What to Know About Monitor Lizards

Medically Reviewed by Vanesa Farmer, DVM on November 18, 2022
5 min read

Monitor lizards are a large group of lizards that fall under the genus Varanus. There are many different types, and they vary widely in size and appearance. Monitor lizards are not native to the Americas and are seen as invasive species in the US. Here’s what you need to know about monitor lizards, including what they eat, where they live, and if they make good pets.

A monitor lizard can be any lizard that is a member of the Varanidae family. They can belong to either the genera Varanus or Lanthanotus. Since there are a number of different monitor lizards, they can vary in appearance. In general, most monitor lizards have a heavy body with a long tail and well-developed legs. These lizards have long heads and necks. Like many reptiles, they have long, forked tongues that resemble those of a snake.

Monitor lizards, known as goannas in some parts of the world, first appeared during the Miocene epoch about 15 million years ago. Fossils of an extinct species of monitor from the Pleistocene epoch show that the largest of these lizards could grow to be 7 meters long and weigh 600 kilograms.

Modern monitors are smaller than some of their ancestors were. The smallest monitors are only about 20 centimeters long, while the largest, the Komodo dragon, can grow to be 3 meters long. On average, most monitors range between 1 to 3 meters long from tip to tail.

A monitor lizard’s coloring depends on its environment and where it’s from. Monitors that are native to desert climates are normally orange or yellow, while those that live near water or in trees are dark. Some have spots, speckles, or bands on their skin depending on their age or species.

Monitor lizards are native to a number of different areas, depending on the species. In general, these lizards like warm climates and enjoy basking in the sun. Some species burrow in the ground near water or along the banks of canals. Most prefer a somewhat aquatic habitat and can handle cooler temperatures, but other species opt for semi-tropical weather.

Monitor lizards are found in the wild on several different continents. In Africa, monitors live mostly in the Sahara but can be found all across the continent except in the northwest. Several species live in Australia and on islands throughout the southwest Pacific Ocean. Monitors live all across southern and southeastern Asia, including on several islands.

Monitor lizards aren’t native to the US, but are now listed as an invasive species in parts of Florida. The Nile monitor was introduced around 1990, most likely as part of the exotic pet trade. It’s believed that some of them probably escaped or were released into the wild around this time. While monitors were initially spotted in the Miami area and around southwest Florida, their range has been expanding to other parts of the state.

Most monitor lizards are carnivores and will eat just about anything. Their bodies are adapted to make them really good predators both in water and on land. Their long tails act like a rudder to help them glide through the water. This makes them really good swimmers and they’re excellent at catching fish to eat, as well as other sea animals like mollusks and turtles.

On land, monitor lizards will eat anything that they can trap and swallow. They have long claws and can move surprisingly quickly, so they have a variety of prey to choose from. What they hunt depends on the size of the lizard. They will eat:

  • Insects
  • Crabs 
  • Eggs of birds or other reptiles
  • Small reptiles
  • Spiders
  • Mammals 
  • Birds
  • Amphibians

Monitor lizards will also scavenge for carrion or the leftovers from another animal’s prey. They are attracted to the smell of rotting flesh. While most monitors try to take on prey within their own size range, one monitor lizard, the Komodo dragon, can take down prey that’s as large as water buffalo.

Even though most monitors live on a primarily carnivorous diet, some species also eat fruit. The Gray’s monitor eats mostly meat but supplements its diet with fruit. From research, the Northern Sierra Madre forest monitor lives on mostly fruit but will eat some meat.

There are almost 50 species of monitor lizards in the Varanidae family. 27 of these live in Australia alone. Within these species, there are different types of monitors, such as water, semi-aquatic, or tree monitors, depending on their preferred place to live.

Tree monitors like to live high up in the treetops of swamps and tropical forests. From this vantage point, they can look down on their surroundings below and keep an eye out for prey. They have really sharp vision and can move down the trees quickly with their sharp claws.

Semi-aquatic monitors spend some time in the water and some time on land. They make burrows that they sleep in during the daytime. Aquatic monitor lizards are really good swimmers and can stay under the water for several minutes without needing to come up for a breath.

Many people enjoy having reptiles, including lizards as pets. There are both pros and cons when it comes to having monitor lizards as pets. One of the good things is that they’re not picky about what they eat, so it’s easy to feed them a variety of different things. Monitors are also solitary, so they don’t need another animal to keep them company.

On the downside, monitor lizards grow very quickly, so you need to have enough space to let them live comfortably. As they grow, they will need more and more food, so that can start adding up quickly and become quite expensive.

Keep in mind that monitor lizards are wild animals and can be pretty aggressive. They have sharp claws and a lashing tail that they are not afraid to use when they feel threatened. As pets, monitor lizards are known to bite children or other small housepets.

If you do decide to get a monitor lizard as a pet, check to see if your state or town has any regulations in place, such as needing a permit. Never attempt to take a monitor lizard in the wild as a pet. If you see a monitor lizard on your property, you should call animal control so they can handle it, as they are an invasive species.