Humidity is one of the most important aspects of proper monitor lizard enclosure setup, the other two being temperature and size. Humidity on tropical Indonesian islands is uniform throughout the year and mostly fluctuates within 75 to 85% range. This is what we are going to reproduce in our enclosure. There are several setup factors, that contribute to stable humidity values and retention.
Enclosure design. Enclosure has to be designed with
keeping humidity(and temperature) inside. It doesn’t have to be air-tight,
but amount of permanent openings have to be close to zero. Mesh, mosquito net
and other breathable materials can not be used in any combination for walls,
doors, tops or bottoms of the enclosure. Every side of the enclosure has to
be built from solid and water-sealed material like wood, plywood, plexiglas
and combination of those, with plexiglas mostly used for doors and windows.
Few additional regulated vents can be put in strategic areas of your enclosure,
based on design and desired air flow.
Humidity will have to be measured and controlled with either weather station, hygrometers or thermostats with humidity probes. More details in "Enclosure" section.
V. melinus enjoying warm bath
Substrate layer. Very important component of humidity retention. Thick (1 ft and up) and properly moist (not damp) substrate layer will hold and slowly release humidity over prolonged period of time. Once in awhile will need to be remoistened, either manually or automatically. Another important function of thick substrate layer is promoting digging and burrowing activity and temperature retention: the larger the substrate volume - the longer it will hold necessary temperature, so can help in case of power outages. One of the best and economically effective substrate layers is organic topsoil premixed with sand 80 to 20 ratio.
Misting system.The best result in humidity control is achieved by systems that produce fine misty rain, as it both humidifies the air and moistens the substrate layer. These systems can be controlled via simple timer or more sophisticated devices with humidity probes. Use of ultrasonic foggers is not recommended, as those produce unnatural small particle cold fog, that may have negative effects on respiratory system of the animal and they don’t really moisten the substrate. One of the best and reliable complete misting solutions is Mistking. Similar to Mistking effect can be achieved with cheaper DIY solutions or manual misting.
Water feature in V. melinus enclosure
Water feature. Varanus melinus is an aquatic monitor lizard and requires a water feature to be fully submerged as a minimum and large swimming pond at best. Water promotes various aquatic activities, swimming, diving and underwater foraging. Also soaks the animal and helps with shedding. For best results water has to be heated to 80-84F range, as it is normal water temp in Indonesian mangrove swamps, river deltas and ocean. Can also be continuously filtered to prolong time between water changes. Heated and moving water supports humidity by evaporating faster. Secondary function is temperature retention, as large volume of water has large heating capacity and can also help in case of power outages.
Failure to provide necessary humidity levels will lead to various health complications. It will cause problems with shedding, down to the point when stuck unshed skin prevents blood flow and animal may lose toe, tail or limb. Also, since monitor lizards don’t have sweat glands and pores, dehydrated monitor would not be able to properly excrete toxic products of metabolism from it’s body and can develop gout and related health issues. Constipation and impaction are another dangerous health risks of improperly low humidity.