Great care should be taken when deciding what substrate your lizards will live on. Unsuitable substrates may make it difficult for the lizards to walk nonnally and can cause irritations of the skin, particularly under the feet. Because almost all species love to dig they should be provided with at least some areas of soft substrate. The main disadvantage of soft substrates is that they are more difficult to keep clean than floorings such as tiles and newspaper, which can simply be lifted out and scrubbed or replaced. However their advantages to the lizards' well-being make it well worthwhile taking extra trouble to remove all traces of fecal material as soon as they appear. Some keepers object to soft substrates on the grounds that the lizards tend to swallow particles along with their food. In the wild monitor lizards almost always have bits of debris in their stomachs including sand, gravel, soil and bits of wood. It appears to pass through them without causing any mishap, but because ingestion of large amounts of some substrates can be injurious, sharp sands and gravels should be excluded from the terrarium.

The choice of substrate depends on the natural habitat of the species concerned. For desert species sand is the obvious choice. The type used should be fine and free from sharp edges. Builders' sand is not suitable and neither are most gravels. Sand can be dug up or bought from a garden centre. If collected in seashore areas it should be rinsed free from salt. For most other species a substrate of a mixture of sand and leaf mould or bark chippings is ideal. Avoid peat and other dusty substrates that become airborne when dry because they tend to cause respiratory problems. There are various artificial substrates available which are made especially for terrariums, but they are very expensive in the quantities nonnally required for monitors. Eidenmuller (1986) suggests that cat litter makes an ideal substrate for some smaller species. Regardless of the substrate used it need be no more than 15-30cm deep if artificial burrows are provided. Large volumes of substrate are unstable unless held together by plant roots so big monitors are best prevented from digging deep burrows in order to eliminate the dangers of them collapsing and burying the lizards alive. Generally monitors prefer to steal burrows of other animals rather than go to the trouble of digging them.

The type of substrate used and its ability to retain moisture will have an important effect on the humidity of the enclosure. For species that like high humidity the substrate can be kept damp and the rate of evaporation increased by gently heating the substrate with a mat or a cable. Even for desert species it is a good idea to spray the sand with a little water several times each week, so that the lower layers are always slightly damp.

In temporary quarters (such as quarantine) newspaper or corrugated cardboard make the best substrate as they can be replaced every day. They are unsuitable for everyday use because they do not afford the lizards a good grip, and are soon ripped to shreds by energetic digging behaviour. Cork tiles can also be used. They have the advantage of affording the lizards good grip whilst still being easy to clean and replace. Paving stones make an excellent substrate for rock dwelling monitors.

Gravity ensures that most of the bacteria in the enclosure live on the bottom and great care must be taken to ensure that all traces of faeces are removed from the terrarium as soon as they appear.

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