Mertens' monitors are a medium to large-sized monitor species with a typical snout-vent length (excluding the tail) ranging from around 30-45cm in adults.

The coloration of Mertens' monitors is predominantly olive grey to brown over the body, with scattered cream or yellow spots. Adult males tend to exhibit a stronger colored pattern. The underside of the monitor is light cream in color, and they have a yellowish throat. They possess the typical physical features of water monitors, including a laterally flattened tail, but this characteristic is more pronounced in Mertens' monitors. Their nostrils are located on the upper side of the snout.

​

Mertens' monitors are a semi-arboreal and semi-aquatic species found in rivers, watercourses, and lagoons across the far north of Australia.

Once settled in, Mertens' monitors become well habituated to human interaction and presence. Tong feeding can be easily established, and they are known to exhibit higher intelligence compared to many other monitor species. Interaction with Mertens' monitors is rewarding, and they are considered a highly desirable species to keep.

​

Husbandry for Mertens' monitors is relatively easy, with the exception of requiring more enclosure space due to their larger size. They thrive in outdoor enclosures year-round in Far North Queensland (FNQ). In southern states, caution is needed during the cooler months, particularly to ensure that water sources are kept warm enough. Keeping them indoors requires a large enough water source for them to submerge, considering that they can make quite a mess.

​

Mertens' monitors are known to utilize their water source extensively compared to other water monitors in Australia. They spend a significant amount of time in the water foraging and soaking.

​

Enclosure size: Given their semi-arboreal and semi-aquatic nature, both vertical and horizontal space should be provided. Large enclosures or pits can be used indoors or outdoors, taking into account the heating requirements. Enclosures for adults should be around 2m x 2m, but larger enclosures are preferable.

​

Substrate and furnishings: Sand, soil, or large pebbles can be suitable substrates. Large pebbles are preferred for water species to prevent them from sticking to the wet body and being dragged into the water source, which can lead to faster fouling. Plenty of hollows, hides, and climbing branches are needed for their enrichment.

​

Temperatures and lighting: Adequate UVB lighting is essential for internal keeping. A basking hot spot with a bright lamp directed onto a rock or tiles should be provided, with temperatures ideally ranging from 50-65°C. The ambient heat gradient over the rest of the enclosure should be around 28-33°C during the warmer active months.

​

Humidity: Mertens' monitors are from the tropical north, so it's important to maintain humidity levels for this species. Frequent misting and a constant water source are required.

​

Feeding: The bulk of their diet should consist of crickets, wood roaches, and other insects, with regular dusting of calcium powder and vitamins for young animals. Adults will consume whole prey such as fish, yabbies, prawns, rats, mice, quail, and other meats. It's important to maintain a well-balanced variety of food, considering the fat content. Note that a diet predominantly composed of frozen fish can lead to thiamine deficiency.

​

Life span: Mertens' monitors have an average recorded captive lifespan of over 17 years.