Nile Monitor Lizards: Invasive Species in Florida Threatens Native Species

Nile Monitor Lizards are Not Native to Florida: Photo by Dennis Busy

The Nile Monitor (Varanus niloticus) is one of the many non-native invasive species plaguing Florida. These reptiles are a serious threat to native animal species in all state habitats. The first of these aggressive and powerful lizards was found in the wild in 1981, followed by the discovery of an established (breeding) population in 1990. Since then, their numbers in the wild have been increasing steadily throughout the state.

Introduction of Nile Monitors to Florida Habitats

Nile Monitors were originally brought to this country from their native habitats in southern and central Africa as part of the exotic pet trade. Their introduction into the wild is most likely due to escapes or intentional releases by owners who could no longer handle them. These big semi-aquatic lizards may grow to over seven feet (2.42 meters) in length and weigh as much as 20 pounds (10 kg).

The increase in wild population of this invasive species is primarily a result of females laying as many as 60 eggs at a time. Eggs are laid in sand or dirt nests located near water. A female abandons the nest after depositing her eggs, relying on sunlight to incubate the eggs. Gestation typically takes four to six months.

When babies hatch, normally during the months of February through April, they immediately head for the protection of water near the nest. The apparent successful reproduction rate of this invasive species has increased the number of sightings and captures of Nile Monitors in Florida over the past 10 years.

Closeup of a Monitor Lizard: Photo by James Hearn

Why These Intelligent Reptiles are a Problem

These intelligent lizards create a problem for native species because their diet includes invertebrates, endangered burrowing owls, insects, carrion, fish, young alligators, young American crocodiles, snakes, turtles, and any terrestrial or aquatic vertebrate they can overpower. They are especially a threat to native egg laying animals such as birds, turtles, and alligators. Nile Monitors dietary preference is a nest filled with eggs or new born young.

Known for their sharp teeth and bad tempers, Nile Monitors are excellent swimmers and are not limited to any specific habitat. Their known range extends from the Florida Keys to the northern portions of the state. They are found in the Everglades, Cape Coral, Sanibel Island, Tampa Bay, and Key Largo

The range of this invasive species is likely to expand beyond Florida’s borders, because these reptiles hibernate during cold months. The limit of their range is unknown; however, their ability to adapt to most habitats may extend their range into bordering southeastern states.

Click to Read Page Two: Controlling Nile Monitor Lizards in Florida

© Copyright 2011 David R. Wetzel, Ph.D., All rights Reserved. Written For: Decoded Science
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  1. Alex says

    That photo you have is not of a Nile monitor at all. The first photo is of an Ornate monitor Varanus Ornatus which are perfectly legal in Florida. The second photo although not labeled as any specific species is a juvenile komodo.dragon. Kind of strikes me as odd that there are no actual photos of the correct species in the article. I’ve noticed that this tends to be the case with nearly every article on Nile monitors invading Florida. I don’t think many people realize that there are 70+ species of monitor worldwide. . To single out the Nile monitor and ignore all the other species of monitor invading Florida is absurd.

  2. Michael Kirsten says

    It’s not Always the Owners Fault!
    They Were Probably Set Loose When a Hurricane Hit Florida.Why Kill Them?
    I Own a Tame Female 5 foot Asian Water Monitor.She is both Very Curious and Intelligent. I Plan To Keep Her My Whole Life.I Know They Can Become Great Pets Because Like a Dog,My Lizard wears a Leash and Collor and Likes to Walk Around.I Have worked with reptiles for 14 Years and I am Part of the Reptile Club North Bay Herpetelogical Society.
    I Believe They Shouldn’t Be Killed Because It Wasn’t Their Fault.
    There Are Too Many Dogs and Cats,So Many That Most Are Just Put Down.These are Intelligent Reptiles and I Believe We Can Find Another Solution Without Killing Them!!!

  3. Graeme says

    Please if you capture any monitor lizards send them to me for my reptile breeding centre in South Africa.They’ll be used mainly to educate people and only ever keep in captivity.And never sold if breed outside of africa’s border.I’m stricked here at My “Tribal Reptile Breeding centre”that if you are deamed sutable to purchase one or more from me.That my stricked laws pertaining to the keeping of them are strickly adhered to.Here we need permits for them.I’ll go a step futher by taging each one recieved saterlite tracking responders.This is to insure none make there way outside the South African boarders.And any one trying to move them accross the South African boarders will be dealt with by the full extent of the law.

  4. RW Akile says

    We have Monitor Lizards here in Southern California as well. One at least has been living in the Baldwin Hills Area of Los Angeles. Luckily this one may be the ONLY one in its area. That does not count the possibility that one or some may well be living in the foothills adjacent to Los Angeles. Luck is it’s too cold in the mountains to sustain the reptiles found in Florida. The Coastal mountains are another story. Weather is mild never too cold or too hot.


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