My terrapin eats the gravel in his tank. Why is this, and does it matter?
Such behaviour usually starts as terrapins grow older, and similar behaviour has also been recorded in crocodiles, although the reasons for it are not clearly understood. It has been suggested that it could have some beneficial effect on the reptile's buoyancy.

Another thought is that the gravel might help them to digest their food, being rather similar to the way in which birds eat grit to help them grind up seeds. Eating gravel does appear to be more common in terrapins fed on a diet of meat and fish, rather than a specially-formulated complete food. This also raises the possibility that it could be triggered by a nutritional deficiency - perhaps a shortage of calcium. Terrapins kept on this type of diet are likely to be deficient in this vital mineral, if you are not using a supplement. Changing the diet is therefore be recommended. Prepared foods which offer a balanced diet are definitely to be recommended compared with meat or fish.

There is also the risk that if your terrapin eats a relatively large quantity of gravel, then this could cause an obstruction in its digestive tract, with serious if not fatal consequences. You could simply take the gravel out of the tank - it serves little purpose here, other than looking attractive, and it certainly makes the tank harder to clean properly.
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