The rat normally found in rural and urban locations is the common or brown rat, Rattus norvegicus. This rat can carry a wide range of diseases and parasites that are potentially harmful to both humans and livestock. In addition, rats can cause damage to buildings and property, as well as eating and contaminating stored foodstuffs.

Rats live in colonies and have the breeding capability to increase rapidly their numbers. An adult female rat can produce an average litter of seven or eight young every three or four weeks. Rats live in burrows or within the fabric of buildings and other structures, and they rely on the availability of suitable harbourage, food and water in order to thrive. Rats are capable of exploiting a wide range of different habitats and situations.

Their gnawing behaviour results in damage, they are good climbers and are capable of swimming.

Of the diseases carried by rats in the United Kingdom, the potentially fatal Leptospirosis or Weils Disease is the most well known, with some 15-30% of rats likely to be carriers. As a result, infested areas should be considered a source of this disease. The bacteria are excreted in rat urine and are passed on when humans come into contact with contaminated surfaces.

The direct and indirect costs of structural damage by rats can also be high. Containers, packaging, insulation and many other materials are vulnerable to their gnawing activities. There is a significant risk of fire and electrocution as a result of damage to electrical cables and wiring.