Family Cricetidae
New World rats and mice, voles, hamsters, and relatives

Cricetidae is an extremely diverse family of muroid rodents. This is one of the largest families of mammals, with 681 species in 130 genera and 6 subfamilies. The subfamilies of Cricetidae are: Arvicolinae (lemmings, voles, and muskrat), Cricetinae (hamsters), Lophiomyinae (crested rat), Neotominae (North American rats and mice), Sigmodontinae (New World rats and mice), and Tylomyinae (vesper rats and climbing rats). (Musser and Carleton, 2005)

Cricetids range throughout North America, South America, Europe, and most of Asia from southern China northwards. (Nowak, 1999)

Cricetids occupy a broad spectrum of habitats. Their range encompasses dry, wet, warm and cold climates. Habitats utilized by cricetids include grasslands, meadows, agricultural fields, forests, rocky mountain landscapes, deserts, suburban yards, human habitations, beaches, lakes, ponds, streams, marshes, swamps, and bogs. They also span a range of elevations from sea level to over 5000 meters above sea level. (Nowak, 1999)

The taxonomic history of the family Cricetidae has been dominated by two main themes: either Cricetidae has been given full family status within the Muroidea (Tullberg 1899; Miller and Gidley 1918; Simpson 1945; Chaline et al. 1977) or the cricetid subfamilies have been largely placed within the family Muridae (Alston et al. 1876; Thomas 1896; Ellerman 1940, 1941; Musser and Carleton 1993). Those authorities who followed the former scheme have had different ideas about what belongs in the family Cricetidae. Tullberg (1899) excluded arvicolines, lophiomyines, and sigmodontines, to which he gave full family status. In their classification, Miller and Gidley (1918) placed the Nesomyinae and Gerbillinae within the family Cricetidae, as did Simpson (1945), who also included the Myospalacinae. Chaline et al. (1977) included the subfamilies Spalacinae, Myospalacinae, and Platacanthomyidae in the family Cricetidae. In recent years, analysis of large molecular datasets have helped to better understand the evolutionary relationships of these groups. Arvicolinae, Cricetinae, Neotominae, Sigmodontinae, and Tylomyinae form a clade sister to the family Muridae and distinct from all other Muroid groups. The sixth putative cricetid subfamily, Lophiomyinae, has not been included in most recent molecular analyses so its affinities remain uncertain. (Michaux et al. 2001; Jansa and Weksler 2004; Steppan et al. 2004). This distinct arvicoline/cricetine/neotomine/sigmodontine/tylomyine clade was recently recognized as the family Cricetidae (Steppan et al. 2004; Musser and Carleton 2005). Steppan et al. (2004) date the divergence between the family Cricetidae and its sister taxon, the family Muridae, at about 24 million years ago. (Alston, 1876; Chaline, Mein, and Petter, 1977; Ellerman, 1940; Ellerman, 1941; Jansa and Weksler, 2004; Michaux, Reyes, and Catzeflis, 2001; Miller and Gidley, 1918; Musser and Carleton, 1993; Musser and Carleton, 2005; Simpson, 1945; Steppan, Adkins, and Anderson, 2004; Thomas, 1896; Tullberg, 1899)

Many cricetids are mouse-like or rat-like in appearance: they have small, somewhat elongated bodies, and are gray or brown with long tails, large eyes, and prominent ears and whiskers. However, body forms in this diverse group vary. Arvicolines, cricetines, and some sigmodontines have rounded bodies, with short tails, small eyes, and ears that are almost completely hidden in the fur. Pelage colors in this family include nearly every shade of brown and gray, including light golden brown, dark russet, and black. There is a tendency for the undersides to be paler, and many species have white bellies and chins. Pelage color may vary within cricetid species, as well, with two or more color morphs found in some populations. The texture of the fur ranges from silky and soft to coarse and spiny. Tails may be tufted, well-furred, or nearly naked. Cricetids are small (pygmy mice of the genus Baiomys weigh up to 8 grams) to large (muskrats, Ondatra zibethicus, weigh almost 2 kg) relative to other rodents. Sexual dimorphism varies across species: in some cases, males are larger than females, and in other cases, females are larger than males. Some species do not exhibit sexual dimorphism at all. There are various specializations for different lifestyles found in this group; for example, the long, powerful claws of long-clawed mole mice (Geoxus) are adapted for digging, whereas the partially webbed hind feet and rudder-like tails of muskrats are adapted for swimming.

The cricetid dental formula is usually 1/1, 0/0, 0/0, 3/3 = 16. (Carleton and Musser, 1984; Nowak, 1999; Smith, Carmon, and Gentry, 1972)

As is the case with most small muroid rodents, cricetids face vast array of predators and usually live less than a year in the wild. Lifespan in captivity is often much longer, up to a decade in some species. (Nowak, 1999)

Cricetids are diverse in their behavior, as they are in all of their other characteristics. Some species are exclusively arboreal, while others rarely leave the ground, and some spend most of their time burrowing beneath it. Some are adapted for an aquatic lifestyle and are excellent swimmers. Most, but not all, cricetids are nocturnal. Cricetids often use torpor during cold periods to lower their energy requirements or aestivate when it is hot. Many build nests or burrows in which they seek refuge during periods of inactivity. Some species are known to be solitary and highly territorial, while others live in small social groups or in large colonies. Most are fairly sedentary, but some undergo huge population cycles and may disperse over large distances during periods of overabundance. (Nowak, 1999)

Cricetids use vision, hearing, touch, smell, and taste to perceive the world. The relative importance of these senses varies among species and relates to each species' lifestyle. For example, fossorial species tend to have a reduced need for vision, and often have reduced eyes, but may have a keen tactile sense. Some cricetids produce (and therefore are likely to hear) sounds that surpass the range of human hearing (Smith 1972). Chemical signaling with pheromones and scent marks is an extremely important aspect of communication in this group, as these odors can quickly send a signal about the identity and status of an individual (Johnston 2003). In general, cricetids communicate using a combination of chemical, tactile, visual, and auditory cues--the relative importance of which varies among species. (Johnston, 2003; Nowak, 1999; Smith, 1972)

Cricetids may be carnivores, omnivores, or herbivores. Food eaten by the group as a whole include leaves, pine needles, seeds, berries, fruits, roots, tubers, stems, twigs, nuts, fungi, insects, slugs, earthworms, aquatic crustaceans, spiders, small terrestrial vertebrates, and fish. Many cricetids are generalists that dine on many of these food items, while some are specialists that eat just one or two. Some cricetid species cache food for later use. (Nowak, 1999)

Cricetids are preyed upon by a variety of mammalian carnivores (such as foxes, cats, and weasels), birds of prey (such as hawks, eagles, and owls) and snakes.

In order to avoid easy detection by predators, many cricetids are nocturnal. Their neutral-colored coats tend to blend in with the surroundings and afford some degree of camouflage. When alarmed, they seek refuge in trees, burrows, or other places where the predator cannot follow. As a last resort, cricetids often bite their attacker with their sharp incisors and utter high-pitched chirps. One unique cricetid species, Lophiomys imhausi, bears aposematic white and black patches, exudes a musky odor, and has erectile, stiff hairs that may mimic porcupines. (Carleton and Musser, 1984; Nowak, 1999)

Cricetids are valuable members of many ecosystems, in which they fulfill roles as predators, prey, and dispersers of seeds and mycorrhizal fungi. Fossorial species turn over earth as they dig and therefore aerate the soil. Cricetids have a large impact on forest succession by preying on tree seedlings, and are sometimes considered keystone species when they play such roles (Manson et al. 2001). Their high reproductive output and regular boom and bust cycles in population numbers result in dramatic impacts on their plant prey species and predators that rely mainly on cricetid prey. Many types of parasites use cricetids as hosts, including species of ticks and mites, fleas, lice, bot flies, nematodes, and flukes (Kinsella 1991). (Kinsella, 1991; Manson, Ostfeld, and Canham, 2001; Nowak, 1999)

Some cricetids are vectors of human diseases, including hantavirus and lyme disease. Those that dwell in agricultural areas sometimes damage crops. Also, some species are considered nuisance animals when they enter homes, raid food stores, gnaw on household goods, and build nests in unwelcome places. (Nowak, 1999)

Some cricetid species, especially the hamsters, thrive in captivity and are popular pets. As research animals, cricetids have contributed greatly to the fields of ecology, physiology, and genetics. Some species are harvested for food or for their valuable fur. Also, cricetids play an important role in controlling populations of insect pests. (Nowak, 1999)

About 21% of the species in this family are included on the IUCN's Red List of Threatened Species. Of these, 58 are lower risk, 2 are near threatened, 27 are vulnerable, 27 are endangered, 11 are critically endangered, and 10 are lacking sufficient data. Another 6 (Pemberton's deer mice, Peromyscus pembertoni, Antillean giant rice rats, Megalomys desmarestii, Santa Lucia giant rice rats, Megalomys luciae, Darwin's Galapagos mice, Nesoryzomys darwini, indefatigable Galapagos mice, Nesoryzomys indefessus, and Nelson's rice rats, Oryzomys nelsoni) have gone extinct in recent years. Human-induced habitat loss and degradation threaten most of these species. Also, many cricetids have restricted geographic ranges, making them even more vulnerable to extinction. Few actions, other than basic research, are underway to conserve these and other rodent species, as most attention is directed toward saving larger, more charismatic fauna. (IUCN, 2004)