Rodents in the Garden

Gardens can provide a safe harbour for several types of rodents, giving shelter and readily-available food sources both growing in the garden and stored in sheds or garages. Rodents are not wanted in your garden because of the damage they can cause to fruit, vegetables, seeds, bulbs, plants and containers, and also because they expose people and pets to various diseases and parasites.

The rat species you are most likely to find in your garden is the brown or Norway rat (Rattus norvegicus). The black rat is more likely to be found near coastal areas and ports.

There are several mouse and vole species native throughout the UK, and a small number of these can take advantage of food and lodging opportunities provided in gardens. However, their numbers are rarely high enough to cause much damage in the garden.

The house mouse (Mus musculus), wood mouse (Apodemus sylvaticus), field vole or short-tailed vole (Microtus agrestis), bank vole (Myodes glareolus — sometimes still referred to by its old name Clethrionomys glareolus), and yellow-necked field mouse (Apodemus flavicollis), are species most likely to be seen frequenting gardens.

These rural species are normally found in specific habitats:

• Wood mouse: woodland, hedgerows, occasionally indoors;
• Bank vole: woodland, hedgerows, earth banks;
• Field vole: rough grassland;
• Yellow-necked field mouse: broadleaved woodland, hedges, rural gardens;
• Common vole: meadows, heathland, agricultural fields.

Start by look for nesting areas - under rubbish, timber or wood piles, in drain pipes, underneath and in sheds, out houses or garages. Rodents have a characteristic smell when in large numbers and you may also hear their activity. They are usually nocturnal feeders, so you will not normally see them in the daytime. If you do see them it usually means they are short of food and desperately searching for new food sources.

• Holes or burrows: burrows are about 6-9 cm in diameter and can be located anywhere that is relatively undisturbed and near to food.
• Runs and tracks: runs are typically 5-10 cm wide near cover along walls, banks and hedges and through vegetation. Rats memorise pathways and use the same routes to and from their shelter. Smear marks may be visible where they run along stone, wood or metal, such as on steps, fencing and gate posts. They tend to travel along the ground, but they can climb and jump to get to food and shelter.
• Droppings: these are approximately 15-20 mm long, cylindrical, flat at one end and often pointed at the other. They are moist when fresh, but dry within hours.
• Damage: rats will gnaw at food, packaging and barriers in their way, making holes or enlarging existing ones. They also gnaw objects when investigating them. Their teeth are hard enough to get through many hard materials such as wood, rubber, vinyl and low grade concrete and cement. Outdoors this can be fencing panels, sheds where food is stored, compost bins and electrical wiring in sheds, such as on power tools.

• They construct a system of tunnels to live in, which can have several chambers and exits. Voles can make a system of shallow tunnels that give a soft and uneven surface to lawns and soils.
• Small gnaw marks can be seen on fruits such as growing strawberries and stored apples and seeds. Small fruit, such as berries may be left scattered on the ground under the plants.
• Torn paper in garden sheds shows mice are gathering nesting material.

Rodents can cause an array of damage in your garden which can range anywhere from feasting on fruits and vegetables to gnawing on shed doors and wires. The type of damage that may be caused will vary depending on the species of rodent involved.

• Eat a wide range of garden vegetables, including various root vegetables, such as carrot, parsnip, beetroot and potato tubers. They will eat the crops while they are growing and any they find stored in garages or sheds. They also eat fruits in storage such as apples, and seeds.
• Eat feed put out for wild birds, poultry and pets, so this needs to be on bird tables or in hanging feeders, not on the ground and cleared away daily at dusk, along with any spillage's.
• Damage containers and packaging materials in which foods, animal feed and seeds are stored.
• Cause structural damage to buildings by burrowing and gnawing, undermining building foundations, paving in patios and paths, causing settling, and damage earth banks.
• Gnaw on electrical wires or water pipes, above or below ground.
• Rats are opportunistic, so once they are in your garden they will seek new places to live, feed and breed, such as in your house, so it is important to control them as soon as possible. You may only see one or two, but there will be many more that you don’t see! They can damage buildings further by gnawing openings through doors, window sills, walls, ceilings, and floors to gain access.

Mice and voles will feed on a wide range of plants, but do relatively little other damage in the garden:

• Eat recently sown vegetable seeds such as peas, beans and sweet corn and the foliage of seedlings.
• Eat bulbs and corms, especially recently sown ones. Tell-tale signs are holes in the soil where they have dug down to feed on them.
• Eat fruits such as strawberries, even before they are ripe and berries.
• Eat stored fruit such as apples.
• Voles can eat the bark of woody plants, especially in winter.
• Voles make a network of shallow tunnels which can give lawns an uneven surface.

Rats, mice and voles can carry a wide range of rodent-borne diseases caused by bacteria, viruses and helminths (worms), including Salmonella, Leptospirosis, Weil’s disease, Cryptosporidium and rat bite fever. They can infect both people and pets. They can also carry ectoparasites such as ticks, mites, fleas and lice that carry another set of diseases, and can pass them on to others.

In the garden, contamination from rodents may not be as obvious as in the home, but there are several means of disease transmission, which include:

• direct contact with excreta (urine, faeces, saliva) or inhalation of dust particles;
• handling or inhaling dust particles containing infectious microorganisms aerosolized when disturbing compost heaps, woodpiles, or other material contaminated with dried rodent urine;
• handling of infected rodents, alive or dead;
• scratches or bites from rodents;
• dogs, cats catching/eating rodents gives parasites the opportunity to cross infect pets and people.

Rodents need food and shelter to live, so if you can take steps to deny them both of these you can reduce the chance of them invading your garden.

• Eliminate any harbourage points around buildings and sheds. Seal any small gaps that allow them access. Rats need only a gap height of around 15mm to gain entry and mice 6mm, though normally mice access holes are 20-20mm in diameter.
• Remove potential nesting places by keeping gardens clean and tidy. Remove piles of wood, garden clippings etc, cut back overgrown areas, and keep lawns short.
• Cover any household food waste such as in compost heaps and dustbins. Make sure bin lids are tightly fitted and rubbish bags containing food are not left outside for long periods.
• Do not scatter bird feed on the ground: use a bird table or feeder basket to feed birds and clear away before dusk.

Wood mice, yellow-necked field mice and voles rarely build up in large enough populations in gardens to become serious pests, so it is usually not necessary to control them.

There are however, a number of DIY rodent control products available for the home use to help eliminate rats and mice.These will need a degree of skill and care to use effectively and safely. You should only use products that are designed for the ‘target’ pest animal and use methods that are considered safe for other people, pets, wild animals and the environment. You should read the description and instructions on DIY product packaging very carefully before use.

If you are concerned that rats are nesting in your garden or that rodents have entered your property, the safe and secure option is to call a professional pest controller, who will be trained, qualified and have the knowledge and expertise to assess your rodent problem and deal with your infestation effectively.

Use biocides safely. Always read the label and product information before use.