Photographer:Bluemoose Affiliation: www.commons.wikimedia.org Copyright:CC BY-SA 3.0
Varanus niloticus can average lengths of 23-32 inches but can reach up to 8 feet long and weigh over 22 pounds! Like all monitors, they have long neck and tails with a forked tongue that is also blue. The head is narrow and wedge-like and shorter than the neck. Overall, they are gray-brown or olive green. The jaws and head have cream-colored stripes that become chevrons on the neck. Also, there are six to nine bands of yellow dots that encircle the body of the Nile monitor. Juveniles are more brightly patterned than adults. Varanus niloticus has large, strong claws for digging and a muscular tail that ideal for swimming and is usually 1.5 times longer than the body.
Nile monitors are potentially the most destructive lizard introduced to Florida. They have had negative effects on the American alligator (Alligator mississippiensis) but especially the American crocodile (Crocodylus acutus) because they have diets similar to them; but also, they are major predators of crocodilian eggs and hatchlings. Also, they have a tendency to occupy burrows that displace endangered animals like the Burrowing Owl (Athene cunicularia) and the gopher tortoise (Gopherus polyphemus) and eat the native animal’s eggs. Should the Nile monitor make their way south to the Florida Keys they could make four species or rodents extinct. Their generalist and ravenous appetite makes them a threat to native fauna.
All lifecycle information is based on the Nile monitor’s from Africa and may or may not be 100% applicable to Nile Monitor populations in Florida. Females are sexually mature in two years and they breed every other year; so any given year only 50% of the females are breeding and laying eggs. During the summer females feed and accumulate fat to then lay eggs in the winter dry season in active termite mounds. Eggs clutches are about 35 eggs and smaller female Varanus niloticus will lay fewer eggs than larger females. Hatchlings emerge 6-10 months later, near the beginning of the wet season and are 6-12 inches in length. Varanus niloticus can live more than 10 years in the wild.
Free-living Nile monitors were first spotted at Cape Coral in 1990; presumably as a result of the pet trade. By 2002 Varanus niloticus was found all along the Atlantic coast of Florida and the southern part of the peninsula. Since the Nile monitor thrives in temperate parts of Africa Varanus niloticus could establish itself as far north as both Carolinas.
Forests and savannas of Africa
U.S. Present: FL
U.S. Habitat: Adapted for both terrestrial and aquatic habitats but they prefer to be near permanent bodies of water. Florida’s mangrove swamps have become an ideal habitat for Varanus niloticus.
Once established, Varanus niloticus is very difficult, if not impossible to eradicate. Population reductions and prevention of further infestation are the main management strategies. Monitors may be captured with nooses or live traps or by digging them out of the ground. Arboreal hatchlings can be caught at night by hand. Thankfully, now there are regulations that prevent monitors from being purchased by casual, untrained pet owners.
Enge, K. M., K. L. Krysko, K. R. Hankins, T. S. Campbell, and F. W. King. 2004. Status of the Nile monitor (Varanus niloticus) in southwestern Florida. Southeastern Naturalist 3:571-582.
Faust, R. J. 2001. Nile monitors: everything about history, care, nutrition, handling, and behavior. Barron's Educational Series, Hauppauge, New York. 95pp.
Mauldin, R. E., & Savarie, P. J. 2010. Acetaminophen as an oral toxicant for Nile monitor lizards (Varanus niloticus) and Burmese pythons (Python molurus bivittatus). Wildlife research, 37(3), 215-222.
Pernetta, A. P. 2009. Monitoring the trade: using the CITES database to examine the global trade in live monitor lizards (Varanus spp.). Biawak, 3(2), 37-45.