A variety of common pets are nocturnal, meaning they spend their days sleeping, and only become active as the sun starts to set. Different species become nocturnal for different reasons; some may need to avoid diurnal, or day-active, predators, while others sleep away the day to avoid the harsh sun. Predatory pets, such as snakes and some lizards, often become active at night because that is when their prey is active.
Understand that some animals that are nocturnal in the wild shift to a diurnal activity pattern in captivity. Additionally, even strongly nocturnal species may become active during the day from time to time -- pets are active as their needs dictate, not according to the labels humans use to describe them.
The ancestors of many common mammalian pets -- including some of the most familiar, such as cats -- are typically nocturnal in the wild. However, cats (Felis catus) and many other animals who have undergone the process of domestication, become flexible in their habits, and may be active during the day as at night. Dogs (Canis lupus familiaris), for example, are largely active when their owners are, yet their evolutionary ancestors -- wolves (Canis lupus) -- are largely nocturnal. Ferrets (Mustela putorius furo) also exhibit this phenomenon, as they may be active at any time of the day or night, while their presumed forbearers -- European polecats (Mustela putorius) and Steppe polecats (Mustela eversmanii) -- are typically nocturnal. Domestic rabbits (Oryctolagus cuniculus) are similarly flexible, despite having nocturnal ancestors.
Other nocturnal mammalian pets include chinchillas (Chinchilla brevicaudasa) and many rodents, such as rats, mice and hamsters. However, gerbils and guinea pigs are often active intermittently throughout the day and night.
Many snakes sleep away the day and become active at night, although some species shift their activity patterns to adapt to changing temperatures. For example, many North American snakes, such as kingsnakes (Lampropeltis spp.), rat snakes (Pantherophis spp.) and water snakes (Nerodia spp.) are diurnal when temperatures are relatively cool and nocturnal when temperatures climb. Other nocturnal snakes include most pythons, such as ball pythons (Python regius), green tree pythons (Morelia viridis) and carpet pythons (Morelia spilota ssp.), as well as boas and their kin, such as boa constrictors (Boa constrictor ssp.), sand boas (Eryx spp.) and anacondas (Eunectes spp.). Most milksnakes (Lampropeltis triangulum ssp.), gray-banded kingsnakes (Lampropeltis alterna) and glossy snakes (Arizona elegans) are strongly nocturnal.
Generally, most lizards are diurnal, but a few exceptions exist. Aside from the diurnally active day geckos (Phelsuma spp.), most geckos -- including leopard geckos (Eublepharis macularius), fat-tailed geckos (Hemitheconyx caudicinctus) and crested geckos (Rhacodactylus ciliatus) -- are nocturnal. Most skinks are sun-loving species, but the prehensile-tailed skink (Corucia zebrata) is almost exclusively nocturnal.
Nocturnal behaviors are not limited to terrestrial reptiles. Most crocodilians exhibit increased activity after dark, including common pet species, such as spectacled caiman (Caiman crocodilus). Several aquatic turtles -- particularly snapping turtles (Chelydra serpentina), stinkpots (Sternotherus odoratus) and their relatives -- are most active at night.
The majority of the world’s amphibians are nocturnal. Part of this trend occurs because the permeable skin of amphibians causes them to desiccate rapidly in hot, dry weather. Accordingly, they tend to remain hidden in damp, cool retreats while the sun is high, and move about at night, when temperatures are cooler and the relative humidity level is higher. Exceptions to this rule are usually native to damp rain forest habitats, such as the poison dart frogs (Dendrobates spp.), who are nocturnal.
Most tree frogs, including green tree frogs (Hyla cinerea), red-eyed tree frogs (Agalychnis callidryas) and White’s tree frogs (Litoria caerulea) are nocturnal. Likewise, most commonly kept salamanders, such as tiger salamanders (Ambystoma tigrinum), are active at night.
While their nocturnal activities often escape notice by their keepers, many common pet fish species become more active at night than during the day. For example, fire eels (Mastacembelus erythrotaenia), fossil catfish (Heteropneustes fossilis) and snowflake moray eels (Echidna nebulosa), are nocturnal species. Additionally, many commonly kept sharks, such as epaulette sharks (Hemiscyllium ocellatum), are primarily nocturnal.
Many common invertebrate pets are nocturnal creatures; most tarantulas, for example, are nocturnal. This includes both arboreal species, such as pink-toed tarantulas (Avicularia avicularia), as well as terrestrial species, such as Mexican red-kneed tarantulas (Brachypelma smithi). Additionally, Madagascan hissing cockroaches (Gromphadorhina portentosa), emperor scorpions (Pandinus imperator) and Amazonian giant centipedes (Scolopendra gigantean) are nocturnal.