While most lizards are diurnal -- meaning they are active during the day and inactive at night -- a handful of species are nocturnal creatures who become active only after the sun sets. Most geckos are active at night, although a few clades have become diurnal over evolutionary time. A few other lineages include nocturnal members among their ranks as well.
Most ground-dwelling geckos, including leopard geckos (Eublepharis macularius), fat-tailed geckos (Hemitheconyx caudicinctus) and Madagascan ground geckos (Paroedura pictus), hide during the day and emerge at night. While many species engage in this strategy to avoid predators or to have easy access to insect prey, those living in desert environments may do so in part to avoid excessively hot daytime temperatures. Most such species consume insects and other invertebrates, although large individuals may consume small vertebrates.
While geckos of the genus Phelsuma are diurnally active, most other arboreal geckos are nocturnal. This pattern is consistent among most size classes, including small species, such as house geckos (Hemidactylus spp.) and satanic leaf-tailed geckos (Uroplatus phantasticus), as well as large species, such as tokay geckos (Gekko gecko) and crested geckos (Rhacodactylus spp.). In fact, scientists continue to discover and describe new nocturnal gecko species. Most of these species consume insects and other invertebrates, but some also add nectar and fruit to their diet.
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Aside from a few scattered observations of nocturnal foraging, monitor lizards are primarily diurnal. One exception is the twilight goanna (Varanus glebopalma), which is often observed remaining active after dark. Otherwise, twilight goannas are largely similar to other medium-size monitors. They primarily consume insects and small lizards, although they occasionally prey upon rodents or snakes. Occasionally kept as pets in their native Australia, these lizards are rarely seen in North American collections.
A Crepuscular Lizard
While nocturnality is the ancestral condition for geckos, and daytime waking is the normal state for most other lizards, the monkey-tailed skink is crepuscular -- its waking hours are dawn and dusk. The largest skink in the world, the monkey-tailed has good eyesight, which helps the lizard find food in low light. The monkey-tailed is also called the Solomon Island skink and various other names.