This contamination is often difficult to remove and leads to the rejection of food for human consumption. Rats and mice often destroy much more than they consume because of their wasteful habit of discarding partially eaten food.

They also cause structural damage by gnawing and burrowing. In particular they undermine foundations and destroy the fabric of the building. Structural drain sewers can be damaged by burrowing between joints in the surrounding earth and behind brick sewers. Sometimes this causes or contributes to the collapse of roads and pavements. Almost any commodity is susceptible to gnawing. Lead pipes and even metal sheathed cables can be gnawed through. Rats frequently attack electrical wiring, resulting in electrical failures and fires. The presence of rodents in buildings is highly undesirable. The rat most commonly found in Britain is the Brown Rat (Rattus norvegicus). The Black Rat (Rattus rattus) is only likely to found in or near Ports.