The most common rat infesting homes is the Norway Rat. They typically live about one year, but in some cases may survive longer. Female rats may have up to seven litters of young per year. Rats don't hibernate. Winter nights can mean a rat in a house. Rats are most common in roof spaces, cellars and cupboards. They can also live in the walls. Rats leave tooth marks - they gnaw through soft metals, such as lead and aluminum. Chewing wiring is a the biggest problem caused by both rats and squirrel in the winter – it can lead to house fires. Rats can destroy or contaminate food supplies. Their feces and urine are a source of gastrointestinal diseases such as Salmonellosis and E-coli infections. They also cause respiratory diseases such as Hantavirus.