Varanus niloticus
(Nile monitor)

V. niloticus, the Nile monitor, is a large, mainly aquatic, lizard. It has been introduced to Spain (Pleguezuelos, 2004), and in the United States in Massachusetts (Cardoza et al., 1993) and Florida (Dalrymple, 1994; Duquesnel, 1996; Campbell, 2003, 2005; Enge et al., 2004). All known introductions are via the pet trade invasion pathway (Kraus, 2009; Krysko et al., 2011a).  This species is established (i.e. has reproducing populations) only in Florida, where it was first illegally introduced in ca. 1990 (Krysko et al., 2011a, b).

The distribution of V. niloticus in Florida covers hundreds of square kilometers and is expanding, especially along the enormous network of man-made canal and levee banks in southern Florida. The main ecological impacts are currently on native animals that may be consumed as prey, including rabbits (Sylvilagus sp.), burrowing owls (Athene cunicularia), waterfowl, American alligators (Alligator mississippiensis), American crocodiles (Crocodylus acutus), frogs, snakes, terrestrial and freshwater turtles, and sea turtles, many of which are protected species. Additionally, non-native species may be consumed such as goldfish (Carassius auratus), Cuban treefrogs (Osteopilus septentrionalis), Cuban brown anoles (Anolis sagrei), and domestic animals such as poultry (Bennett, 1995; Cowles, 1930), cats (McGraw, 1992; Bennett, 1995), and dogs (Enge et al., 2004). V. niloticus may pose a threat to human health, especially when cornered or captured because it will vigorously defend itself by biting, clawing, or tail whipping (Cowles, 1930; Branch, 1998; Faust, 2001; Enge et al., 2004).

 In Florida, V. niloticus is considered a pest species and is currently listed as a ‘conditional species’ by the Florida Fish and Wildlife Conservation Commission. Although conditional species are not allowed to be acquired for personal possession, reptile dealers, researchers and public exhibitors may purchase an annual permit for its importation or possession. Residents who owned a V. niloticus before 1 July 2010 may keep the animal for the remainder of its life; however, pet owners must maintain a valid Reptile of Concern license. Outside of Florida, regulations on ownership and possession of V. niloticus are highly variable and ownership may possibly be prohibited altogether. Since 1975, this species has been listed as Appendix II of CITES, which allows monitoring of the pet trade and skin industry.

V. niloticus is native to sub-Saharan Africa excluding desert regions; it occurs along desert fringes, in grasslands, rainforests, rivers, swamps, ponds, lakes and seashores (Luxmoore et al., 1988, Faust, 2001, Bayless, 2002; Spawls et al., 2002). It is currently established in at least three of these areas of Florida (Cape Coral, West Palm Beach, and Homestead) where it is expanding its range (Enge et al., 2004; Krysko et al., 2001b).

V. niloticus inhabits human areas and cultivations, often foraging around rubbish dumps (Bennett, 1995; Faust, 2001) where it seeks refuge in crevices or burrows, including those made by other animals (Edroma and Ssali, 1983). This species is mainly aquatic. It may hide in dense vegetation in shallow water or use bare tree trunks, logs, rocks, or overhanging branches as basking sites (Edroma and Ssali, 1983; Lenz, 1995; Muhigwa, 1998; de Buffrénil and Hémery 2002; Spawls et al., 2002). When alarmed, it will quickly dive into the water and swim far away or remain submerged for more than 20 minutes (Cowles, 1930; Bennett, 1995; Branch, 1998; Spawls et al., 2002). In Florida, it is found in mangrove swamps, tidal creeks, edges of freshwater and saltwater marshes, and banks of rivers, canals and lakes (Enge et al., 2004).

Reproductive Biology

V. niloticus is a prolific species (Western, 1974). In its native range, females oviposit in burrows or termite mounds between August and January (Branch and Erasmus, 1982; Bennett, 1995; de Buffrénil and Rimblot-Baly, 1999; Spawls et al., 2002). In Mali and Chad, females reach sexual maturity at 24 months of age or ca. 36 cm snout-vent length (SVL), and ca. 50% of mature females reproduce each year (de Buffrénil and Rimblot-Baly, 1999). Smaller females usually oviposit 12–13 eggs (3 x 5 cm), but larger (>71.5 cm SVL) females may oviposit 53–60 eggs (de Buffrénil and Rimblot-Baly, 1999; Spawls et al., 2002). Eggs may take 6–12 months to hatch in the wild (Cowles, 1930; Faust, 2001; Spawls et al., 2002). Neonates have been observed in January in southern Kenya, and in July in northern Kenya and northern Tanzania (Spawls et al., 2002).

Little reproduction data has been documented in its invasive range in Florida. Enge et al. (2004) found eight well-developed eggs, possibly an incomplete clutch, inside a female (52 cm SVL), collected in Florida.

Longevity

V. niloticus can live for more than 10 years in the wild and 15 years in captivity (de Buffrénil and Hémery, 2002).

Activity Patterns

V. niloticus is mainly aquatic during activity periods, at times hiding in dense vegetation in shallow water (de Buffrénil and Hémery, 2002).

Population Size and Structure

V. niloticus can attain high population densities (Western, 1974). Despite V. niloticus having the widest distribution of any monitor lizard species in Africa (Bayless, 2002; Spawls et al., 2002), little is known regarding population structure in its native range and no study has addressed the origins of invasive populations in Florida.

Nutrition

V. niloticus is an opportunistic generalist predator in its native range that hunts or scavenges for arthropods, crabs, crayfishes, mussels, gastropods, fishes, anurans, lizards, turtles, snakes, young crocodiles, eggs, birds and small mammals, including domestic cats (Cowles, 1930; Cott, 1960; Cissé, 1972; Losos and Greene, 1988; McGraw, 1992; Lenz, 1995; Branch, 1998; Bennett, 2002). Nile monitors also feed readily upon human food scraps and carrion (Edroma and Ssali, 1983). Juveniles are typically better climbers than adults and prey primarily upon invertebrates (Bennett 1995, Lenz 1995, Faust 2001, Bennett 2002). Skull and tooth morphology changes with age (Rieppel and Labhardt 1979), allowing older monitors to crush molluscs and crustaceans, which are heavily preyed upon where available (Bennett 1995, Branch 1998).

Associations

Little is known of possible symbionts or similar floral/faunal associations.

Environmental Requirements

In its native range, V. niloticus is found in a vast array of habitat types, excluding deserts. These include along desert fringes, in grasslands, rainforests, rivers, swamps, ponds, lakes, and seashores (Luxmoore et al., 1988, Faust, 2001, Bayless, 2002; Spawls et al., 2002). In its introduced range in Florida, it is found in mangrove swamps, tidal creeks, edges of freshwater and saltwater marshes, and banks of rivers, canals, and lakes (Enge et al., 2004).

Notes on Natural Enemies

Predation on V. niloticus has not yet been documented in its invasive range of Florida. However, possible predators on small monitors include birds, snakes, American alligators (Alligator mississippiensis) and American crocodiles (Crocodylus acutus).

General

• Botanical garden/zoo
• Pet/aquarium trade
• Sociocultural value

Human food and beverage

• Meat/fat/offal/blood/bone (whole, cut, fresh, frozen, canned, cured, processed or smoked)

Materials

• Skins/leather/fur
• Tanstuffs

Until recently, two subspecies of V. niloticus were recognized: the Nile monitor, V. niloticus niloticus (Linnaeus, 1758), and the ornate Nile monitor, V. niloticus ornatus (Daudin, 1803). Based on morphology, Böhme and Ziegler (1997) elevated both to species status: V. niloticus and V. ornatus. V. Niloticus is diagnosed by having 6–11 (mean = 7) light-colored body bands and a bluish black tongue, and V. ornatus by having 3–6 (mean = 5) body bands and a pinkish tongue (Böhme and Ziegler 1997; Faust, 2001).

Due to the variable regulations around (de)registration of pesticides, your national list of registered pesticides or relevant authority should be consulted to determine which products are legally allowed for use in your country when considering chemical control. Pesticides should always be used in a lawful manner, consistent with the product's label.

SPS Measures

There does not appear to be quarantine or certification measures associated with importation of V. niloticus. In Florida, ownership is regulated by its listing as a 'conditional species' by the Florida Fish and Wildlife Conservation Commission. Outside of Florida, regulations on ownership and possession of V. niloticus are highly variable and it is possibly prohibited altogether. Since 1975, this species has been listed as Appendix II of CITES, which allows monitoring of the pet trade and skin industry.

Early Warning Systems

There is no dedicated early detection and rapid response system for V. niloticus in Florida. However, the Everglades Cooperative Invasive Species Management Area (CISMA) has been involved in the early detection and rapid response of the West Palm Beach population of V. niloticus, in southeast Florida.

Public Awareness

There have been no public awareness programs dedicated to V. niloticus in Florida. However, several Pet Amnesty Days are scheduled around the state each year where the public is allowed to surrender unwanted pets with no questions asked. There is also a hotline for pet owners to surrender them at any time in Florida.

Eradication

There is no dedicated eradication program for V. niloticus in Florida. Most individual animals are removed opportunistically by humans.

Control and Sanitary Measures

There are no known control methods or sanitary measures for V. niloticus in Florida.

Monitoring and Surveillance (incl. Remote Sensing)

There is no dedicated monitoring or surveillance for V. niloticus in Florida.

Although little is known about V. niloticus in its invasive range in Florida, studying these animals in the wild there should be secondary to dedicated eradication attempts. Nonetheless, in areas where eradication is unfeasible, studies should be conducted on gathering life history data to help manage this pest species, as well as determine the origin in its native distribution, via genetic testing, to create a thorough phylogeographic study.