A rat is a medium-sized, long-tailed rodent, distinguished from mice by size. While the term “rat” is often used broadly, true rats belong primarily to the genus Rattus, which originated in Asia. These animals are known for their adaptability and thriving in diverse environments alongside humans. There are 56 species of rats within the Rattus genus; many other rodent species are also called rats.
Rats Across the Globe
Rats have spread across nearly every continent, establishing populations wherever humans reside. The only continent free of rats is Antarctica, due to its extreme cold and lack of human habitation that would provide shelter and food. Their global expansion occurred through human migration and trade routes, with species like the black rat and brown rat stowing away on ships to reach new territories. This has made them among the most widespread and successful invasive mammals globally.
Key Rat Species and Preferred Habitats
Among many species, the Norway rat (Rattus norvegicus) and the roof rat (Rattus rattus) are two of the most common and widely distributed. These species exhibit distinct habitat preferences due to their behaviors and physical characteristics. Understanding these preferences aids identification.
The Norway rat, also known as the brown rat or sewer rat, is a stocky, burrowing rodent. It has a tail shorter than its head and body combined. These rats prefer to live at ground level, constructing burrows under buildings, concrete slabs, along stream banks, and in garbage dumps. They are frequently found in urban and suburban areas, inhabiting cellars, basements, warehouses, and sewers, and common on farms in barns and granaries. While they can climb, Norway rats generally stay on lower floors of multi-story buildings.
The roof rat, also called the black rat or ship rat, is more slender than the Norway rat, with a tail longer than its head and body. As their name suggests, roof rats are arboreal, preferring elevated locations. They are often found in attics, rafters, eaves, and on roofs of homes, as well as in various trees. Outdoors, they nest in dense vegetation and woodpiles, using their climbing agility to navigate power lines and fences.
What Shapes Rat Habitats
Several factors influence where rat populations establish and thrive, often linked to human activity and environmental conditions. Food and water availability is a primary determinant; rats are opportunistic omnivores consuming diverse plant and animal matter. They frequently rely on human waste, stored food, and pet food, but also forage for natural sources.
Shelter and harborage are important for rat survival, providing protection from predators and the elements. Buildings, debris, dense vegetation, and burrows offer ideal nesting sites. Urbanization plays a significant role, with infrastructure like sewers, utility lines, and discarded materials creating extensive networks of shelter and food sources. Climate influences distribution, though rats are adaptable and can survive in diverse temperature ranges, except for extreme cold.
Why Understanding Rat Distribution Matters
Understanding the global distribution and habitat preferences of rats is important for public health and pest management. Rats are known vectors for numerous diseases, including leptospirosis, hantavirus, and salmonellosis. Knowing where rat populations are concentrated helps public health officials implement targeted prevention and control, reducing disease transmission.
Knowledge of rat habitats is also important for effective pest control strategies. Identifying the specific species and its preferred living areas allows for precise and effective eradication or management efforts. For instance, methods for ground-dwelling Norway rats differ from those used for arboreal roof rats.
Economically, rats cause substantial damage through gnawing on structures, wires, and pipes, and by contaminating food supplies. The estimated annual economic loss due to rodents in the U.S. can reach billions of dollars. Furthermore, rats can have negative ecological impacts, especially as invasive species on islands, where they prey on native wildlife, including birds and their eggs, and compete for resources.