The Problem Of Space

A myth, that is extraordinarily common considering its stupidity, is that an animal "will grow to the size of its surroundings, and then stop"! This, of course, is utter nonsense. A healthy reptile never stops growing, from the day it is laid to the day it dies. Many monitor lizards spend most of the day fast asleep, and may not initially appear to very active animals. However when they do move they tend to cover a lot of distance. Typical daily forays for even dwarf monitors may be in excess of 200m per day and many monitors typically walk several kilometres in an afternoon. Obviously it is not possible to provide this amount of space for captives and it has been demonstrated that many species will do well in remarkably small enclosures. The term "small" is relative however. Captive lizards become lethargic in cramped surroundings for several reasons:

1. Thermoregulatory behaviour. Normal lizard behaviour involves movement from areas of one temperature to a warmer or cooler environment in order to maintain a preferred body temperature. In small enclosures the temperature is uniform and the lizards cannot alter their body temperatures significantly by moving. A large enclosure, on the other hand, may contain a range of temperatures, from 18-44°C for example. This gives the lizards the opportunity to select a body temperature that suits them and alter it at will. A small enclosure heated to 44°C would kill the inhabitants very rapidly.
2. Foraging. Monitor lizards do not swallow huge meals and then go to sleep for six months. They spend most of their active time searching for food; in leaf litter, under cow dung, underwater, on the branches of trees, in burrows, termite mounds, rock crevices, abandoned buildings etc., usually finding only small invertebrates. They also learn very quickly and a monitor kept in a small space quickly realises that there is nothing worth foraging for and stops looking. Larger, well-planned endosures may always contain concealed food items and promote more normal activity patterns.

Prospective purchasers of a baby water monitor usually fail to comprehend that the little brightly-colored lizard in the pet shop will soon grow into a formidable carnivore somewhere between two and three metres long and quite capable of putting its owner into hospital should it feel thus inclined. There is no reason why these animals should not be kept safely and successfully if their basic needs are met, and space is of primary imponance. Large terrariums are inconvenient because of the space they take up and can be expensive to keep warm. Nevertheless with careful planning they can be made unobtrusive and costs can be minimised. I have cited the smallest known enclosure in which the animals are known to have reproduced. A few of them are impossibly big and relate to animals kept outside in the tropics but most are a reasonable size.

A general rule for the larger species (i.e. those not belonging to the subgenus Odatria) is that the enclosure should be at least three times as long and twice as wide as the total length of the lizard at maximum size, measured from the tip of the tail to the tip of the snout. This allows them at least moderate space in which to move. An adult trio can be housed in enclosures of these sizes so long as ample basking and hiding places are provided. Arboreal species also need to be provided with a tall enclosure that allows them to climb at least their own body length above the ground. Monitor lizards grow so quickly that it is usually not sensible to have to build successively bigger enclosures as they increase in size. Dwarf monitors appear to need much less space than their larger counterparts. Many will live long lives in areas of less than 1m² if adequate furnishings are provided.

If space really is a problem, and the unfonunate creature is already in your possession, then it is better to try to tame the animal and give it the run of the house rather than keep it in a cramped terrarium. As long as they are provided with a suitable source of heat they should regulate their behaviour around keeping warm. Some monitors continually seek out the coldest pans of a room and lie there immobile for days or weeks. I presume that this is related to the need for an annual period of inactivity. Often they will conceal themselves somewhere that makes them very difficult to retrieve. It would be very foolish to allow a large untamed monitor lizard to wander about the house. Even tame ones will destroy your furniture.

Attribution / Courtesy: Daniel Bennett. 1995. A Little Book of Monitor Lizards. Viper Press U.K.