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:
- 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.
- 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
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