From Human Food Waste to Prey: What Monitor Lizards Really Eat

Monitor lizards are a genus of large lizards found in Africa, Southern Asia, and Australia. There are 80 recognized species of monitor lizards, including the Komodo dragon, Asian water monitor, and the Nile monitor. Although most monitor lizards are venomous, their venom is not deadly and is used only to subdue their prey. What does their prey consist of? What do monitor lizards eat? Continue reading to discover these answers and more.

Scavengers, Carnivores, and Insectivores

Monitor lizards are scavengers, carnivores, and insectivores. Across the 80 species of monitor lizards in the genus Varanus, there are variations in their diet. Though most will eat whatever is abundant and available, there are exceptions. Gray’s monitor (V. olivaceus) and the Northern Sierra Madre forest monitor (V. bitatawa), both native to the Philippines, eat a fruit-based diet. In areas with heavily concentrated human populations, scientists are discovering that some monitor lizards have diets that consist primarily of human food waste. In a study in Malaysia, scientists observed a group of 20 Asian water monitors (V. salvator), which they hypothesized were responsible for raiding sea turtle nests. What they discovered was quite interesting. While the monitor lizards were responsible for raiding the nests (21.2% of their stomach contents were turtle eggs or hatchlings), the majority of their stomach contents was human food waste (76.8%).

Diet

Whether their prey is already dead when they find it or they hunt it themselves, monitor lizards eat a variety of foods. Based on their location, monitor lizards will eat:

• carrion
• insects
• reptile eggs
• birds
• snakes
• toads
• lizards
• crustaceans
• turtles
• pigs
• deer
• cattle
• water buffalo
• fruit and berries

Hunting Techniques

Monitor lizards use a variety of methods to hunt and obtain food. Sometimes they actively hunt for food during the day. Other times, they will wait patiently to catch prey as it passes by. Monitor lizards also raid the nests of other reptiles. The Nile monitor (V. niloticus) has been observed working in tandem, with one distracting a female crocodile to lure her away from her nest so that the other may steal her eggs. However, the monitor’s principal technique is to search for carcasses of dead animals and feed on the remains.

How Monitor Lizards Use Venom

Though monitor lizards are venomous, their venom is not deadly like that of some snakes and spiders. Most species of monitor lizards have venom glands in the lower jaws. They do not have fangs. Instead, monitor lizards mix their venom with saliva, which is delivered in a bite from their sharp, blade-like teeth. Their venom contains either anticoagulant properties, which inhibit the clotting of the prey’s blood, or neurotoxins, which can lead to paralysis. For example, Komodo dragons (V. komodoensis), which have anticoagulant venom, attack their prey and wait for it to bleed to death.

Monitor Lizard Predators

The main predators of the adult monitor lizard are humans, wild cats, and large crocodiles. Humans hunt the lizards for their skins and their flesh. Juvenile monitor lizards face a variety of predators, including birds, snakes, mammals, and other carnivorous reptiles.

Monitor Lizards and Human Interactions

Monitor lizards are not out to cause trouble and prefer to keep to themselves. However, if they are provoked, they will attack. Because monitor lizards have sharp teeth and their mouths are full of bacteria, while a bite may not be life-threatening, one can quickly become infected. Humans who have been bitten by a monitor lizard need to seek medical attention promptly.