Rodents make up 40 percent of all extant mammalian species that have been documented worldwide, and some of the most well known rodent groups include squirrels, voles, muskrats, prairie dogs, beavers, chipmunks, and of course, rats and mice. Of the more than 1,500 extant rodent species that have been documented worldwide, many are capable of transmitting disease to humans, and some are known pests of structures, cultivated landscapes, and/or agricultural crops. For example, beavers, chipmunks, and prairie dogs are all known for excavating ground soil in ecologically fragile or cultivated landscapes like gardens, lawn-grass, and golf courses. However, with the occasional exception of squirrels, the only rodents that make a habit out of regularly infesting homes and buildings are certain rat and mouse species.
Rodents include all mammalian species that belong to the Rodentia order, and experts believe the first rodents to exist emerged around 54 million years ago. The two rat pest species that frequently infest homes and buildings in central Texas each belong to the Rattus genus in the Muridae family. The Rattus genus is believed to have emerged between three and six million years ago, and the two Rattus species that are abundant pests in much of the world today diverged from one another to become their own species around 500,000 years ago. These two species are commonly known as Norway rats (Rattus norvegicus) and roof rats (Rattus rattus), and the former is the most common and widespread rat species in the US. Although Norway rats outcompete roof rats for resources in urban areas, both of these species frequently infest homes and buildings in central Texas.
To the casual observer, Norway rats and roof rats look alike, as they each have a similar fur color and body size. However, while roof rats have a uniformly dark grey or black fur coat and an unkempt appearance, Norway rats have a similarly colored, but smoother looking fur coat that features a white patch on the underbelly. Also, Norway rats are 8 to 10 inches in length, while roof rats are 7 to 8 inches in length. Due to their commonality in urban areas, Norway rats are well known for nesting with ground burrows on properties and for invading homes from the ground surface by squeezing beneath door gaps, accessing crawl spaces, and in rare cases, traveling into homes through sewer pipes. Roof rats, on the other hand, prefer to forage and nest above ground in trees, on structures and other elevated locations. Because of their foraging and nesting behavior, roof rats usually invade homes through attic vents, gaps around utility openings on walls, and upper story windows. Once they gain access indoors, roof rats tend to establish concealed harborages in attics, while Norway rats usually remain on the ground floor within wall voids, crowded storage areas, and within crawl spaces.
Have you ever found signs of rat activity within your attic?