with most reptiles, if they are not handled regularly, they show more aggressive behaviour; their bite can be painful and damaging due to strong jaws (1000 N bite force, stronger than a dwarf caiman, partly due to the short, deep skull) and sharp incisor teeth in the upper jaw. Tegus do not produce venom. Tegus will perform a threat display if they are upset or stressed. The first stage is huffing, or very heavy breathing, which means "be careful". Further interference causes the animal to start lashing its tail, somewhat like a moving snake. In wild animals, a third stage of stamping the front feet or "dancing" is seen. If these hints are ignored, then the tegu can charge and may bite, which will require hospital or veterinary attention.

As the name would suggest, this tegu is native to Argentina, but also Brazil, Paraguay, and Uruguay.[21]

Blue tegus, like other tegus, may breed up to twice a year. They only lay between 18 and 25 eggs in a 'clutch', sometimes more dependent upon animal size and husbandry as well as individual health of the gravid female.

The two prominent loreal scales between the eye and nostril of this black and white tegu, plus its round pupil, identify it as belonging to the genus Salvator.

In 1839, this species of tegu was originally described as Salvator merianae. However, beginning in 1845 and continuing for 154 years, it was confused with Tupinambis teguixin, and was considered a synonym of that species. In 1995, it was again given species status as Tupinambis merianae because subsequent studies had shown that the gold tegu, Tupinambis teguixin, is distinct from it. In 2012, the black and white tegu was reassigned to the resurrected genus Salvator as Salvator merianae.[29]

S. merianae is called the "Argentine black and white tegu" to distinguish it from the "Colombian black and white tegu", which is another name for the gold tegu. Unscrupulous or incompetent pet dealers sometimes pass off gold tegus as black and white tegus.

S. merianae and T. teguixin can be distinguished by skin texture and scale count:

• S. merianae has two loreal scales between eye and nostril.
• T. teguixin has only a single loreal scale between eye and nostril.
• S. merianae has round pupils, whereas Tupinambis species have reniform pupils.

In the ecotone between the arid Chaco and the Espinal of central Argentina they are known to naturally hybridise with the Red tegu (Salvator rufescens) with a stable hybrid zone.[30]

• Gold tegu
• Tegu
• Teius
• Teius teyou

• Avila-Pires TCS (1995). "Lizards of Brazilian Amazonia (Reptilia: Squamata)". Zoologische Verhandelingen. 299 (1): 553–557. ISSN 0024-1652.
• Harvey, Michael B.; Ugueto, Gabriel N.; Gutberlet, Ronald L., Jr. (2012). Review of Teiid Morphology with a Revised Taxonomy and Phylogeny of the Teiidae (Lepidosauria: Squamata) (PDF). Zootaxa. 3459. Auckland, New Zealand: Magnolia Press. ISBN 978-1-86977-988-7.
• Care for Black and White Tegus

• Renner, Rebecca (2020-11-18). "This dog-size lizard is spreading through the southeastern U.S." National Geographic. Retrieved 2020-11-19.