Organisation: United States Department of Agriculture (USDA)
As rats and mice move around in their living environment, moving from food sources to their nests and shelter, they leave behind characteristic traces that betray their presence; these are called rodent signs and are useful in determining the presence and degree of rodent infestation inside structures. Since rats and mice are secretive and come out after darkness, we rarely see them directly. However, family members of farm households should be aware of rodents in the farm structures, since in their daily activities they should see signs of rodents. Especially at night, they should be aware of the foraging activities of rodents in the household, sighting them in the structures or hearing their squeaks, gnawings, and rustlings. Some of the evidence observers should look for are detailed below.
Faecal droppings are found wherever rodents are active - along their pathways, near walls, and near food and shelter. If the droppings are of several sizes it may indicate animals of different ages or it could indicate an infestation of several species of rodents. Rat droppings are usually 10-15 mm in length, while those of mice are only 3-6 mm long. Numbers of droppings are not very useful in estimating the size of the infestation, since they may have accumulated over a considerable period of time. However, if the area is swept clean and examined the next day, some idea of numbers may be estimated. In general, roof rats make 37-60 droppings daily, house mice drop about 50 or so. Rodent droppings are one of the main contaminants of food stuffs, especially grains.
Runways are frequently travelled routes. Rodents leave greasy fur marks where they repeatedly use the same paths to and from food. These greasy smears persist as marks on beams, pipes, vertical boards where they climb into the lofts of houses, and around gnawed holes they use to go through walls.
Rat and mouse tracks indicate past or present rodent infestation. In dust or mud, the trail of the tail and the 4-toed front feet and the 5-toed rear feet can be seen. Sometimes a fine dust of talc or wheat flour can be laid where rodent presence is suspected.
Burrows are readily seen when terrestrial or fossorial rodents infest a premises. These are usually, but not necessarily, on the outside of the structure.
Burrows are made by Norway rats, bandicoot rats, and sometimes, house mice. In general roof rats, Polynesian rats, multimammate rats, and vesper mice will not make burrows. Burrows are indicated by the soil mounds at their entrances, by the burrow opening itself, and by runways connecting burrows.
All rodents gnaw and gnawed materials in certain instances reveal their presence. The gnaw marks may be seen as actual tooth-marks, as small particles resulting from gnawing, or as round holes around pipes, under doors, through walls, into jute bags, clothing, books, and cardboard boxes.
Nests are found indoors and outdoors in areas offering concealment and access to food sources. They may be found in attics, lofts, between walls, under wooden floors, and in burrows in or near the farm structures. Nests are usually globular or cup-shaped, constructed of soft grasses, leaves, and stems, and sometimes, of cloth or jute fibres from the farm household.
Damage to jute bags, woven bamboo baskets, and other food storage containers is evidence of rodent presence. The damage to bags consists of frayed-looking holes in the sides, bottom, or top of the bagged grain. Grains are usually spilled out and trail away from the bag towards the rodents' burrows or nests. Gnawed holes in the side of the grain basket indicates the presence of rodents in the farm household. Likewise, clothing items, paper materials (books, newspapers, etc.), and bars of soap may be gnawed upon by rodents in the household.
The members of the farm household may sight rodents during the day or night in the farm structures. Sometimes, rodents are disturbed during the daytime. The finding of dead rodents in the farm structures is not conclusive evidence of a current infestation since domestic predators like cats or dogs may have brought them in from outside. Trapping is another means of determining if rodents are present.
The sounds that rodents make will confirm their presence. These sounds are generally made at night when the rodents are foraging for food.