The feeding patterns of lizards are extremely diverse. Lizards may be insectivorous (eg, day and leopard gecko, whiptail lizard, anole, chameleon), carnivorous (eg, varanids such as monitor lizard, Gila monster, Mexican beaded lizard), omnivorous (eg, many iguanid and agamid species), or herbivorous (eg, iguanid species, prehensile-tailed skink).
Insectivorous lizards in captivity are usually fed diets of mealworm larvae or crickets. Because calcium concentrations in these, and in most insects, are extremely low (0.03%–0.3% calcium with 0.8%–0.9% phosphorus), the inverse calcium:phosphorus ratio must be corrected before the insects are fed to lizards. A diet with a balanced vitamin and mineral mixture and containing 12% calcium as calcium carbonate can be fed to crickets or mealworm larvae 3 days before the insect is fed to the lizard. However, this diet should not be used to maintain a cricket colony. Within 2 days of feeding the high-calcium diet, the gut of the insect is filled with calcium, raising the calcium concentration of the insect to ~0.8%–0.9% and resulting in a calcium:phosphorus ratio of ~1.2:1. A satisfactory high-calcium diet for crickets can be inexpensively made by using 29% wheat middlings, 10% corn meal, 40% ground dry cat or dog food, and 21% ground oyster shell or calcium carbonate (also see Nutrition in Bats for mealworm diet). Larger insectivorous lizards may also consume mouse pups and earthworms.
Carnivorous lizards may be offered mouse or rat pups, adult mice and rats, chickens, and eggs. The size of prey should be appropriate for the lizard species. Omnivorous lizards are usually fed a combination of foods, including insects, vertebrate prey, and a chopped vegetable mixture (see Nutrition in Tortoises for vegetable mix). Most lizards should be fed daily (juveniles and small species) or at least every other day. Large carnivorous species should be fed once or twice a week.
Herbivorous lizards are adapted to ferment plant fiber in enlarged hindguts. The microbes in the cecum and colon digest plant fiber that the lizard could not otherwise use. As with tortoises, herbivorous lizards should be fed plant-based diets to assure healthy gut function. The use of insects, vertebrate prey, or diets high in fruits is not advised, because these feeds are low in fiber and are inappropriate for herbivores. Diets for lizards may be commercial preparations formulated for herbivorous reptiles, or vegetable mixes (see Nutrition in Tortoises).