No species in the genus Rattus, the group most people picture when they hear the word “rat,” evolved in North America. Brown rats and black rats both arrived on European ships during the colonial era. But North America is home to a surprisingly rich lineup of native rodents that carry the common name “rat,” including woodrats, cotton rats, rice rats, and kangaroo rats, all of which have lived on the continent for thousands to millions of years. The distinction between these native animals and the introduced species they now share the landscape with turns out to matter for public health, conservation, and even climate science.
Brown Rats and Black Rats Are Imports
The two rat species that infest cities, contaminate food supplies, and generally earn rats their bad reputation are both Old World natives. Black rats (Rattus rattus) are thought to have originated in tropical Asia and spread through the Mediterranean world centuries ago. Brown rats (Rattus norvegicus) likely originated in northern China and central Asia. Both species are commensals, meaning they thrive in close association with humans, and both rode European trade networks to every inhabited continent.
In North America, the timeline of their arrival has recently been sharpened by archaeological work. Researchers analyzing rat remains from eastern North American sites dating from the 1550s through 1900 found that brown rats arrived earlier than historians had assumed and rapidly displaced black rats in coastal urban areas. This replacement happened even though the two species occupy different positions in the food web: black rats tend to eat more plant material, while brown rats are more omnivorous and aggressive. The study provided the earliest molecularly confirmed brown rat specimen in the Americas and traced a pattern in which brown rats systematically outcompeted black rats in one port city after another along the eastern seaboard.1PubMed Central. The ratting of North America: A 350-year retrospective on Rattus species compositions and competition
Before those ships arrived, no member of the genus Rattus had ever set foot on the continent. The ecological slot that brown and black rats now dominate, scavenging human food waste in dense settlements, was essentially empty. Native rodents had their own niches, but none had co-evolved with dense human habitation the way Old World rats had over millennia alongside Eurasian civilizations.
Woodrats, the Continent’s Original “Rats”
The most widespread group of native animals commonly called rats in North America is the woodrat, genus Neotoma. There are roughly two dozen woodrat species spread across the continent, from the deserts of the Southwest to the Appalachian mountains and the Florida Keys. They are sometimes called packrats because of their compulsive habit of collecting objects and building elaborate stick nests, or middens, from whatever materials they can find. These animals look superficially similar to brown rats in size, but their behavior, diet, and ecology are fundamentally different. They tend to be solitary, herbivorous, and tied to specific habitat types rather than human structures.
In the arid landscapes of the American West, woodrats function as ecosystem engineers. Species like the southern plains woodrat (Neotoma micropus) and the white-throated woodrat (N. albigula) build above-ground stick nests using material gathered from within about a 50-meter radius. These middens change the soil beneath them: researchers working in the Chihuahuan Desert found that decaying midden material increased soil moisture and accelerated decomposition of surrounding plant litter, creating small patches of enriched soil in otherwise dry, nutrient-poor terrain.2ScienceDirect. Decaying woodrat (Neotoma spp.) middens increase soil resources and accelerate decomposition of contemporary litter In a landscape where water and nutrients are scarce, these pockets of fertility support different plant communities and decomposer organisms than the surrounding desert floor. Woodrats, in other words, are quietly reshaping the ecosystems they live in.
Cotton Rats, Rice Rats, and Kangaroo Rats
Woodrats get the most attention, but several other native rodent groups also carry the common name “rat” in North America. Each occupies a distinct ecological niche, and none is closely related to the invasive Rattus species.
The hispid cotton rat (Sigmodon hispidus) is one of the most abundant small mammals in the grasslands and old fields of the southeastern and south-central United States. Cotton rats are stocky, short-tailed rodents that live in dense herbaceous cover and feed mainly on grasses and seeds. Their populations can boom and bust dramatically depending on food availability and predation pressure. In experimental grassland plots, researchers found that cotton rat survival and reproductive success increased when predators were excluded, suggesting that predation is a major force shaping their populations in the wild.3Canadian Journal of Zoology / PubMed Central. Population dynamics of hispid cotton rats (Sigmodon hispidus) across a nitrogen-amended landscape
The marsh rice rat (Oryzomys palustris) is a semiaquatic species found in wetlands across the southeastern United States and along the Atlantic Coast. Rice rats are strong swimmers that feed on aquatic organisms and wetland vegetation. Studies in southern Illinois found that most rice rats were captured in permanent or semipermanent emergent wetlands or in roadside ditches running through wetland patches, with dense low herbaceous cover being the strongest predictor of their presence.4Journal of Mammalogy. Habitat associations of the marsh rice rat (Oryzomys palustris) in freshwater wetlands of southern Illinois When rice rats do turn up in adjacent upland areas, those habitats appear to function mainly as overflow zones for dispersing animals or as refuges during high tides, not as primary foraging grounds. Their diet in uplands still consisted mostly of aquatic organisms and wetland plants rather than upland vegetation.5Journal of Mammalogy. Use of Tidal Marsh and Upland Habitats by the Marsh Rice Rat (Oryzomys palustris)
Kangaroo rats (genus Dipodomys) are probably the most visually distinctive of the native “rats.” They have enormous hind legs, tiny front legs, long tufted tails, and external fur-lined cheek pouches for carrying seeds. They move by bipedal hopping and are adapted to some of the driest environments on the continent. Merriam’s kangaroo rat, for example, can survive without ever drinking water, obtaining all the moisture it needs from metabolizing dry seeds. Laboratory studies found that when given a choice of temperatures, kangaroo rats consistently selected conditions that minimized energy expenditure rather than water loss, suggesting that their water-conservation adaptations are so effective that energy, not hydration, is the more pressing constraint on their survival.6PubMed Central. Merriam’s kangaroo rats (Dipodomys merriami) voluntarily select temperatures that conserve energy rather than water
None of these animals are in the same family as brown or black rats. The common name “rat” is applied loosely in English to any medium-sized rodent with a long tail. Biologically, a cotton rat is about as closely related to a brown rat as a hamster is.
Fifty Thousand Years of Packrat Climate Records
One of the more unexpected contributions of native rats to science comes from the woodrat habit of building middens. In the arid West, the plant material, seeds, and other debris that woodrats pack into their nests becomes cemented together by crystallized urine, which in dry cave environments can preserve organic material for tens of thousands of years. These ancient middens are treasure troves for paleontologists and climate scientists.
By identifying the plant species preserved in middens of different ages, researchers can reconstruct what the local vegetation looked like at the time the midden was built, and from that, infer what the climate was. A large-scale analysis of more than 600 individual paleomiddens spanning the past 50,000 years generated quantitative climate estimates from plant community composition across western North America.7Open Quaternary. Quantitative Late Quaternary Climate Reconstruction from Plant Macrofossil Communities in Western North America The record shows dramatic shifts: plant communities that now live at high elevations were growing at much lower altitudes during glacial periods, desert scrub expanded during warm dry intervals, and the boundaries between biomes shifted hundreds of kilometers over time. Without packrats obsessively hoarding plant material and urinating on it in dry caves, much of this record would not exist. It is one of the richest terrestrial paleoclimate archives in the world for the regions where woodrats live.
How Invasive Rats Threaten Native Species
The arrival of Rattus species in North America set off ecological changes that are still playing out. Invasive rats compete with native rodents for food and shelter, prey on eggs and nestlings of ground-nesting birds, and alter plant communities by consuming seeds and seedlings. But the most acute threats to native rat species often come from a combination of invasive predators, habitat loss, and disease rather than from direct competition with Rattus alone.
The Key Largo woodrat (Neotoma floridana smalli) is a case in point. This endangered subspecies is found only in the tropical hardwood hammock forests of Key Largo, Florida, and it has undergone drastic population declines over the past several decades. Habitat loss from development is one factor, but exotic predators, particularly feral cats, have been devastating. Removal of exotic predators from woodrat habitat led to measurable improvements in the species’ distribution and behavior, a strong signal that predation rather than habitat quality alone was suppressing the population.8Biological Conservation. Towards recovery of an endangered island endemic: Distributional and behavioral responses of Key Largo woodrats associated with exotic predator removal The Key Largo cotton mouse, another endangered rodent endemic to the same patch of forest, faces the same combination of threats.9Global Ecology and Conservation. Varying responses of co-occurring endangered rodents to forest age, human disturbance, and invasive competitors in the Florida Keys
Farther north, the Allegheny woodrat (Neotoma magister) has vanished from the northern portions of its historical range in the Appalachian region. A leading suspect is raccoon roundworm (Baylisascaris procyonis), a common intestinal parasite of raccoons that is highly dangerous to other animals that accidentally ingest its eggs. Woodrats, which forage on the ground and sometimes investigate raccoon latrines, are vulnerable to picking up the parasite. In reintroduction experiments, woodrat populations released into sites with heavy raccoon-latrine contamination died off significantly faster than populations released into cleaner sites, with a strong negative relationship between the number of raccoon latrines and woodrat persistence.10Conservation Biology. Trophically Transmitted Parasites and the Conservation of Small Populations: Raccoon Roundworm and the Imperiled Allegheny Woodrat Efforts to manage the problem have included distributing anthelmintic bait to reduce parasite loads in raccoon populations.11The Journal of Wildlife Management. Management of raccoon roundworm in free‐ranging raccoon populations via anthelmintic baiting
Native Rodents and Suburban Sprawl
Even where invasive rats and exotic predators are not the immediate problem, native rodent populations face pressure from the simple expansion of suburban development. A study of rodent communities in open-space grasslands adjacent to suburban neighborhoods in Colorado found that native species, including deer mice and hispid pocket mice, were captured far more often in the interior of grassland patches than on the edges near suburban development. For every native species examined, the plots with the highest capture rates were in landscapes that were less than about ten percent suburbanized. The researchers concluded that proximity to suburban landscapes had a strongly negative effect on native rodent abundance in open-space grasslands.12Conservation Biology. Patterns of Rodent Abundance on Open‐Space Grasslands in Relation to Suburban Edges
The pattern is worth pausing on. It is not that suburban neighborhoods are hostile in the way a parking lot is hostile; the grassland patches still existed and still looked like habitat. But something about the edge effect, whether increased predation by domestic cats, competition from non-native rodents like house mice, altered vegetation, artificial lighting, or some combination, made those boundary zones inhospitable to native species. House mice, an introduced species, showed no preference for edges or interiors. They were equally at home throughout. This is a recurring theme in invasion ecology: generalist invasive species tolerate human-modified landscapes that native specialists cannot.
Why the Confusion Persists
Part of the reason people assume there are no native rats in North America is that the word “rat” has become almost synonymous with the brown rat in everyday English. When someone says “I saw a rat,” they mean the large, gray-brown animal rummaging through trash in an alley, not a woodrat perched on a cliff ledge in Utah or a rice rat swimming through a salt marsh in Georgia. The cultural dominance of Rattus norvegicus in urban life has effectively erased public awareness of native species that share the common name.
This matters beyond trivia. When people conflate all rats with invasive urban pests, it becomes harder to build public support for conserving species like the Key Largo woodrat or the Allegheny woodrat. These animals face genuine extinction risk, but the word “rat” in their name triggers disgust rather than concern. Conservation biologists working with endangered woodrats sometimes note that the public-relations challenge of saving anything called a rat is steeper than the biology warrants. Woodrats do not infest homes, do not carry the same suite of diseases associated with brown rats, and do not thrive in human garbage. They are shy, solitary herbivores that build elaborate nests in rocky outcrops and desert scrublands. The only thing they share with the reviled city rat is a few syllables in their common name.
Native Rats and Disease
The disease question is another area where the native-versus-invasive distinction matters. Brown and black rats are infamous vectors for a long list of human pathogens, from plague to leptospirosis to hantavirus (though in North America, hantavirus is more commonly associated with native deer mice than with Rattus). A review of rats as hosts of infectious agents emphasized the importance of distinguishing between the roles rats play as disease reservoirs in their regions of evolutionary origin versus the roles they play in regions where only one or two rat species were recently introduced by human activity.13PubMed Central. Aboriginal and invasive rats of genus Rattus as hosts of infectious agents In their native Asian range, dozens of Rattus species coexist with a complex web of pathogens that have co-evolved with them. In North America, the two introduced Rattus species brought a subset of those pathogens into ecosystems that had never encountered them, while also picking up new ones from the local environment.
Native North American rodents carry their own pathogens, of course. Deer mice are the primary reservoir for Sin Nombre hantavirus in the western United States, and cotton rats can carry certain arenaviruses. But the disease profile of native rodents is different from that of invasive Rattus, and the public health strategies for managing each are different too. Lumping all “rats” together in disease-control messaging leads to misdirected effort. Controlling urban brown rat populations in a coastal city is a fundamentally different task from managing hantavirus risk in rural areas where deer mice enter cabins and sheds.
How Many Native “Rat” Species Are There?
Counting depends on where you draw the line on the word “rat.” If you include every North American rodent that has “rat” somewhere in its common name, the list is long. The woodrat genus Neotoma alone contains roughly 20 to 25 species depending on how taxonomists split them, ranging from the bushy-tailed woodrat of the Pacific Northwest to the desert woodrat of the Sonoran region. Cotton rats in the genus Sigmodon add another handful of species, mostly in the southern tier of the continent and into Central America. Rice rats (Oryzomys and related genera) contribute several more, primarily in wetland habitats. Kangaroo rats in the genus Dipodomys number around 20 species across the arid West. There are also banner-tailed kangaroo rats, Ord’s kangaroo rats, giant kangaroo rats (which despite the name weigh only about 130 grams), and others.
If you restrict the question strictly to the genus Rattus, the answer is zero: no Rattus species is native to the Americas. Every member of that genus on the continent is an introduced colonial-era arrival or later stowaway. But if you ask whether North America has native animals called rats that fill important ecological roles, the answer is an emphatic yes, and dozens of species at that. They pollinate nothing, they are not cuddly, and they will never be mascots, but they build structures that reshape desert soils, preserve climate records spanning 50,000 years, serve as prey for hawks and owls and snakes, and maintain the web of ecological interactions that holds wild landscapes together.