Pest control of rats and mice

Information about rats and mice


The adult rat weighs 100 to 500 grams, measures about 24cm long (excluding tail) and is brown/black with grey fur underneath. Its tail is shorter than the head and body together. 

Rats are efficient burrowers and favour compost heaps and the ground underneath hedges and sheds, where they will dig shallow burrows and form nests with dry grass and leaves - in houses they nest in wall cavities and beneath floorboards. 

They are good climbers and can climb vertical brick walls. They are also proficient swimmers and are at home in sewers where they have food, water and shelter. 

The front teeth of rats grow continuously and they gnaw on hard objects such as lead water pipes, brickwork, electric cables, wood etc. to keep them at a manageable length. 

Rats are usually active at night, but may also be seen during the day. 

They usually have well worn runs between their living area and source of food and water. 

The life expectancy of a rat is approximately one year, during which time a female will typically breed five times with an average litter of 8. Female rats will have their first litter at the age of 4 months. 

Rats can be a major hazard to health as they can spread many forms of disease (especially through droppings and urine). Some of these diseases, such as leptospirosis, can be fatal to humans although incidences are rare. 

They may eat food which is intended for human consumption and their gnawing can cause structural damage to woodwork, water pipes, electric cables etc. 

Rat infestation can be characterised by the following signs: 

  • Damage caused by gnawing - packaging will often show tooth marks which will indicate whether it is a rat or a mouse 
  • Holes made by rats in doors and walls, and the entrances to nests, are about 80mm (3inches) in diameter, and nests may be made in wall and floor cavities 
  • Rat runs: once the best route has been established, rats tend to use this run frequently and it will become soiled with the grease and dirt and be very apparent in even moderate infestations 
  • Smears and droppings: a good indication of the size of infestation and how long it has been there 
  • Footprints can be seen on soft or dusty surfaces 


An adult house mouse weighs 30 grams and is 90 mm long (excluding tail). It has brown fur with grey stomach and large ears (in relation to the body) and small feet. The tail is approximately the same length as the head and body. 

Mice can be confused with young rats which have smaller ears, larger feet and thick tails which are shorter than their body. They are widely distributed throughout urban areas and in farm buildings. 

The house mouse is the most common domestic pest and will nest in partitions, floors, and behind wall boarding. Mice are mainly active at night and occasionally during the day. Mice are excellent climbers and can scale vertical brick walls. They are not dependent on having a source of water and obtain sufficient moisture from food. 

The life expectancy of a mouse is a year. Females may breed up to six times (with an average litter of six) and start producing babies at 2 months. 

Mice are a hazard to health and can be responsible for the spread of disease. They may eat food intended for human consumption and contaminate with urine, droppings and fur. All contaminated food should be disposed of. Mice can also cause structural damage by gnawing woodwork, water pipes, electric cables and household items. 

Signs of mouse infestation include damage caused by gnawing, feeding holes, smears and droppings. Mice nibble from the centre of a grain, whilst rats often leave half grains or pieces of debris. Nest entrance holes are about 20mm diameter and appear in the ground, floors, walls and the base of doors. Footprints may be evident in dusty environments. The amount of droppings present indicates the size of infestation and how long it has been there.