The principal indoor rat-sized pest in the Eastern part of the country are Old World (exotic) rats. The most common, rat-sized structural pests in the West, are native wood rats, squirrels, and chipmunks.
Both native and exotic rats quickly adapt to nearly all living environments provided them by humans (granaries, fields, sewers, attics, basements, etc.). Old World rats, similar to exotic mice, often live most of their lives inside buildings.
In the West, chipmunks, wood rats, some ground squirrels, and tree squirrels may nest inside buildings, attics, crawlspaces, chimneys, etc. (especially during winter), but usually feed outside and seldom enter occupied portions of a building.
Old World female rats become reproductively mature when about 3 months old and can produce an average of 20 surviving young per year. Native rat-size rodents are less productive than mice but females can usually raise 3 to 4 surviving young each year.
Rats eat the same general foods as do mice but, being larger animals, require about 1-ounce (2 tablespoons) of food and 2 to 1-ounce of water per day for survival. Like mice, a water supply is not as critical as food because most water comes from their food.
Old World rats are very agile and can leap 3-feet straight up or 4-feet horizontally. They can also climb the outside of a 3-inch diameter pipe, walk on wires between buildings, swim 1/2-mile of open water, tread water for days, swim up-current in sewer lines and through toilet traps, and survive a fall of more than 50-feet. Native rats (tree squirrels, wood rats, chipmunks, and some ground squirrels) are also very agile.
Rats have powerful teeth and are able to gnaw holes through concrete block, aluminum siding, adobe brick, wall board, plaster, wood, and various other durable materials. Usually, there must be an exposed edge to gnaw; smooth surfaces limit their ability to initiate holes.
Although rats are much larger animals than mice, they can squeeze through holes only ½-inch in diameter.
Old World rats usually range within about 100 to 150-feet of their nest. They may sometimes nest indoors and forage outside for food – or – live outside and forage indoors. Native rats have relatively large forage areas and can move long distances from an indoor nest site to a food source.
– Remove as much grass, weeds, and debris as possible from around buildings. These provide food sources and harborage sites for rodents.
– If possible, maintain an 18-inch wide, vegetation-free zone around buildings. Continually clean up all outside and inside clutter/litter.
– Trim the bottoms of hedges and other ground-hugging plants up from the ground to eliminate rodent harborage. Trim plants that touch or overhand buildings back 3 to 4-feet.
– Promptly repair all water leaks.
– Store firewood, lumber, rubbish, equipment, construction materials, and other items on pallets raised at least 18-inches off the ground and located at least 30 feet from buildings, walls, and fences.
– It is better to place exterior lighting on poles out and away from structures and shine the light back onto buildings from a distance. This prevents the attraction of night-flying insects which can serve as a food source for rodents.