A single female rat can have up to 6 litters a year. Each litter may contain up to 8 young and they are soon mature enough to start reproducing themselves. Rats are very good climbers, and they continuously chew to keep their teeth short so they can feed. Without the chewing their two front teeth can grow to 4 inches in a year. A single female mouse can produce up to 8 litters per year with up to 8/9 new born in a litter. They are mature and can start producing their own from 6 weeks old. Each mouse will average 80 droppings per day. Rats and mice are disease carriers and can cause substantial structural damage and contamination.