When seen from above, a sexually mature female hamster has a trim tail line; a male's tail line bulges on both sides. One extinct hamster of Cricetus, for example, lived in North Africa during the Middle Miocene, but the only extant member of that genus is the European or common hamster of Eurasia. The best-known species of hamster is the golden or Syrian hamster ( Mesocricetus auratus), which is the type most commonly kept as pets. Hamsters are more crepuscular than nocturnal and, in the wild, remain underground during the day to avoid being caught by predators.

The coat of the winter white dwarf hamster ( Phodopus sungorus) turns almost white during winter (when the hours of daylight decrease). However, the differences in behavioral, chronobiological, morphometrical, hematological, and biochemical parameters are relatively small and fall into the expected range of interstrain variations in other laboratory animals. The entire laboratory and pet populations of Syrian hamsters appear to be descendants of a single brother–sister pairing. The Roborovski hamster ( Phodopus roborovskii) is extremely small and fast, making it difficult to keep as a pet.The best-known species of hamster is the golden or Syrian hamster ( Mesocricetus auratus), which is the type most commonly kept as a pet. They have thick, silky fur, which can be long or short, colored black, grey, honey, white, brown, yellow, red, or a mix, depending on the species. The average litter size for Syrian hamsters is about seven pups, but can be as great as 24, which is the maximum number of pups that can be contained in the uterus. Molecular phylogeny of the Cricetinae subfamily based on the mitochondrial cytochrome b and 12S rRNA genes and the nuclear vWF gene" (PDF).

conducted a molecular phylogenetic analysis of 12 of the above 17 species using DNA sequence from three genes: 12S rRNA, cytochrome b, and von Willebrand factor.

This kind of thermoregulation diminishes the metabolic rate to about 5% and helps the animal to considerably reduce the need for food during the winter.

The hamster tail can be difficult to see, as it is usually not very long (about 1⁄ 6 the length of the body), with the exception of the Chinese hamster, which has a tail the same length as the body.Wild hamsters will also appropriate tunnels made by other mammals; the Djungarian hamster, for instance, uses paths and burrows of the pika. Mother hamsters can also use their sense of smell to find their own babies and identify which ones are not theirs.