Rats are prolific builders, and they definitively construct nests. Nest building is a fundamental behavior for survival and successful reproduction across various species, including the brown rat (Rattus norvegicus) and the roof rat (Rattus rattus). This instinct drives them to seek out and modify environments to create secure shelter.
Why Rats Construct Nests
The motivation for building a nest centers on biological and behavioral needs for survival. A primary function of the nest is thermoregulation, the ability to maintain a stable internal body temperature. Rats rely on the insulation of a well-built nest to conserve body heat, especially during colder periods.
The nest is also a dedicated site for reproduction and maternal care. Female rats, once pregnant, exhibit strong maternal instincts to gather materials and construct a safe nursery. Rat pups are born altricial, meaning they are hairless, blind, and completely dependent on the mother and the nest’s warmth for their first weeks of life.
Beyond temperature control, a secure nest provides protection from predators and environmental threats. These sheltered locations offer security and seclusion, allowing the rat to rest and rear offspring. The proximity of the nest to food and water sources minimizes the distance a rat must travel, contributing to its overall safety.
Identifying Nesting Materials and Appearance
A completed rat nest is typically a messy, yet deliberately woven, collection of scavenged materials shaped into a shelter. The appearance varies depending on the availability of resources in the immediate vicinity. In human-occupied structures, nests are often composed of shredded paper, cardboard, fabric scraps, and insulation, which provides excellent warmth.
The structure often resembles a loose, spherical or bowl-shaped ball of material, usually ranging from four to six inches in diameter. Nests are constructed for shelter and lined with soft materials, distinguishing them from simple food caches. The presence of droppings or a strong, musky odor around the structure is a reliable indicator that the site is an active nest.
Where Rats Locate Nests
Rats choose nesting locations based on security, warmth, and proximity to resources, leading them to inhabit a range of indoor and outdoor sites. Inside buildings, preferred sites are secluded and undisturbed areas, such as attics where they use insulation as a ready source of material. Wall voids, subfloors, and spaces behind large appliances or in cluttered storage areas also provide ideal darkness and protection.
For outdoor nesting, brown rats frequently establish burrows in the ground, often near the edges of buildings, under sheds, or beneath concrete slabs. These burrows are discreet entry points to a network of tunnels that lead to the nesting chamber.
Roof rats, conversely, tend to nest in elevated locations. They utilize dense vegetation, trees, or high-up areas like eaves and vents.