In tortoise-keeping circles, pyramiding is the single biggest fear. It is almost certainly the most common disease affecting pet tortoises today. In case you don’t know what pyramiding is, this picture explains it better than a thousand words –
A tortoise’s shell should always be smooth and domed. The individual scutes (patches) should not stand out like this. A real hallmark of a good tortoise-keeper is their ability to prevent pyramiding from happening.
So what causes pyramiding? Well, in one sentence, pyramiding happens whenever weak bones are put under strain by outward growth. There are two preconditions for it: first, the bone must be weaker than usual, and second, the strain placed on the scutes must be greater than usual. Let’s look at the causes of each of these in more detail.
One thing I and other tortoise enthusiasts emphasise is that tortoises must, must, must be given adequate vitamin D and calcium. The tortoise has a higher bone mass:total body mass ratio than any other animal I can think of, so naturally it needs lots of calcium and vitamin D to sustain that bone mass.
When this is not provided, bones become weak. They lose their density and take on a spongy texture. (This is similar to rickets or osteoporosis in humans.) This sets the stage for pyramiding, but first the weakened bone in the scutes must be pushed outwards.
Tortoises grow their shells by depositing keratin on the scutes from the middle outwards. As layers of keratin are deposited on the shell, it grows incrementally bigger. The layer of keratin are just like the growth rings of a tree, and give a record of the tortoise’s growth in the past.
This outward movement naturally creates a force pressing the scute up and out, towards the ‘pyramid’ shape, but the shell should have enough flexibility to accommodate this force without warping. This brings us to the other cause of pyramiding: stiff, inflexible keratin.
Keratin becomes inflexible when it dries out. It’s as simple as that. If your tortoise’s shell is particularly dark and the layers of ketatin are densely packed, take a good hard look at the humidity levels in the enclosure. Low humidity is usually the cause of a dried-out shell. It goes without saying that all tortoises should have access to enough water to drink as well.
On the other hand, if the humidity levels are too high the keratin absorbs too much moisture and becomes too soft and flexible. So a variety of microclimates must be provided for. You should take humidity readings in the enclosure and make sure they mimic what would be found in that tortoise’s natural environment, and that they vary from one part of the enclosure to another. If you don’t have a hygrometer to measure humidity, get one. They’re a must for any tortoise-keeper.
Let’s get real practical. Here’s what you need to do to prevent pyramiding:
- Provide a source of ambient humidity, such as a USB humidfier or a heat lamp over moistened substrate
- Provide a variety of microclimates, like a rock for your tortoise to climb onto, a box for them to hide into, and substrate that they can burrow into
- Sprinkle calcium carbonate powder on their food once or twice a week and give them plenty of calcium-rich vegetables. Limit phosphorous-rich foods (including meat), as phosphorous blocks the absorption of calcium. See Practical Tortoise Care if you want to be sure which foods are best to prevent pyramiding.
- Let them bask in UV light as much as they want, so they can synthesize vitamin D. See out article on housing your tortoises for more information on lamps.