The roof rat is the smaller of the 2 commensal rats (Norway rat is larger) and the more common commensal rat in the subtropical and tropical regions of the world. It not only damages/destroys materials by gnawing eats and contaminates stored food but it is also of human health importance as a vector or carrier of disease organisms. Roof rats are usual thought to be of southeast Asia origin and are now worldwide in distribution. In the United Stated it is more common in the coastal states seaports and the southern third of the country.
Adult with combined head and body length 6"-8" (16-20 cm) tail length 7"-10" (19-25 cm) usual weight 5-9 ozs (150-250 g) but up to 12ozs (340 g). Fur soft smooth color usually brown with black intermixed to gray to black above with underside white gray or black.
Roof rats are primarily nocturnal in habit and they are very cautious. Although they constantly explore their surroundings they shy away from new objects and changes. Roof rats prefer to nest in the upper parts of structures but may be found under buildings as well as occasionally in basements and sewers. Outdoors they prefer to nest in higher places such as in trees but may occasionally be found in burrows in or under vegetation around the structure. These are social animals but less so than Norway rats. Several nests may be located within a given area. An opening of greater than 1/2" (12 mm) is required for entry into buildings.