d. Burrows. Burrows may be used as nesting or hiding places or as a means of
entrance to buildings. The former are usually 12 to 18 inches deep, and they may
extend several feet in a horizontal direction and connect with other burrows and
entrances. Rats have been known to burrow almost 4 feet vertically in order to pass
under a foundation wall. Active burrows frequently have a pile of newly excavated soil
at the entrance; abandoned holes often are closed with undisturbed cobwebs. A sign of
use on relatively compact soil is the absence of dust or loose earth, and on loose soil, a
more compacted appearance than the surrounding area and the presence of distinct
tracks. Burrows will be found along the outside wall of buildings, in dirt basement floors,
and around many of the outbuildings of a business premise, residence, or farm. Away
from buildings, burrows may be found in embankments, hedge rows, fills, and under
e. Nests. Rat nests may be found in concealed spots in wasteland, in the
corners of cultivated fields, in trees, and in buildings; that is to say, wherever rats find
shelter and concealment. The apparent freshness of the material from which the nest is
constructed and the age of droppings and food scraps nearby is of some assistance in
determining whether the nest currently is used.
f. Gnawings. Evidence of recent gnawings is one of the most reliable signs of
rodents. A recently gnawed area will be sharp and may show individual tooth marks.
These edges become rounded and darkened in a few days, and the small cuttings are
soon scattered or swept away. Rats will smooth and enlarge a hole through which they
pass, so that is smoothness and enlargement will be an indication that the hole is an old
or much traveled route. Young rats can pass through a 3/4-inch opening, and any rat
easily can enlarge an opening and pass through the spaces beneath wooden sills,
doors, and windows unless these are shielded with metal.
g. Damage. (See figure 2-3). Damage to foodstuffs and other goods may
constitute the only visible evidence of rat infestation. Rats often will carry small pieces
of food into accessible places such as beneath stoves and refrigerators, and these may
be taken as a good indication of their presence.
Figure 2-3. Rat damage to subsistence supplies.