The correct diet for a lizard depends on its species and age. People can feed most young lizards insects such as crickets, beetle larvae, flies and moths. Adult lizards exhibit greater variation in their diet, as some are strict herbivores, others prefer live prey and still others are eager to eat both.
Most small species, including geckos, anoles and chameleons, are completely insectivorous, although a few geckos lap baby food or soft fruit. Most midsized lizards, such as bearded dragons, blue tongue skinks and spiny-tailed iguanas, are omniovorous. Feed such species a variety of foods, including leafy green vegetables, low-sugar fruits, insects and rodents. The two primary types of large lizards — the iguanas and the monitor lizards — have very different dietary preferences. Iguanas are primarily herbivorous and should be fed an assortment of fruits and vegetables. In contrast, monitor lizards are exclusively carnivorous; feed them a variety of insects, rodents and birds. Additionally, some aquatic species may appreciate fish on occasion.
Be aware that prey items can and do fight back against their predators. Accordingly, it is safest to offer prekilled prey items to lizards that require rodents or birds. Most pet stores that sell lizards offer frozen rodents, which can be purchased in bulk and thawed and offered to the lizard as necessary.