Monitor lizards of the Varanus genus, including the Nile monitor (Varanus niloticus), have captivated reptile enthusiasts for generations. The herpetological community has made significant strides in understanding captive care and breeding. While aspects like housing can be challenging, particularly with larger species, providing ample space without compromising security remains a straightforward principle. Feeding, however, presents more complex questions: What to feed? How much? How often? And what about supplements? While current literature on monitor husbandry is generally reliable, older publications may contain outdated information. It's crucial to remember that monitors are a diverse group, with individual species having unique dietary needs. This article compiles data from various experts and personal experiences, acknowledging that monitor nutrition is a debated topic. Always research the specific needs of your monitor species, as some have very specific dietary requirements, while others are less discriminating.
Nile Monitor Overview
The Nile monitor is a large lizard native to Africa, known for its impressive size, semi-aquatic lifestyle, and carnivorous diet. Nile monitors are olive green to black in color and have cream-colored or yellow stripes on the jaw and head. They have rows of yellowish, V-shaped stripes beginning at the base of the skull and neck which transform into bands or spots along the back. Nile monitors may be observed basking on rocks and branches and are often seen in or close to water. They are mostly active during the day. At night they may sleep on branches or submerged in water in warm weather or retreat to burrows in cooler weather. Nile monitors are skillful climbers and adept swimmers. Nile monitors are not recommended for novice reptile keepers due to their large size, powerful build, and potentially aggressive nature. They require specialized care, a secure environment, and a significant commitment from their owners.
Physical Characteristics
Nile monitors share common features with other monitor lizards, including a robust physique and a forked tongue. Their strong claws and muscular legs aid in climbing trees. Distinct features include a bowed lower jaw, an elongated snout, and blunt, strong posterior teeth, enabling them to consume hard-shelled prey like mollusks. A defining characteristic is their long, laterally compressed tail, often longer than their body. Juvenile Nile monitors exhibit bright yellow and black patterns on their skin. As they mature, their heads and backs become olive-brown or greenish-brown, while black bars appear on their throats and bellies.
The Nile monitor is one of the largest lizard species in Africa and can attain lengths of about 6.5 feet and weigh up to 17.8 pounds, although a typical adult averages 5 feet in length and weighs close to 15 pounds. The species usually ranges in size between 100 cm and 140 cm (tail included). It can, however, reach up to 200 cm in length. In comparison, the hatchlings are quite small, with a weight of 26 grams and a length of 30 cm.
Habitat and Behavior
Nile monitors inhabit various environments, including swamps, woodlands, evergreen thickets, mangroves, scrubs, and dry savanna. As excellent swimmers, they prefer proximity to water sources like pans, rivers, and lakes, but they are also skilled climbers, adapting well to terrestrial life. In the wild, they are often found on overhanging branches above water during the day, seeking shelter in burrows at night.
Read also: Water Monitor Feeding Habits
Female Nile monitors reach sexual maturity at about 2 years or when they attain lengths of about 14 inches. Eggs are typically deposited into burrows, and clutches consist of 12-60 eggs depending on the size of the female, with larger females laying more eggs. Males will mate with many different females and engage in fierce wrestling competitions with other males for mating opportunities. Nile monitors can live up to 20 years in captivity.
Dietary Needs in the Wild
Nile monitors are opportunistic predators with a broad diet. They hunt for prey on the surface, below ground, in trees, and in both fresh and saltwater. Their diet includes:
- Fish
- Frogs and toads
- Insects (beetles, caterpillars, termites, grasshoppers, and crickets)
- Rodents
- Crabs, crayfish, mussels, snails, and slugs
- Earthworms and millipedes
- Spiders
- Birds and their eggs
- Other reptiles (lizards, turtles, snakes, young crocodiles)
- Small mammals
Nile monitors have huge appetites. They are one of Africa's most voracious predators. Because this species has adapted to eat a variety of food in the wild, if you keep one as a pet, you should ensure they get a varied and balanced diet.
Feeding Nile Monitors in Captivity
Mimicking the wild diet of Nile monitors in captivity is essential for their health and well-being. A varied diet helps ensure they receive all the necessary nutrients.
Food Items
Some of the foods you can feed them include:
Read also: Ackie Monitor: Diet and Care
- Insects (like well-fed crickets)
- Worms (mealworms, butterworms, waxworms)
- Fish
- Cooked eggs
- Raw beef heart
- Canned monitor or dog food (use sparingly)
- Pre-killed rodents like rats and mice
While Nile monitors eat live prey in the wild, it’s best to feed them pre-killed foods to avoid putting your pet at risk of being bitten.
Feeding Frequency and Portion Size
The frequency and the type of food you feed your monitor will depend on its size. For example, small, young monitors need smaller foods every day, while large adults need bigger foods a few times a week. Niles are almost always hungry and fare best if fed measured portions once daily, although babies can be offered as much as they will eat per feeding. For adults, feed an amount roughly equal to the volume of the monitor’s head every 2 days. Excess food can lead to obesity in adults.
Supplementation
Depending on what your vet suggests, you may need to give them vitamin supplements weekly and calcium supplements two times a week. Growing monitors benefit greatly from the use of calcium and vitamin supplements in their diets. Some argue that if fed a varied diet of whole animal prey, monitors will not face any related health issues. Baby and juvenile monitors should have their food dusted with a high quality calcium/vitamin D3 supplement at every feeding. In conjunction with a suitable source of full spectrum lighting, these supplements will allow for proper skeletal growth and muscle development. In addition to the calcium supplement, a multivitamin is highly recommended. This should be in the form of a powder that is designed specifically for reptiles.
Foods to Avoid or Limit
Foods designed for other types of animals (or humans) should be avoided or fed sparingly. These include cat and dog foods, hot dogs, and red meat.
The Rodent Debate
The debate over whether or not to feed rodents to captive monitors is a heated one. In all likelihood, there is probably not a right or wrong answer. For many monitor keepers, watching their mini-dinosaurs hunt down and devour a live mouse is all part of the thrill. Mice and rats are generally considered to be too high in fat for most captive, exercise-deprived monitors. Keepers who choose to raise their monitors on a rodent-only or mostly rodent diet should be encouraged to avoid unweaned mice, as they have little or no calcium, and are fairly deficient in other vital nutrients. It should be noted that rodents are not a completely bad food source. In fact, they are an important part of a balanced diet. It is widely accepted to feed only pre-killed rodents to monitors. Live mice and rats can easily injure the animal they are intended to feed, resulting in lacerations, infections, or abbesses.
Read also: Savannah Monitor Feeding
Alternative Diet Options
Keepers who have been working with monitors for any length of time may be aware of this dietary option, while it's existence may come as news to less experienced hobbyists. Quite a few years ago, keepers and animal nutritionists at the San Diego Zoo were experimenting with non-rodent diets for their larger monitor species. The exact, original recipe is not really known, but it is widely accepted that it contained nothing more than raw, ground turkey, eggs, steamed bone meal (as a source of calcium), and multivitamins. I recommend mixing one pound of raw, ground turkey with two raw eggs including the shells. The steamed bone meal is easily replaced by one heaping tablespoon of a high quality calcium/vitamin supplement designed specifically for reptile use. Mix this well, and feed your lizard whatever it will consume in a few moments. We have had tremendous success (as did the San Diego Zoo) with this diet, and provide it to all of our monitor and tegu species regularly.
General Care Considerations
Suitability as Pets
Nile monitors usually live from 10 to 20 years in captivity, something to consider when deciding whether this reptile is a suitable pet for you. They may live a long time, but they do not make friendly pets. Known to be hostile, Nile monitors don't hesitate to bite their owners when stressed or cornered. If you raise one from the hatchling stage, you may be able to trust them a little. But even then, they may resist your attempt to tame them and should be treated with caution. If you ever see them standing on their legs, hissing and flicking their tails, this means they feel threatened and are about to attack. They might also emit a foul-smelling odor to deter you or whoever they assume to be their attacker. Nile monitors are known to scratch their owners' faces when agitated. So, it's best to avoid getting one as a pet if you have young kids at home. Also consider your finances, because owning such large lizards can get expensive. Not only do these animals need to be fed large prey several times a week, they require a custom-built enclosure with a large water source where they can swim, run, climb and grow to their adult size. You need to ensure that the enclosure is secure enough that they can't escape by burrowing or climbing out. If you like reptiles but don’t have experience with them, think twice before getting a monitor. They don't make friendly or obedient pets. Also, check your local legislation to find out if you’re allowed to keep exotic pets in your area.
Handling
Because of the less-than-friendly personalities of these lizards, it is hard to hold them without being bitten. It's best to start working with them while they're still young and small. If you handle them frequently with care and a lot of patience, you may gain their trust over time.
Enclosure
Nile monitors need large, open areas - similar to their natural habitat - to thrive in captivity. As the substrate, you can use the land, sand, or crushed bark. The room must be objects, creating suitable habitat, such as rocks, tree trunks, artificial plants or hollow logs. Cover their floors with orchid bark or pine shavings and scatter rocks and hollow logs across the area to give the enclosure the look and feel of natural woodland.
Hatchlings can start off in tanks 3’ long with secure screen tops. After 6 months they need enclosures of at least 4’ x 2’. Adults (2-3 years old) require an enclosure the size of a small room, at least 12’ x 4’ for monitors under 48 inches in length and at least 15’ x 5’ for specimens exceeding 48”. Juvenile monitors should be provided with shelters in which they can curl their entire body. Adults should be offered plastic doghouses or the top half of large dog carriers. Many monitors use their shelter for sleep. Others will spend the night on tree branches or in their water container. Flat rocks are required for nail wear. If rocks are placed alongside the water container, nails will wear as the lizards enter and exit the water.
Water
Need a container of water large enough to lizard could swim. Nile monitor lizards have a habit of defecating in the water, so the water should be changed immediately after the contamination, or at least daily. Accessible water tubs large enough for complete immersion are required. For small individuals, reptile water dishes, dog bowls and plastic storage containers suffice. For adults, plastic cement mixing tubs or plastic kiddie pools are required. Nile monitors kept singly usually defecate in their water container.
Temperature and Lighting
Nile monitors need sunlight. Make sure their enclosures get unfiltered natural sunlight. Otherwise, use UV radiation/full spectrum fluorescent reptile lights. Regularly check the enclosure temperature and make sure it is in the range of 80ºF to 90°F during the day and 78ºF to 80°F at night. Daytime temperature range for Nile monitor should be about 27-32 ° C, and night temperature of about 26-27 ° C. The temperature at the point of heating to 45 ° C must be maintained for at least 12 hours per day. To check the temperature using thermometers. Humidity should be moderate.
Extra light and heat are required for monitors of all ages. Lights should be on 12-14 hours a day. The temperature measured right under the basking site should be 88-92° F. For thermoregulation, part of the habitat should be 5-10°F cooler. As for most amphibious monitors, the Nile ’s activity temperature is relatively low, about 90° F. For juveniles, overhead spotlights are sufficient. For monitors over 30” in length, one needs combinations of large reptile heat pads and at least 2 spotlights, or 1 spotlight and 1 infrared ceramic incandescent heat bulb over one or more basking sites. These can be controlled by rheostats or thermostats. Monitors benefit from exposure to a UV-B source (e.g., ZooMed® 5.0 fluorescent bulbs) when young, and for larger animals, mercury vapor reptile UV-B bulbs. Alternatively, an area can be provided where Nile monitors can bask in unfiltered sunlight (through a welded wire screen-covered window or in an outdoor plastic-coated welded wire cage during the summer).
Cleanliness
Nile monitors tend to excrete in the water dish. So, you need to clean the dish every day or whenever it's soiled. Also, make sure that the water tub is big enough that they can soak in it fully.
Health
Nile monitors can develop metabolic bone disease if they lack UV light or calcium in their diet. They can also catch infections caused by the Dracunculus sp. larvae. They often suffer from constipation as they usually eat a lot and many different things - some of which they may not be able to digest. Since you may find it hard to detect some of these conditions in your monitor, you should regularly get them checked by a vet who specializes in lizards. Wild-caught animals should be checked for internal parasites.
Temperament and Taming
Nile monitor lizard has a very aggressive nature, and has a strong bite its tail, so it is very dangerous. With regular communication with a host of positive Nile monitor lizard can be somewhat tamed. Females raised since hatching may be tame when kept in larger front-opening cages. They are generally less active than males.