The Brown Rat is the larger of the rats in Britain, often weighing over half a kilo and measuring about 23cm, without counting the tail. It has a blunt muzzle, small hair-covered ears and a tail that is shorter than its body. The Black Rat weighs half as much and is shorter. It has a pointed muzzle, large, almost hairless ears, a more slender body and a long thin tail that is longer than its body.
Rats have well developed senses of smell taste and touch. They have an acute sense of hearing, frequently using ultrasound to communicate, and are particularly sensitive to any sudden noise. Both species breed rapidly and become sexually mature in about three months. Each female may produce from 3 to 12 litters of between six and eight young in a year. Rats need to gnaw to keep their constantly growing incisor teeth worn down. They damage woodwork, plastic, bricks and lead pipes, and will strip insulation from electrical cables.
Brown Rats live in any situation that provides food, water and shelter. In homes, they will live in roof spaces, wall cavities or under floorboards. In gardens, they will burrow into grassy banks or under sheds. Brown Rats are often found living in sewer systems. Black Rats are rare and are occasionally found in shipping ports.
The House Mouse body length ranges between 60-90mm and the tail can add an additional 100mm. They weigh less than 25g, and their fur colour varies between light brown and grey.
Mice have an acute sense of hearing, frequently using ultrasound to communicate, and are particularly sensitive to any sudden noise. Their presence is usually detected from their dark-coloured droppings or damage to stored foods in the larder, packaging or woodwork.
Mice live in nests that they build out of cloth, wool and paper. Nests are often built inside houses, in places such as roof spaces, under floors or in wall cavities, and wherever there is access to a good source of food, especially during the winter. Mice can squeeze through cracks as small as 5mm but mouse holes are normally 20-30mm in diameter. Mice are mainly active at night and can often be heard running about as they search for food.