As the rat family grows, more burrows are built, resulting in a network of underground tunnels. Inside, the Norway Rat commonly nest on the lower levels, but if the population is too large, they may be found in the attic and ceiling areas. Their nests are built from soft material like paper or grass chewed into small pieces. Rats will climb if necessary to enter a building, the Norway Rat is an excellent swimmer. Rats are suspicious of changes in the environment or new foods, for this reason it may take a couple of days for traps or poison baits to take.
Rats are nocturnal, with their peak activity at dusk or before dawn.
When the population is large or they are disturbed or hungry, you can see activity during the day. The Roof Rat is smaller and more slender than the bigger Norway Rat. The tail is longer than the head and body combined. They have large ears and a pointed nose. Refer to the section on Norway Rat inspection.