Rats definitely exist in Colorado, but the situation is nuanced by the species involved. The state is home to both ecologically important native rodents often called rats, and introduced, commensal species associated with human infrastructure. Understanding the difference between these two groups is necessary for proper identification and management, as their behaviors and preferred habitats vary significantly across the diverse Colorado landscape. This distinction separates the wildlife that plays a natural role in the ecosystem from the pests that pose a challenge to urban and suburban living.
The Two Categories of Rats in Colorado
The rodents often referred to as “rats” in Colorado fall into two distinct biological and ecological categories. The first group consists of native species, primarily the woodrats of the genus Neotoma, which are natural components of the state’s wildlife. These animals are generally found in rural, mountainous, and high-desert environments, where they contribute to the local ecosystem. The second category includes non-native, introduced species, namely the Norway rat and the roof rat. These species are closely associated with human habitation, thriving in urban and suburban settings, making them the primary source of pest concerns for residents along the Front Range.
Native Species: Woodrats (Packrats)
Native woodrats, commonly known as packrats, are found throughout Colorado, particularly in rocky, broken terrain, canyons, and mesa walls. The state is home to at least six species, including the bushy-tailed woodrat (Neotoma cinerea), which is one of the largest, sometimes exceeding 16 inches in total length. These rodents are easily distinguished from their invasive counterparts by their large ears, prominent eyes, and a noticeably furry tail.
A defining characteristic of the woodrat is the construction of its “midden,” an elaborate den built from collected materials like sticks, rocks, bones, and plant matter. These middens are cemented together by crystallized urine, creating structures that can be utilized by generations of woodrats over many years. Researchers use ancient, fossilized middens as environmental time capsules, dating back tens of thousands of years, to reconstruct past climates and vegetation patterns.
The woodrat’s nickname, “packrat,” stems from its habit of compulsively collecting objects to fortify its den and cache food. They have a peculiar tendency to drop whatever item they are currently carrying if they encounter something more appealing. While they occasionally seek shelter in abandoned buildings or attics, they are wild animals that primarily inhabit areas away from dense human population centers.
Invasive Species: Norway and Roof Rats
The most significant rodent pests in Colorado are the invasive Norway rat (Rattus norvegicus), also called the brown rat or sewer rat. These rodents are stocky and robust, with adults typically reaching a total length of 16 to 21 inches, including their tail. They have small ears and eyes relative to their head size, a blunt muzzle, and a tail that is shorter than the length of their head and body combined.
Norway rats are burrowing specialists, preferring to inhabit ground-level areas such as basements, crawl spaces, and sewer systems. They are particularly prevalent in Colorado’s urban centers, including Denver and Colorado Springs, where they exploit human waste and structural weaknesses for food and shelter. Signs of an infestation include large, capsule-shaped droppings with blunt ends, and burrows excavated near foundations and under debris piles.
Roof Rats
Roof rats (Rattus rattus), also known as black rats, are less common across the entire state but are occasionally found in urban areas. They are more slender and smaller than the Norway rat, with a pointed muzzle and a tail that is longer than their head and body combined. These rats are agile climbers, preferring elevated nesting sites in attics, rafters, and high wall voids.
Infestations of either invasive species are identified by greasy rub marks along their established travel paths, known as runways, and gnaw marks left on various materials. Norway rats leave larger, more destructive marks, while roof rats leave finer, smaller markings due to their sharper incisors. Sealing entry points larger than a quarter-inch is necessary to exclude both roof rats and Norway rats from structures.
Health Concerns Associated with Colorado Rodents
Rodents in Colorado, both native and invasive, can carry zoonotic diseases that pose a risk to human health. One significant concern in the region is Hantavirus Pulmonary Syndrome, a rare but severe respiratory illness. Hantavirus is primarily carried by the deer mouse, a native rodent, and is transmitted when people inhale aerosolized particles from the urine, droppings, or saliva of an infected animal.
Another serious disease endemic to Colorado is the Plague, caused by the bacterium Yersinia pestis. Plague is typically transmitted to humans through the bite of infected fleas that have fed on wild rodents such as woodrats, ground squirrels, and prairie dogs. Human cases of plague are reported in Colorado, most often in the warmer months when rodent and flea activity is high.
When cleaning areas contaminated with rodent droppings or nests, caution is necessary to avoid inhaling potentially infectious particles. It is advisable to air out the space for at least 30 minutes before entering and to avoid sweeping or vacuuming dry materials. Contaminated areas should be soaked with a disinfectant solution for several minutes before cleanup to neutralize pathogens and prevent them from becoming airborne.