Rats

Rats are very common animals, they can damage growing and stored fruits and vegetables, they can also spread some potentially serious diseases.

Rat damage on carrots

Rat damage on carrots

Quick facts

Common  name Brown rat
Scientific name Rattus norvegicus
Plants affected Vegetables, especially root crops, sweet corn and stored fruits
Main cause Rats eating growing and stored crops
Timing All year round

What are rats?

Rats are rodents that are widely distributed and common in Britain. They occur in the countryside and can be very common near human habitation. They are highly adaptable and feed on a wide variety of foods. They make their homes underground or in compost heaps, in buildings, greenhouses, sheds or drains. Backyard poultry keepers frequently encounter rats as they often take advantage of poultry feedstuffs.

Appearance

Rats can eat sweet corn cobs, pumpkins and squash and various root vegetables, such as carrot, parsnip, beetroot and potato tubers. Damage can occur while the crops are growing and when they are being stored. Harvested fruits, such as apples, can be similarly damaged. Seeds can also be consumed.

Parallel grooves, where a rat's incisor teeth have bitten into the food material, are usually visible. Rat tunnels in the soil have an entrance diameter of 30-40mm. Rat droppings may be visible where damage has occurred. The pellets are cylindrical in shape with rounded ends and are about 15mm long and 5mm wide when fresh. Adult rats are about 21cm long with relatively hairless tails that add another 18cm to the animal's length.

The problem

Rats cause damage to foods that we intend to eat, either while it is growing or after it has been harvested and is being stored. Rats will take food provided for wild birds, poultry and pets. Rats are often infected with a bacterial disease that can also infect people, causing a form of jaundice known as leptospirosis or Weil's (pronounced 'Viles') disease (NHS information). The bacterium is spread in rats' urine and can persist in wet places. It infects people through cuts and abrasions or by ingestion. The risks can be minimised by taking some simple precautions listed here.

Rats have a liking for compost heaps, the light friable nature of the compost is ideal for burrowing. Compost that has come from a rat-infested bin or heap can be used in the garden but do not use it for fruits or vegetables that are going to be eaten raw and the edible parts may be in contact with the soil or compost e.g. radish, celery, cucumber, strawberry.

Control


Discourage rats by removing any accessible food sources, for example by making sure bins are sealed. When feeding wildlife such as birds, do not let access food build up (this will also help reduce the risk of spreading wildlife diseases). Removing clutter will reduce hiding and nesting places for these animals. More information on living with rats can be found in the RSPCA living with series.

When control of rats is necessary pest control contractors can be employed to deal with rat infestations, or they can be controlled with traps or poison baits. Many local councils offer a rat control service. In urban areas rat control over an area larger than one garden is often required to keep rat numbers in check.

Break-back rat traps, similar to the traditional mouse trap, can be set in places where rats are active, these can be baited with a wide range of foodstuffs for example bread, cereal or chocolate.  They must be placed so that other animals do not have access to them.

Several types of poison bait are widely available. Only baits approved for outdoor use can be used in gardens, and every care (by closely following the manufacturer's instructions) must be taken to avoid non-target species consuming the bait. Baits approved for indoor use can be used in sheds, greenhouses and other outbuildings, but again great care must be taken. Accidental poisoning of non-target animals is illegal. Bait should continue to be put down until rats stop taking it as it often requires several meals before the rats are killed.

Dead animals should be disposed of by burying them or placing the corpses in a polythene bag in the dustbin.  Always wear rubber gloves when handling traps or dead rats. 

Biology

Rats can breed at a prolific rate, with females having up to five litters a year. The average litter has seven young but as many as 14 have been recorded. 


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