Norway Rat

Actual Size: 16” long including the tail

Characteristics: Robust, typically grayish brown, can be reddish-brown to blackish.

Habitat: Known to create 2-3 inch long burrows along property lines and gardens.


  • Also known as the brown rat or sewer rat.
  • Tails are hairy, and shorter than their head and body combined.
  • Prefer to live in underground burrows, basements and tunnels.

Norway Rats in San Juan

Norway rats are stocky, heavy bodied rats and are larger and more aggressive than their cousin the roof rat or black rat. Found throughout the Puerto Rico region, Norway rats are commensal rodents, living near and dependent on the human habitat for survival. Norway rats will eat almost anything, but prefer cereal grains, meats, fish, nuts, and some fruits. Like most rodents, Norway rats are most active an hour after sunset and just before dawn. The gnawing activity of Norway rats can cause considerable damage to homes, gardens and structures. Norway rats are carriers of serious diseases, including jaundice, rat bite fever, and salmonella.

Norway Rat Habitat

In general, Norway rats are ground burrowing animals and construct burrows that are 2 to 3 inches in diameter and up to 6.5 feet in length. Burrows are constructed outdoors along foundations and gardens. Norway rats are nocturnal and will enter homes at night in search of food, returning back to their burrow.  If nests are found inside homes, they are typically in basements and crawl spaces. If a population is large, Norway rats will nest in upper areas of a home or structure.

Norway Rat Behaviors, Threats or Dangers

Norway rats can damage foundations, slabs, garden crops and plants as they burrow and gnaw to find food and shelter. Inside homes, Norway rats may cause extensive damage when nesting in walls and attics. Accounts of rodents starting fires through the gnawing of electrical wires have been widely reported. Chewed, exposed wires inside walls can spark, causing interior walls to catch fire. When foraging for food, these rats consume and contaminate food meant for humans, pets and livestock. Salmonella, leptospirosis, and rat bite fever are among the dozens of diseases spread by Norway rats.

If you have a Norway rat infestation in your San Juan property, always contact a licensed rodent control company.