Rats

Rats are some of the most problematic rodents in the US.  They consume and contaminate food, damage structures and property, and transmit parasites and diseases to other animals and humans.  In California, the most common rats are the roof rat and the Norway rat. For effective trapping, it is important to know which rat species are present. 

Norway Rats (Rattus Norvegicus)

The Norway Rats aka brown rat or the sewer rats, they are stocky burrowing rodents that are larger than roof rats.  The Norway rat is large and robust, with a blunt muzzle, small ears, and is mostly gray in color.  They burrow along building foundations, under rubbish and woodpiles and in moist areas around gardens and fields.  When they invade a structure, they generally stay at ground level or the basement.  Their nests are usually lined with cloth, shredded paper, or fibrous materials.  Norway rats eat a wide variety of foods but prefer to eat cereal grains, meats, fish, nuts and some fruits.  When scavenging for food and water, the Norway rat usually does not travel further than 100-150 feet in diameter, seldom do they travel further than 300 feet from their burrow or nest.  Norway rats and roof rats do not get along.  The Norway rat is larger than a roof rat, and the more dominant of the two species, it will kill a roof rat in a fight.  The Norway rat has an average of four to six litters per year and may successfully wean 20 or more offspring per year.  Norway rats are found throughout the contiguous United States.

Roof Rats (Rattus rattus)

Roof rats are slightly smaller than the Norway Rats and are sometimes called the black rats.  Unlike Norway rats, their tails are longer than their heads and bodies combined.  Roof rats are very agile climbers and usually live and nest above ground in shrubs, trees and dense vegetation.  Roof rats are sleek, have a pointed muzzle, long ears, and are grey to white in color.  When they invade structures, they are most often found in the attics, walls, false ceilings and cabinets.  The Roof rat also eats a wide variety of foods, but mostly prefers to eat fruits, nuts, berries, slugs and snails.  Roof rats enjoy eating avocadoes and fresh fruit still on the trees.  When scavenging for food and water, the roof rat routinely travels to up 300 feet.  Roof rats have an excellent sense of balance and use their long tails for balance while traveling along utility lines.  They move much faster than the Norway rat and are very agile climbers, which helps them quickly escape predators.  The roof rat has about three to five litters each year, having five to eight offspring per litter.  The roof rat has a more limited geographical range; they prefer ocean-influenced, warmer climates. Both Norway and Roof rats gain entry to structures by gnawing, climbing, jumping, or swimming through sewers and entering through the toilet or broken drains.  The Noway rat is a much better swimmer, and the Roof rat are more agile and better climbers.  Rats, especially young rats (young rats are often confused with the house mouse), can squeeze through a gap of only ½ inch.