House mice living indoors are usually a darkish grey colour, with lighter grey on the belly, while those living mainly outdoors tend to a more sandy or yellow-brown colouring. The house mouse has an even higher reproductive potential that the norway rat and roof rat because they reach their sexual maturity much earlier at only 6 weeks of age.
The house mouse may live indoors or outdoors, sometimes entering buildings only when climatic conditions are adverse. Being such small animals, their ease of access to buildings and the range of possible nesting sites is much greater than that of rats. Typically within buildings they may nest in wall voids, cupboards, roof voids, stored foods, furniture and many other locations. Outdoors they live in burrows.
House mice are very good climbers, jumpers and swimmers, although they do not seem to swim very often. In terms of their feeding habits, mice are generally regarded as being quite omnivorous. They consume a variety of foods including nuts, grains, fruits, meat meals and animal feeds. The best food to use on baits and traps may vary though depending on the main diet of the resident population. Mice are well adapted to low water intake and can live on just the moisture in grain without any supplementary intake of water. Preferably, though, they seem to enjoy dry cereals if free water is available. Mixing certain baits with water can make them very attractive. Mice feed mostly around dusk and during the night, but if the area is relatively undisturbed, they may feed during the day as well. They seem to prefer to eat small amounts of food at various locations and at frequent intervals. Even though they do not directly consume large amounts of food, damage due to gnawing, nibbling and contamination with urine and faeces can be widespread.
In rural areas the occasional combination of mild weather, abundant food and shelter, and a reduction of natural enemies may cause mice to multiply to plague proportions, and then to migrate. Massive migrations can cause very significant damage and losses to farms and other buildings.
In their general behaviour, mice are much more curious and exploratory than rats, so trapping programs for mouse control can often be very effective as mice are not as suspicious of new food sources, such as baits, the way rats are.
If you don’t think it’s house mice you are noticing the second largest rodent is the Roof Rat.