Nile Monitor Lizards: Invasive Species in Florida Threatens Native Species


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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.

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