Monitors, Goannas, and Earless Monitor: Varanidae

views updated




The monitors, goannas, and earless monitor all have a similar overall appearance, although some are rather small and others are very large. The smallest species is the Australian pygmy monitor that only reaches about 6.7 to 7.9 inches (17 to 20 centimeters) in length from snout to tail tip and weighs just 0.28 to 0.71 ounces (8 to 20 grams). The family contains the largest lizards in the world. The heaviest is the Indonesian Komodo dragon. This immense animal can grow to be at least 9.9 feet (3 meters) long and 330 pounds (150 kilograms). Many people consider the crocodile monitor to be the world's longest lizard. They may grow to 12 feet (nearly 3.7 meters) long from snout to tail tip, or as some reports claim, the lizards can reach a whopping 15 to 19 feet (4.6 to 5.8 meters) in length.

The monitors, goannas, and earless monitor have heavy bodies and long necks. Their tongues are long and forked, and they have noticeable, sometimes large, eyes. Many have somewhat saggy skin that hangs in small folds on their sides and necks. Most of the members of this family have teeth with edges like saw blades, which help them tear through the skin and flesh of their prey.


Australia is home to about one-half of the known species. Members of this family also live in Africa; central to southern mainland Asia; Southeast Asia, especially the Malaysian and Indonesian islands; and Papua, New Guinea.


These lizards live in many different habitats from dry deserts and grasslands, to lush forests and swamps. Some rarely if ever leave the land, and others rarely leave the water. Several species climb trees. This includes the green tree monitor of New Guinea and Australia, which has a very strong tail that it uses when climbing.


Most members of this family are meat-eaters. The smaller species typically dine on insects, centipedes, worms, and other invertebrates (pronounced in-VER-teh-brehts), which are animals without backbones. Medium-sized species eat lizards, lizard and turtle eggs, and young mammals and birds, while the very large monitors will capture, kill, and eat deer, monkeys, adult birds, wild pigs, buffalo, and other big animals. Monitors also eat carrion (KARE-ree-un), which is the flesh of an already-dead animal. They are not picky eaters, and many will even eat young of their own species. A few species eat fruit.

Members of this family spend a good part of the day looking for food, with some traveling 0.6 mile (1 kilometer) or more between sunup and sunset. They flick their tongues to pick up the scent of a prey animal and then rely on their eyesight and their ears to help hunt down the animal when they get close. Some species, including the sand monitor, swing their heads back and forth while flicking their tongues so they can pick up scents from a wider area and then track animals, especially small lizards, to their underground burrows. They use their long claws to dig up the lizards. Other species, such as the Komodo dragon, sometimes hunt by ambush, which means that they sit very still so they are not obvious and wait for a prey animal to wander by. The Komodo dragon then rushes from its hiding spot and grabs the animal.


These lizards are active during the day. Those that live on land spend their nights in the hollow of a tree, a burrow that they dig, or some other hiding place. Many of them enter the water at times and are good swimmers. A few, such as the Nile monitor and Merten's water monitor, only come out of the water to sunbathe, or bask, on shore. The females also leave the water to dig holes along the shoreline, where they lay their eggs.

Many species in this family hide themselves when they hear people coming, so people often see little but their footprints. When they cannot hide, these lizards will defend themselves. They will typically flatten out from side to side and puff out their cheeks, which makes them look larger. A few even stand up on their hind legs. They also hiss. Some of the larger species can be quite dangerous, because they can swing their tail around with great speed and use it as a whip to strike the attacker. The Komodo dragon is large enough to kill humans with bites from its powerful jaws.

During the breeding season, males will fight over females. Their fights are wrestling matches in which two males stand belly to belly, grip each other with their arms, and try to knock one another down. Smaller species wrestle while lying on the ground. The winning male then courts the female by flicking his tongue over her snout and body. After mating, the females lay eggs in underground burrows, occasionally dug in the middle of termite nests or ground-built bird nests. Depending on the species, she may lay two to sixty eggs. The smallest species lay the fewest eggs, and the largest lay the most.


These lizards are usually shy animals that hide when people approach. For this reason, people usually do not see them. The footprints they leave behind, however, usually provide enough clues to tell which species recently passed by. Monitor lizards are often mentioned in ancient tales and are likely the basis for legends of dragons. Some humans now hunt them for their skin, which is highly prized as leather.


The Komodo dragon is the heaviest lizard on Earth today, but it is only half as long and weighs just one-quarter of the amount of its ancient relative, known as Megalania prisca. This enormous lizard tipped the scales at more than 1,320 pounds (600 kilograms), compared to the Komodo's 330 pounds (150 kilograms). While a Komodo can grow to an impressive 10 feet long (3 meters), Megalania prisca grew to at least 20 feet (6.1 meters) from snout to tail tip. Some people believe it may have even reached 30 feet (9.1 meters) or more. Now extinct, the lizard lived until at least 19,000 years ago.


According to the World Conservation Union (IUCN), two species are Vulnerable, which means they face a high risk of extinction in the wild. These are the Indonesian Komodo dragon and the Philippine Gray's monitor. Their low numbers are due mainly to habitat loss and to hunting. People kill these lizards for their skin. The U.S. Fish and Wildlife Service lists the following four species as Endangered, which means that they are in danger of extinction throughout all or a significant portion of their range: the desert monitor, the Indian monitor, the Komodo dragon, and the yellow monitor.


Physical characteristics: A thick-bodied animal, the Komodo dragon is the world's heaviest lizard. It can reach a weight of 330 pounds (150 kilograms) and a length up to 9.9 feet (3 meters) from snout to tail tip.

Geographic range: They live on a few Indonesian islands, including Komodo.

Habitat: Komodo dragons can live in dry or moist habitats and are good enough swimmers to spend some time in the water.

Diet: They are meat eaters, dining on deer, pigs, other mammals, lizards, and birds. The juvenile diet includes insects, bird and turtle eggs, and carrion.

Behavior and reproduction: Komodo dragons are active during the day, when they do their hunting. They either walk around looking for food or hunt by ambush. Juveniles are good climbers, but adults are too large to climb and stay on the ground. The mating season runs from May to August. In September, the females begin laying their eggs in burrows. The average nest contains about eighteen eggs, but some females can lay as many as three dozen at a time. The young hatch in March and April. When they reach eight or nine years old, they are ready to mate and become parents themselves.

Komodo dragons and people: Most people know of Komodo dragons from the zoo. Humans may find use for these lizards, because their blood contains special substances, called antibodies (AN-tee-BA-dees), that may someday help fight health problems in people.

Conservation status: Because the number of Komodo dragons is small, and they live in a very small area where their habitat is disappearing, the World Conservation Union (IUCN) considers these lizards to be Vulnerable, which means that they face a high risk of extinction in the wild. The U.S. Fish and Wildlife Service considers the lizards to be Endangered, which means that they are in danger of extinction throughout all or a significant portion of their range. ∎


Physical characteristics: The crocodile monitor is a long-tailed, yellow-spotted lizard that may grow to 12 feet (nearly 3.7 meters) in length from snout to tail tip, although some claim that the lizards may reach 15 to 19 feet (4.6 to 5.8 meters) long. It is often considered to be the world's longest lizard.

Geographic range: This lizard lives on southern New Guinea.

Habitat: The crocodile monitor frequently climbs into trees of the rainforest.

Diet: They probably eat birds in the wild, but in captivity, they also eat mice and rats.

Behavior and reproduction: Crocodile monitors spend much of their time in trees where they look for food. When they feel threatened, they will swing their tails like whips to strike an attacker. During mating season, the males wrestle one another. Females lay eggs, which hatch into large babies that can be 20 inches (0.5 meter) in length.

Crocodile monitors and people: Legends among the native people of New Guinea claim that this lizard is an evil spirit that breathes fire and eats men.

Conservation status: The crocodile monitor is not considered endangered or threatened. ∎



Auffenberg, W. The Behavioral Ecology of the Komodo Monitor. Gainesville: University Press of Florida, 1981.

—— The Bengal Monitor. Gainesville: University Press of Florida, 1994.

—— Gray's Monitor Lizard. Gainesville: University Press of Florida, 1988.

Badger, D. Lizards: A Natural History of Some Uncommon Creatures— Extraordinary Chameleons, Iguanas, Geckos, and More. Stillwater, MN: Voyageur Press, 2002.

Bennett, D. Monitor Lizards. Natural History, Biology and Husbandry. Frankfurt am Main: Edition Chimaira, 1998.

King, D., and B. Green. Goannas: The Biology of Varanid Lizards. University of New South Wales Press, 1999.

Murphy, J. B., C. Ciofi, C. de la Panouse, and T. Walsh, eds. Komodo Dragons: Biology and Conservation. Washington, DC: Smithsonian Institution Press, 2002.

Pianka, E. R., and L. J. Vitt. Lizards: Windows to the Evolution of Diversity. Berkeley: University of California Press, 2003.


Mealy, Nora Steiner. "Creatures from Komodo." Ranger Rick (August 2001): (accessed on October 18, 2004).

Web sites

"Crocodile Monitor." Honolulu Zoo. (accessed on October 18, 2004).

"Komodo Dragon." Enchanted Learning. (accessed on October 18, 2004).

"Komodo Dragon." Honolulu Zoo. (accessed on October 18, 2004).

"Komodo Dragon, Varanus komodoensis, 1998." San Diego Zoo. (accessed on October 18, 2004).

"New Guinea Crocodile Monitor." Central Florida Zoo. (accessed on October 18, 2004).

"Varanus komodoensis." Animal Diversity Web. (accessed on October 18, 2004).

"Varanidae." Animal Diversity Web. (accessed on October 18, 2004).