While most people associate rats with sewers and subterranean burrows, the nesting behavior of these rodents depends entirely on the species involved. One common type is decidedly arboreal. Understanding which rat species is responsible for this high-level activity is the first step in identifying and managing a potential infestation. This article clarifies the differences between the two main domestic rat species and details how to recognize and deal with their tree-based homes.
Which Rat Species Nests in Trees?
Distinguishing between the two most common commensal species—the Norway Rat and the Roof Rat—answers whether rats nest in trees. The Norway Rat (Rattus norvegicus), often called the brown or sewer rat, is a stocky, heavy-bodied rodent built for digging. This species is predominantly a burrower, establishing its nests underground along building foundations, beneath woodpiles, or in basements and crawl spaces.
In contrast, the Roof Rat (Rattus rattus) is responsible for nearly all arboreal nesting activity. Also known as the black rat or ship rat, this rodent possesses a slender body and a tail that is noticeably longer than its head and body combined. This physical characteristic aids its exceptional climbing ability. Roof rats prefer elevated locations, utilizing their agility to travel along utility lines, fences, and tree branches to access high-level nesting sites.
Where and How Arboreal Nests Are Constructed
Roof rats construct their nests in sheltered spots high above the ground, often near a food source and away from predators. Their outdoor nests are frequently found in dense vegetation, thick shrubbery, overgrown vines, and especially within trees. They show a particular preference for the dense crowns of palm trees or the sturdy branches of fruit trees.
The nest itself is typically a messy collection of materials woven together into a spherical or dome shape, measuring four to six inches in diameter. Construction utilizes readily available fibrous debris, including shredded leaves, grass, small twigs, and plant fibers. When nesting near human structures, they may also incorporate materials like shredded paper, cloth, or insulation to create a warm, secure environment for resting and raising their young. This elevated placement provides the security required for a female to safely produce up to five litters per year.
Identifying and Addressing High-Level Infestations
Identifying a high-level rat infestation requires looking for evidence in elevated areas, not just on the ground. Beyond a visible nest in a tree, homeowners should check for high-up travel paths, known as “rat runs.” These often appear as dark, greasy rub marks left along the tops of fences, beams, or utility lines where the rat’s oily fur repeatedly brushes the surface.
Another sign is the presence of small, spindle-shaped droppings, about one-half to three-quarters of an inch long, found on elevated surfaces like patios, decks, or balconies directly beneath a suspected nesting tree. Gnaw marks on high-level items, such as electrical wiring in an attic or fruit still hanging on a tree, also suggest arboreal activity. The sounds of scratching or scurrying in the ceilings or walls just after dusk indicate nocturnal movements as the rats begin their foraging.
Addressing an arboreal infestation begins with habitat modification to remove the rats’ access and shelter. Homeowners should trim all tree branches and thick shrubs so they are at least three feet away from the roofline and walls of the house. Removing dense ground cover and woodpiles, especially those elevated on blocks, eliminates potential secondary nesting sites. Securing all potential entry points into the home, focusing on gaps near the roofline, eaves, and utility penetrations, prevents the outdoor infestation from moving indoors.