Cosy Tortoises Large cuttlefish bones are ideal for tortoises. A good source of Calcium easily accessed by tortoises, allowing them to have extra when they need it. Particularly, useful for egg-laying but all tortoises can replace most of their shell over 2 years and are continually replenishing it.  A good source of UVB light is essential for producing vitamin D in reptile skin.  Vitamin D is required to absorb Calcium.