Hamsters are rodents (order Rodentia) belonging to the subfamily Cricetinae, which contains 19 species classified in seven genera.

Hamsters feed primarily on seeds, fruits, vegetation, and occasionally burrowing insects.

In captivity, however, they are known to live a conventionally nocturnal lifestyle, waking around sundown to feed and exercise.[4].

Physically, they are stout-bodied with distinguishing features that include elongated cheek pouches extending to their shoulders, which they use to carry food back to their burrows, as well as a short tail and fur-covered feet.

Neumann et al. (2006) 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.

The results of another study[6] suggest Urocricetus kamensis and the related U. alticola belong to either this Phodopus group or hold a similar basal position.

[3] The entire laboratory and pet populations of Syrian hamsters appear to be descendants of a single brother–sister pairing.

These littermates were captured and imported in 1930 from Aleppo in Syria by Israel Aharoni, a zoologist of the University of Jerusalem.

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.

It is possibly related to Old Church Slavonic khomestoru, which is either a blend of the root of Russian хомяк (khomyak) "hamster" and a Baltic word (cf.

[13] Hamsters are typically stout-bodied, with tails shorter than body length, and have small, furry ears, short, stocky legs, and wide feet.

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.

[14][15] Their eyesight leads to them not having a good sense of distance or knowing where they are, but that does not stop them from climbing in (and sometimes out of) their cages or from being adventurous.

They tend to learn similar noises and begin to know the sound of their food and even their owner's voice.

[20] Hamsters are hindgut fermenters and often eat their own feces (coprophagy) to recover nutrients digested in the hind-gut, but not absorbed.

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.

[22] All hamsters are excellent diggers, constructing burrows with one or more entrances, with galleries connected to chambers for nesting, food storage, and other activities.

In the wild, the burrow buffers extreme ambient temperatures, offers relatively stable climatic conditions, and protects against predators.

[23] A burrow includes a steep entrance pipe (4–5 cm (1.6–2.0 in) in diameter), a nesting and a hoarding chamber and a blind-ending branch for urination.

Laboratory hamsters have not lost their ability to dig burrows; in fact, they will do this with great vigor and skill if they are provided with the appropriate substrate.

The female's reproductive life lasts about 18 months, but male hamsters remain fertile much longer.

Females are in estrus about every four days, which is indicated by a reddening of genital areas, a musky smell, and a hissing, squeaking vocalisation she will emit if she believes a male is nearby.

The breeding season is from April to October in the Northern Hemisphere, with two to five litters of one to 13 young being born after a gestation period of 16 to 23 days.

Female hamsters are also particularly sensitive to disturbances while giving birth, and may even eat their own young if they think they are in danger, although sometimes they are just carrying the pups in their cheek pouches.

British zoologist Leonard Goodwin claimed most hamsters kept in the United Kingdom were descended from the colony he introduced for medical research purposes during the Second World War.

[3] The Roborovski hamster (Phodopus roborovskii) is extremely small and fast, making it difficult to keep as a pet.

[28] When the first reported case of animal-to-human transmission of SARS-CoV-2 in Hong Kong took place via imported pet hamsters, researchers expressed difficulty in identifying some of the viral mutations within a global genomic data bank, leading city authorities to announce a mass cull of all hamsters purchased after December 22, 2021, which would affect roughly 2,000 animals.

Some activists attempted to intercept owners who were on their way to turn in pet hamsters and encourage them to choose adoption instead, which the government subsequently warned would be subject to police action.