The field mouse and the wood mouse

Unlike the house mouse, field mice live outdoors in summer. They become a problem precisely in autumn, when they look for somewhere warm to see out the winter.

How to recognise them

Larger eyes and ears than a house mouse, a sharper colour difference between the back and the pale belly, and longer hind legs. The striped field mouse has a dark stripe running along its back.

Where they are found

In gardens, greenhouses, sheds, woodpiles, near compost heaps and at the edges of meadows. In autumn they move into garages, basements, summer houses and private homes.

Why autumn is the critical period

When food in the fields runs out and the temperature drops, a building becomes the nearest source of warmth. This is the main reason the number of enquiries rises sharply in September and October.

What to do

The most effective step is protecting the perimeter before the season starts: sealing gaps in the foundations, replacing ventilation grilles and moving woodpiles away from the wall.

Field, wood and striped mice: the practical differences

The three species that end up in houses and outbuildings in Latvia differ from one another in a few clear features. The wood mouse has larger eyes and ears, a sharp boundary between its brownish back and white belly, and long hind legs — it bounds rather than runs. The striped field mouse is smaller and instantly recognisable: a dark stripe runs lengthways down the middle of its back, which no other species has. The house mouse by comparison is a uniform greyish colour with no sharp boundary at the belly, with shorter legs and a stronger smell. In practice what matters is not the name of the species but the conclusion: if the animal caught or spotted has large eyes and ears and a white belly, this is an outdoor species that has come in from the garden or the edge of a field. That means the weight of the treatment shifts to the perimeter and the entry points, rather than the inside of the kitchen.

Why seeds, bulbs and greenhouse plants suffer

These species naturally feed on seeds, grain, nuts, berries and plant parts with a high energy density. That is why the damage on a smallholding is highly characteristic and repeats itself the same way every year. Seed packets in a store or shed are gnawed open at the edge, the contents tipped out and partly carried off to a hiding place. Tulip, daffodil and garlic bulbs are dug out of the bed or gnawed in the storage box, leaving the characteristic fine, parallel incisor cuts. In a greenhouse the newly sown seedlings suffer, along with the remains of apples or tomatoes; the animal cuts the stem off at the base and carries away the seed. Stored carrots, beetroot and potatoes in a basement are gnawed from underneath, where they touch the box. If this damage appears, look not for the animal but for the store: the nest is almost always within a few metres of the food.

Damage patterns in the garden and outbuildings

The presence of outdoor mice is read from the place, not the amount. Under a stack of boards, a tarpaulin or a sheet of plastic that has lain on the ground for a year, you find a network of compacted runs, with tracks about 2–3 cm wide through the grass and several holes about 2 cm across in the soil. In a shed the signs are shredded material in the corner of a box — string, insulation fibres, dry grass — small 3–6 mm droppings along the shelf edge, and fine wood shavings under the bottom of the door. In garden furniture and machinery the polyurethane padding and cable insulation get damaged; a lawnmower or quad bike laid up with its wiring gnawed over the winter is a typical case. Write down exactly where the damage was found and give this information on the form — it lets us plan the points along the real route rather than to a standard scheme.

Why they are more seasonal than house mice

The house mouse is closely tied to human buildings and can live in one all year round, whatever the weather. Outdoor species live differently: their main home is the field edge, the woodland margin, scrub, ditch banks and the untended part of the garden, and a building is a seasonal refuge for them. The main wave of arrivals is short and predictable — from the end of September until the first settled frosts, when food outdoors runs out and the nights turn cold. In spring some of the animals go back outside of their own accord. That is why the problem often looks like an unexpected invasion: no signs at all in summer, and then suddenly, within two weeks in October, tracks all over the shed. The practical conclusion is simple: preventive treatment and sealing entry points in September avoids what would otherwise have to be dealt with in November as a fully formed problem.

How to protect a greenhouse and a woodpile

In a greenhouse the crucial thing is the bottom edge. There is almost always a 2–5 cm gap left between the base and the ground at the bottom of a polycarbonate or glass structure, and this is the main entry point; the answer is metal mesh with an aperture of up to 5 mm dug in along the perimeter, turned outwards at a depth of about 20 cm. Inside, seeds and planting material must not be left overnight in a cardboard or plastic bag — only in a metal or thick plastic container with a lid. The woodpile is the second problem: firewood stacked on the ground right against the wall makes an ideal nesting site, with warmth, dryness and complete cover. Stack it on bearers at least 30 cm off the ground and at least a metre away from the building wall, with free access from every side. That one rearrangement often reduces the influx into the building more than any other measure in the garden.

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