Green Tree Monitor

Green Tree Monitor

Green Tree Monitor

© AMNH / Denis Finnin

High in its treetop habitat, the slender Green Tree Monitor hangs out and hides among the leaves.


This active, largely tree-dwelling species uses its long agile tail as a fifth limb. That long tail, along with its long tongue and slim body, give this monitor a snakelike look. Many scientists consider monitors to be close relatives of snakes.


Monitors have keen vision. They are active in the daytime, so their pupils--the opening where light enters the eye--are large and round.

Limbs and Feet

The Green Tree Monitor's long limbs, long toes and long claws are all useful when it climbs trees. Its agile tail helps, too.

Upper Jaw

This upper jaw can move independently from the skull. Most squamates have that ability, but it is highly developed in monitors. It helps the animal move prey into a better position for swallowing.

Third Eye

This white spot is the so-called parietal eye, an opening that allows light to reach the pineal organ in the brain. Many lizards have these "eyes," which have a basic lens and retina but don't form images. Third eyes probably increase sensitivity to light and dark, helping to regulate the lizard's wake/sleep and basking cycles.

Meet the Family

This family, Varanidae, includes about 60 species. They differ in size and color pattern but are alike in shape. Most Monitors live in Australia--their name there, "goannas," comes from the word "iguana"--with only a few species in Africa and Asia. Large monitors are often the top predators in their environments.

A Komodo dragon eating prey.

Komodo dragon (Varanus komodoensis)

© Fred Bruemmer/DRK Photo

Komodo Dragon
Varanus komodoensis

Deer are among the Komodo Dragon's favorite prey. But Komodos will kill and eat anything they can overpower, including humans. With a top speed of 20 kilometers (13 miles) an hour, and the intelligence to predict a victim's escape route, Komodos seldom go hungry.


A Yellow spotted monitor standing upright on its hind limbs on a dirt surface with scrubby brush and trees in the background.

Yellow spotted monitor (Varanus panoptes)

© Robert Valentic /

Yellow Spotted Monitor
Varanus panoptes

Some monitors stand upright in response to a threat or to get a better look around.

Fast Facts

NAME: Green Tree Monitor; Varanus prasinus
SIZE: 1 meter (3 feet)
RANGE: New Guinea
DIET: Small mammals, arthropods