The harvest mouse is the smallest rodent in Britain weighing just 6 grams, about the same as a twenty pence coin, its scientific name, Micromys minutus, reflects its tiny size but it wasn't given a common name until the 18th century for the simple reason that it hadn’t been discovered until then. It was called the harvest mouse because it was only commonly seen when crops were harvested and the mice disturbed.
The harvest mouse doesn’t live entirely in arable fields, in fact such habitats have always been temporary so harvest mice have always lived around field edges and only moved into the crops during the summer period. Nowadays arable crops are much less suitable than they once were because our intensive farming techniques mean that crops grow more quickly and have less insect life amongst them. As a result hedgerows, patches of reeds, rough grassland and wildflower meadows are more important.
Gardens can also be valuable habitats for harvest mice, particularly where they contain some wilder areas and link up with hedgerows leading into the countryside. In fact my first sighting of a harvest mouse in the wild was in my garden shed. I always have dustbins full of bird seed in my shed and sometimes I lift the lid to find a mouse within. Usually it is wood mice which take advantage of this bounty but once a harvest mouse had dropped in.
One feature, other than its small size which makes the harvest mouse truly unique amongst British mammals is its tail. The harvest mouse has a tail about as long as its own body which can be used to hold onto things just like a monkey does. This prehensile tail is useful to the mouse when climbing amongst the stems of corn and grass in a field enabling it to maintain its balance and spread its weight.
Harvest mice don't live long, probably only up to 18 months, but they do reproduce quickly. Their breeding season begins in May and sometimes lasts until December. They can raise up to seven litters during that time, each consisting of up to eight young. One of the best ways of spotting the presence of harvest mice is to look for their nests.
The nest of a harvest mouse is a beautiful structure of interwoven grass leaves, usually created some 50cm off the ground and about the size of a tennis ball. It is made by pulling leaves of adjacent grasses together, shredding them along their lengths and weaving them together to form a spherical nest suspended between the grass stems. In this way the grass which forms its nest continues to live so it will remain green and provide ideal camouflage. If its nest should turn brown then it will be abandoned.