Colorado is home to both invasive Norway rats (brown rats) in urban areas and native woodrats (packrats) in wilder terrain. If you’ve spotted a rat on your property, knowing which type you’re dealing with changes everything about how you respond, what risks it poses, and what the law allows you to do about it.
Norway Rats: Colorado’s Urban Pest
Norway rats are non-native to the United States and are found across Colorado, particularly in cities and suburbs. They’re the classic pest rat: stocky, brownish-gray, with a blunt nose and a thick, scaly tail shorter than their body. They thrive near human food sources and shelter, burrowing under foundations, in alleys, and around dumpsters.
Their presence in the wild is harmful to native ecosystems, especially birds. Because they’re classified as a non-native pest species, Colorado Parks and Wildlife does not manage them. That means dealing with Norway rats falls entirely on property owners, pest control services, and local health departments.
Woodrats: Colorado’s Native “Packrats”
The bushy-tailed woodrat is Colorado’s most recognizable native rat. Unlike Norway rats, woodrats are a natural part of the state’s ecosystem and behave very differently. They’re found in rocky environments like talus slopes, boulder fields, rock outcrops, cliffs, and caves. In northwestern Colorado, researchers have also documented them in the floodplain habitats along the Green and Yampa rivers, especially in areas with mature cottonwood trees and woody debris.
Woodrats are primarily nocturnal, most active in the half hour after sunset and again at dawn. They live in small, widely separated family groups. Males are territorial and aggressively defend their dens and foraging areas, while females tend to stay on the same rock outcrop year after year. Young males are the travelers, dispersing to find new den sites.
Their dens are elaborate structures built from sticks, leaves, bark, stones, and sometimes human artifacts (hence the “packrat” nickname). A den is almost never built in the open. It’s anchored against a bush, rock crevice, or tree, and inside it contains tunnels, chambers, and passages. Some chambers hold nests, others are used for food storage. A woodrat may use the same den for its entire life. The nest itself is a small cup-shaped structure about 6 to 8 inches across, made from shredded plant fibers. Woodrats also dry food on rocks before storing it in middens at the edges of their dens, typically stocking up in late August and September.
How to Tell Them Apart
If you’re seeing a rat near your home, garage, or trash, it’s almost certainly a Norway rat. They have coarse brown or gray fur, small ears relative to their head, and a heavy build. Woodrats are lighter in color, have larger ears, softer fur, and a distinctive bushy tail (in the case of the bushy-tailed species). The location matters too: a rat in your basement or near a restaurant is a Norway rat. A rat in a rocky hillside cabin or mountain shed is more likely a woodrat.
Disease Risks From Colorado Rodents
Both types of rats carry health risks, but the biggest concern in Colorado comes from a different rodent entirely: the deer mouse, which is the primary carrier of hantavirus in the United States. Hantavirus pulmonary syndrome is rare but serious, and Colorado reports cases every year. It spreads by breathing in dust contaminated with rodent urine, droppings, or saliva, by handling rodents or nests without protection, or in rare cases through bites.
Norway rats can transmit other diseases through their droppings and urine, and they contaminate food supplies. Plague, carried by fleas on various rodents, also occurs in Colorado. Any time you’re cleaning up rodent droppings or disturbing a nest, wear gloves and a mask, wet the area down before sweeping to avoid stirring up dust, and ventilate enclosed spaces before entering.
Trapping and Removal Laws
Colorado law allows property owners (or their employees and agents) to hunt, trap, or take rats that are damaging property without a license. For Norway rats and mice specifically, you can use body-grip traps (snap traps) without a permit. For all other wildlife, the only legal trap type is a live cage or box trap.
Here’s the critical detail many people miss: if you catch a small game animal or furbearer in a live trap, you cannot relocate it. Colorado law requires that it be killed or released on site. If you want to relocate any species other than tree squirrels, cottontail rabbits, or raccoons, you need a relocation permit from Colorado Parks and Wildlife. This matters if you’re catching native woodrats rather than Norway rats. Woodrats are wildlife, not an unmanaged pest species like Norway rats, so handling them comes with different legal obligations.
Keeping Rats Out
For Norway rats, prevention centers on removing what attracts them. Secure garbage in heavy bins with tight lids. Don’t leave pet food outside overnight. Seal gaps larger than half an inch around foundations, pipes, and vents with steel wool, hardware cloth, or metal flashing. Rats can’t chew through metal. Trim vegetation away from your home’s exterior so rats lose cover near entry points. Eliminate water sources like leaky hoses or birdbaths near the foundation.
For woodrats in mountain cabins or rural sheds, the approach is similar but the context is different. Seal openings, remove nesting material, and store items in hard-sided containers. Because woodrats are attracted to shiny objects and loose materials, keeping storage areas tidy makes your space less appealing as a den site. If a woodrat has already built a den inside a structure, clean it out carefully with proper respiratory protection, especially in enclosed spaces where hantavirus-contaminated dust from any rodent species could be present.