Monitor Lizards: Habitat, Diet, Size, and Species Guide

Monitor lizards are highly adaptable reptiles that occupy many different environments. Their ability to thrive in rainforests, deserts, savannas, and coastal regions has contributed to their wide geographic range.

Some monitor species live primarily in trees, others are ground dwelling, and several are semi aquatic, spending much of their time in and around water.

When cornered or threatened, monitor lizards will often turn sideways to present a larger profile. They may puff out their necks and hiss to warn potential threats.

If an intruder gets too close, a monitor lizard can use its tail as a whip. With a single, well-aimed swing, the tail can deliver a painful strike.

Monitor lizard tails are extremely strong and do not exhibit caudal autonomy, which is the ability to drop the tail when grabbed, as seen in tegus and iguanas.

In fact, some tree dwelling monitors, such as the brightly colored green tree monitor, have prehensile tails that allow them to grip branches for added support and balance.

Kimberley rock monitor (Varanus glauerti)

A few monitor species are omnivores or even largely frugivorous, feeding on fruit, but most monitor lizards are carnivores.

Their diet varies based on size and habitat. Smaller species, such as the Kimberley rock monitor (Varanus glauerti), primarily feed on insects. Semi aquatic species feed on fish and crustaceans. Larger land dwelling and arboreal species feed on reptiles, birds, and mammals.

Eggs are considered a delicacy by many monitor species. Smaller eggs are often swallowed whole, while larger eggs may be crushed in the jaws so the contents can be consumed.

There is a long-standing story that explains how monitor lizards received their name. Several species, such as Nile monitors in Africa and water monitors in Asia, patrol riverbanks searching for crocodile nests to raid for eggs.

Early civilizations relied heavily on river water for daily life. People observed that when these lizards suddenly fled the shoreline, it often signaled the return of crocodiles to their nests. In this way, the lizards acted as “monitors” of danger.

When it comes to feeding, monitor lizards are capable of swallowing large prey whole. Even animals slightly larger than their head can often be consumed due to flexible jaws and strong throat muscles.

Monitor lizards range dramatically in size, from very small insect eating species to massive apex predators.

Dampier Peninsula Monitor

The smallest of all monitor species is the Dampier Peninsula monitor (Varanus sparnus). This species is found only in the Dampier Peninsula of Western Australia.

These active lizards inhabit semi-arid rocky areas and grow to only about 9 inches in length. Due to their small size, they feed primarily on insects.

Savannah Monitor

Savannah Monitor (Varanus exanthematicus)

One of the most commonly kept monitor species is the African savannah monitor (Varanus exanthematicus). These lizards are often imported at low prices, which unfortunately leads to many being kept without proper care.

Savannah monitors require large enclosures and high temperatures. They are native to the dry savannahs of Africa, where temperatures can reach 100 degrees Fahrenheit. Although they grow over 3 feet in length, their natural diet consists mainly of invertebrates. Feeding captive savannah monitors mice and rats for enrichment can be beneficial. However, caution should be exercised to avoid overfeeding, as large quantities of rodents can lead to obesity and poor health.

Nile Monitor

Nile Monitor (Varanus niloticus)

Another African monitor once commonly imported as a pet is the Nile monitor (Varanus niloticus). Nile monitors are large, powerful, semi aquatic lizards that can reach 6 feet in length.

Wild caught individuals were typically nervous and defensive. As they grew larger, they were capable of inflicting serious injuries.

Asian Water Monitor

Asian Water Monitor (Varanus salvator)

The Asian water monitor is the second largest lizard species by mass. These monitors can reach lengths of up to 8 feet and weigh nearly 100 pounds.

They are semi aquatic and require large areas of both land and water. Their diet includes fish, crustaceans, rats, and other prey. Native to Southeast Asia, Asian water monitors have even been observed swimming in the ocean.

Komodo Dragon

Komodo Dragon (Varanus komodoensis)

The largest living lizard is the Komodo dragon (Varanus komodoensis). These massive reptiles can grow over 10 feet in length and weigh more than 300 pounds.

Komodo dragons are found only on the island of Komodo and a few nearby islands in Indonesia. For many years, their bite was believed to be deadly due to harmful bacteria. Research completed in 2013 confirmed that Komodo dragons are venomous, and that venom plays the primary role in incapacitating prey.

Many monitor lizard species are impacted by habitat loss and wildlife trade. Responsible education, conservation efforts, and habitat protection are important to ensure these reptiles continue to thrive in the wild.