Mus musculus Linnaeus, 1758

The house mouse (Mus musculus) probably has a world distribution more extensive than any mammal apart from humans. Its geographic spread has been facilitated by its commensal relationship with humans which extends back at least 8,000 years. They do considerable damage by destroying crops and consuming and/or contaminating food supplies intended for human consumption. They are prolific breeders, sometimes errupting and reaching plague proportions. They have also been implicated in the extinction of indigenous species in ecosytems they have invaded and colonised which are outside their natural range. An important factor in the success of the house mouse is their behavioural plasticity brought about by the decoupling of genetics and behaviour. This enables the house mouse to adapt quickly and to survive and prosper in new environments.

Mus musculus was originally a Palaearctic species, but through its close association with humans it has been widely introduced across the globe (Musser and Carleton, 2005). The species is widespread over all continents, except Antarctica, and has become established in North and South America, sub-Saharan Africa, Australia, and many oceanic islands (Macholán 1999). The list of countries of occurrence is incomplete.

The house mouse is one of the most widely distributed and successful mammals in the world (2). It has dull greyish-brown fur and the tail, which is the same length as the body, is thicker and scalier than that of other species of mice (3). It is accompanied by a distinctive strong 'stale' odour and its presence can easily be detected by means of its droppings (2). Forms of this species living in association with man ('commensal' forms) tend to be larger and darker than 'wild' forms, and have longer tails (3). The voice is a familiar high-pitched 'squeak' (3).

It is thought that the house mouse originated on the steppes of central Asia and possibly the Mediterranean area. It is now found around the world as a result of introduction by humans. It is known that the species has been present in Britain since at least the Iron Age, as remains have been found in deposits dating from this period. At present, the species is found throughout Britain and Ireland where there are human settlements (3).