Calcium supplementation is one of the most important aspects of captive reptile nutrition. Without adequate calcium and the vitamin D3 needed to absorb it, reptiles develop metabolic bone disease (MBD), a painful and potentially fatal condition that causes soft bones, tremors, and deformities.

The standard method is dusting feeder insects with a calcium powder immediately before offering them. Lightly coat the insects by placing them in a bag or cup with a small amount of powder and gently shaking. The goal is a thin, even coating rather than a heavy clump that the reptile might reject.

For reptiles with access to quality UVB lighting, use plain calcium carbonate powder without added D3 for most feedings. UVB exposure allows the animal to synthesize its own vitamin D3 in the skin, making dietary D3 less critical. Offer calcium with D3 once a week as a safety net.

For reptiles kept without UVB, such as some nocturnal gecko species, calcium with D3 becomes the primary supplement at most feedings, since the animal cannot produce D3 on its own. However, providing at least low-level UVB is increasingly recommended by veterinary herpetologists for all species.

A separate multivitamin containing vitamin A (preformed retinol for species that need it) and other trace minerals should be dusted once every one to two weeks. Over-supplementing fat-soluble vitamins like A and D3 can cause toxicity, so follow the product directions and veterinary guidance.

Leaving a small dish of plain calcium powder in the enclosure allows many species, particularly leopard geckos and bearded dragons, to lick it as needed. This self-service approach complements but does not replace regular dusting.

For herbivorous reptiles like iguanas and tortoises, calcium comes primarily from high-calcium greens like collard greens, mustard greens, and dandelion leaves. Occasional light dusting of salads with calcium powder provides additional support.