While field mice are widespread on Hirta, their concentration is more pronounced in the old village areas where holes provide access into buildings.

[2] The mouse has black eyes, small peaked ears, and is fairly uniform in colour: mainly brown, with a lighter shade of fur on its underside.

[6] Studies of the fur of the mice have recorded the flea species Ctenophthalmus nobilis, and Nosopsyllus fasciatus on the mouse as well as the mite Typhloceras poppei.

[5] With only one other naturalised mammal, the Soay sheep, which eats grasses and herbs, the St Kilda field mouse faces little competition for food on the islands.

[8] Unique to the islands, the ancestors of the St Kilda's field mouse are believed to have arrived on the ships of Viking settlers.