The Norway rat is the largest of the commensal (i.e., living in
close association with humans) rodents. The head and body are
seven to ten inches long and the tail is an additional six to
eight inches. It has a stocky body and weighs seven to 18 ounces.
The fur is coarse, shaggy, and brown with some black hairs. The
muzzle is blunt, eyes and ears are small, and the tail, which
is bi-colored, is shorter than the head and body combined. Norway
rat droppings are up to 3/4. inch long with blunt ends.
Rats are nocturnal. They are shy about new objects and very
cautious when things change in their environment and along their
established runs. Outdoors, Norway rats prefer to nest in burrows
in the soil, e.g., under sidewalks and concrete pads, stream/river
banks, railroad track beds, next to buildings, in low ground
cover, etc. The burrows typically have one main entry hole and
at least one escape hole. The rats easily enter buildings through
1/2-inch and larger gaps. In buildings they prefer to nest in
the lower levels of the building, e.g., crawlspace, basement,
loading dock and sewers. They prefer foods such as meat, fish,
and cereals and require a separate nonfood water source. Their
foraging range is 100 to 150 feet from their nest. Rats are
associated with various diseases and occasionally bite. Plague
is of little concern because it has not occurred in rats in
the United States for many years. However, leptospirosis is
vectored by rats, and, thus, is a disease of great concern.
This disease is acquired by eating food and drinking water which
are contaminated with infected rat urine. Rats also cause significant
structural damage and product destruction.