The House Mouse Mus domesticus is the typical mouse of human habitation. After the last glaciation it was found in the Middle East, associated with the earliest agricultural settlements. It spread through the Mediterranean arriving in Western Europe during the Bronze Age and had reached Britain by the Iron Age (Harris and Yalden, 2008). In this region it has been recorded from the late 3rd or early 4th century from a Roman granary in South Shields, where it formed 30% of the total number of small mammals recovered (Younger, 1994).
It is a small (10-20 g) animal with a generally dull grey-brown colouration, the back being darker than the underside. However as it is the ancestor of all our domestic mice (which come in a variety of colours), due to escapees there is probably a wide range of genetic material in the population and as a result a range of colours is possible.
The eyes are bright and ears large but neither as noticeable as in the Wood Mouse Apodemus sylvaticus. The tail is approximately the same length as the body and slightly thicker and more scaly than the Wood Mouse and less likely to shed the skin when handled. House Mice can breed throughout the year, except when living outside when they do not breed during the winter. Litters are of five to eight young which are sometimes reared communally with two or more females sharing a nest. In ideal conditions 10 or more litters can be raised in a year. The young can breed themselves at six weeks.
The natural habitat is thought to be rock crevasses but in Britain it is mainly found around buildings. It will extend into gardens and hedgerows but in competition with Wood Mice will probably not prosper. Competition with Wood Mice is believed to have led to the extinction of House Mice on St Kilda after the human population left the island (Harris and Yalden, 2008). On the Isle of May in southeast Scotland, where Wood Mice are not found, House Mice live away from buildings in cracks in the cliffs and in stone walls as they do on Skokholm Island off southwest Wales. Individuals of both of these island populations are 15% larger than on the mainland but are genetically different from each other (Flowerdew, 1993).
Though modern farming practices and domestic appliances have somewhat reduced the habitat, it is still a pest in farm buildings where its major competitor and predator is thought to be the Brown Rat Rattus norvegicus. Modern methods of pest control involve laying poison and maintaining it until all signs of infestation have ceased. The operator need never see the cause and species responsible. A side effect of this is that strains of poison-resistant rats and mice have developed and are difficult to eradicate. A second effect is that whatever is causing the infestation is not seen and not identified so no record is available. The National Pest Technician Association’s 2010/11 Rodent Survey recorded a 2%, like for like, increase in mouse infestations from 2009/10 to 2010/11 with both figures being similar to that for 2001/02 (NPTA, 2012). The survey is based purely on Local Authority pest control services, and given the marked increase in the number of Local Authorities charging for such services in recent years, it would seem to suggest a significant increase in mice infestations.
However, while the House Mouse is described as the mouse of buildings, it cannot be assumed that all mice found in buildings are House Mice. Indeed where mice are found in domestic garages and garden sheds, particularly in winter, they are very often found to be Wood Mice (Derek Abbey, pers. comm., 2011). This also applies to farm buildings, for example hay barns, which can also host Wood Mice and even Harvest Mice Micromys minutus.
One characteristic of common animals is that they become so familiar that they are ignored and as a result are not recorded. For example our distribution maps show them as the only widespread small mammal not present on Lindisfarne, though they are known to be present there (Andrew Craggs, pers. comm., 2012). This has happened to such an extent with the House Mouse that in the years before the turn of the present century only one record was held on the Environmental Records Information Centre database. This was in Cleveland in 1977 at Lovell Hill Ponds in the extreme southeast of the region. Similarly, Arnold (1993) records them in less than 20 hectads throughout the region. There has been no improvement since then and large areas of the North East, particularly in the western uplands, have no records, though it is extremely unlikely that the mice are absent. The recent records are mainly concentrated around the large areas of human population in the east, suggesting that they are more a record of interested observers than of the mice themselves.
Historically, authors have tended to make little mention of the small mammals, their interest being more towards beasts of the chase and the larger predators. In his list of fauna in The History and Antiquities of the Parish of Darlington published in 1854 (republished in 1973 by Patrick and Shotton), W.H.D. Longstaffe mentions “the usual rats and mice”. He does however list Common Shrew Sorex araneus and Water Shrew Neomys fodiens. The Victoria History of the County of Durham (Page, 1905) has a section on the mammals by E.L. Gill who goes no further than saying “Very common about habitations everywhere”.
Written by Don Griss (last updated Nov 12)