Introduction
The pet hobbyist has slightly different needs for their reptile bedding than do large breeders. However, both hobbyists and breeders have found that substrate materials used for reptiles all have good and bad points. Factors that each pet owner must consider include heat transmission, safety with regard to ingestion, ease of cleaning (or disposability), suitability for use with feeding insects, ability to remain in place (or the opposite, suitability for burrowing species), odour and/or dust accompanying, absorbency, appearance, and cost.

One of the most important factors is safety. Many pet reptiles become ill after intestinal obstructions develop from sand, gravel, bark, corncobs, shavings, or other beddings. Yet some of these substrates are very suitable for certain species when used correctly. The easiest and best way to select a bedding is to look at the requirements needed. Is the bedding for a very small juvenile? Will the bedding be used in conjunction with an undertank heater? What other types of heating devices might be involved? Does the animal eat insects that may tend to hide such as crickets? Will the animal have high humidity requirements, or must the substrate stay as dry as possible? Will a feeding platform be used or could food fall on the bedding and be eaten accidentally?

Although feeding platforms can reduce the risk of food being swallowed with bedding, there are other factors to consider. As some species explore a new environment, they check the fresh bedding with the tip of their tongues, a practice that could prove harmful if bedding sticks to the tongue and is inadvertantly swallowed. Purposeful ingestion of bedding is also possible. Some hobbyists have told me that iguanas like to eat gravel or "grit" to help grind or digest their food, in a manner similar to that of a bird. However, there is very little anatomical evidence to support this theory. Eating soil or stones in a search for trace minerals missing from the diet is also theoretically possible, but not yet documented in the reptile. Heat transmission is another important factor when selecting bedding.

This is particularly true for ground dwelling species. If these animals are maintained on substrates with insulating properties, such as shredded aspen, corncobs, or recycled paper pellets, then much of the heat from an undertank heater may fail to contact the animal well. Deep bedding may worsen the problem, but this is often recommended to prevent some reptiles from accidentally contacting the heater surface. Some beddings tend to stay in place better than others and so can be used in lesser amounts. And sometimes the overall enclosure temperature will be high enough to negate the effect of insulation. Beginning hobbyists must carefully watch the appetite and feeding behaviour of their new reptile. Insect eating species that dine on crickets cannot be monitored adequately (especially in those first few critical weeks) if the crickets secrete themselves under layers of newspaper, shavings or bark nuggets. It is always difficult to be sure if the crickets have actually been eaten or if they are hiding. For this reason, advanced planting or landscaping of the terrarium is usually best saved until after the reptile is well established and its feeding behaviour is set.

Moist and dirty conditions are an enticing invitation to deadly opportunistic bacteria such as Pseudomonas, Aeromonas, and many others. High humidity will benefit many tropical species, but the environment will have to be cleaned frequently if the multiplication of these bacteria is to be avoided. This cannot practically be done with substrates that are too difficult to clean, too heavy, or too costly. For this reason, disposable beddings are popular with many hobbyists. Other species need very clean and dry conditions to do well. Some of these species benefit from very absorbent beddings such as shredded aspen or recycled paper pellets. The above factors are summarised and contrasted for some of the most common or popular substrate materials listed below.

SOIL
(natural earth, not necessarily potting soil): Economical if collected yourself, but some hazards may be involved in doing this. Commercial potting soils are sterilised and so this may be preferable in some instances. However parasites (including mites) which may be contained in natural source substrates are rarely transmissible to pet species. Most species of parasite are very host specific and North American species would rarely affect tropical lizards or snakes. However, bacterial contamination may be a problem, and soil may cause humidity problems in the terrarium when heated. It should be changed frequently as it will support bacterial growth. Difficult to clean tank after use. May look pleasing initially. Transmits heat well. Crickets generally available on the surface of this substrate.

AQUARIUM PEBBLES
Large ones are safe and attractive. Commercial pebbles are recommended as they are already uniform in size. Not inexpensive, but can be cleaned and re-used if the pebbles are large enough (smaller gravel is almost impossible to clean and dry). Pet owners must have plenty of spare time for this. Use a "double set" of pebbles, one clean set ready to place in the terrarium, and one set in use. To clean a removed set, place in a large bucket and soak in water for at least one half hour. Stir and rinse until all visible soiling is removed and the water runs clean. Use a disinfectant solution as recommended by your veterinarian (usually soaked for at least one half hour again), then rinse very well. Dry on newspaper. Pebbles transmit heat well and natural colours usually look quite pleasing in the terrarium. Make sure they are too large to be accidentally ingested by the species being housed on them. Crickets can't normally hide under pebbles so this substrate is often used for small ground dwelling insect eaters.

AQUARIUM GRAVEL
Ingestion is often a problem, and cost can be a negative factor if disposed of each week. Unfortunately, gravel is more difficult to clean than pebbles. Large quantities of gravel are heavy to transport. Easily ingested by some species and may cause impactions. Gravel does transmit heat well and is aesthetically pleasing when natural colours used. Crickets can't hide in this type of bedding. Moisture and water may pool underneath unseen, harbouring bacteria.

SAND
moderate pricing, but heavy to transport and it can be difficult to clean the tank or terrarium properly. May possibly cause sand impactions if food falls on the sand, or if sand is accidentally eaten during cricket catches. Necessary for certain less common burrowing species. Transmits heat from bottom heaters very well. Looks good unless soiled. Suitable for many insect eaters as crickets are well exposed on this substrate.

PINE SHAVINGS
Generally only useful for very large specimens that hopefully will not accidentally ingest it (ie varanids and boids). More aromatic shavings such as cedar are not usually recommended. Pine shavings are inexpensive, absorbent, and may help minimize the growth of reptile pathogens such as Aeromonas and Pseudomonas if changed regularly. Crickets can hide in it so is rarely used with insect eaters. Pine shavings do not transmit heat well. They are easily moved aside so burns can also result if a very hot undertank heater is used. May not look natural. Related beddings such as hardwood chips (most are actually very tiny squares of oak) are more useful but more costly.

SHREDDED ASPEN
Higher in price than shavings but also safer and more popular with reptile professionals. As with all disposable beddings, cleaning the terrarium is simplified.. Very absorbent and helps minimize bacterial contamination. It eventually forms a dense mat and so is not easily moved off an undertank heater, but will also insulate it and not transmit heat well. As many professionals use heated rooms they are not too concerned about this. Hobbyists might find this suitable for use in conjunction with an overhead incandescent heat source. Dense enough so crickets can't usually hide in it. Looks somewhat natural.

CORN COBS
Not usually recommended for common species as they tend to swell and cause obstructions if swallowed. If the animal can be fed in a manner that will prevent ingestion, they have some benefits. Pelleted or ground corn cobs are extremely absorbent, they are disposable, crickets can't hide under them, and they almost always looks clean and neat. However they also insulate undertank heaters (do not transmit heat well). Once moist, they will support mold growth so must be changed regularly.

NEWSPAPER, BROWN or "BUTCHER" PAPER
Very inexpensive, clean/disposable, and inks (if present) are now generally non-toxic. However, reptiles and crickets can sometimes get under it. Does not usually make an attractive substrate, so is more popular with breeders than pet owners or people displaying their animals for public viewing.

BARK, CYPRESS MULCH
Large bark nuggets are often popular as a substrate for iguanas. When purchased in bulk, they are inexpensive and disposable, so hygiene is simplified. Feeding should still be done on a slate platform or other feeding platform as occasionally small chips are present and may be accidentally ingested. Cypress or other wood/bark mulches are also popular but again, ingestion should be prevented. There are no published reports of any parasite transmission associated with non sterile bark products (see previous comments regarding "soil"). Good quality bark always looks very attractive in the terrarium. Large nuggets are not really suitable for insect eaters as the crickets will hide amongst the bark. Small chips will prevent this but make sure they are not being eaten along with the crickets. Will not transmit heat well from an undertank heater, but cannot easily be pushed aside.

PLASTIC "GRASS" OR CARPETING
Difficult to clean quickly so use a double set. Careful attention must be paid to the complete cleaning and disinfection of this substrate each week. May look artificial. However it cannot be ingested and transmits heat reasonably well. Some reptiles or crickets may try to get underneath which is undesirable. Fraying of the edges has also been associated with intestinal obstructions so watch the condition of this material carefully.

RECYCLED NEWSPAPER LITTER
This is more or less safe if ingested in small quantities (safer than corn cobs or shavings), some types look a little bit like grey gravel, and it is compact enough to transmit some heat and stay in place quite well. It is a disposable litter so simplifies hygiene and crickets cannot hide beneath it. It is extremely absorbent and will not support mold or bacterial growth. Many miscellaneous types of bedding are also now in use; everything from "grass" pellets, rabbit pellets, corn by-product pellets, and dried citrus by-products to ground walnut shells. Rabbit pellets seem an unlikely choice for bedding, but if they are accidentally ingested, they will not obstruct the animal - usually iguanas - and they are a reasonable source of nutrition. This is because they are based on alfalfa and so have good calcium and fiber levels. However, some of these pellets may have unacceptable protein and carbohydrate levels, so cannot be recommended as an ongoing source of nutrition. Many of the other new beddings are good choices. However, don't forget to consider factors such as ingestion problems before selecting any new bedding. Check with your reptile veterinarian if you have concerns about the safety of a new bedding with your own pet. If you have had any positive or negative experiences with any of the beddings or substrates described, please share your comments with us. Remember that each reptile individual may behave differently - expect the unexpected!