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Brown Rat - Fact File

Size: 19-28cm (head+body length).Tail 60% body length. 100-500g (average about 350g).
Markings: Grey/Brown or black fur, slightly lighter undersides.
Location: Just about anywhere that man is found, and more.
Detection: Customer will report live sightings, scuffling noises, droppings and gnawed goods, smell. Nesting materials sometimes seen

Britain is host to two species of rat, Rattus norvegicus (the Brown or sewer rat) and Rattus rattus (the Black or ship rat).

The Brown Rat is the newcomer to our shores, arriving several hundred years ago from Asia. Weighing 100 - 500 grammes, its upperparts are dark brown becoming lighter brown to grey or even white on the underparts. The tail is shorter than the head and body and the head and face are quite blunt in appearance.

The Black rat is far less common and restricted to only 3 major ports. Its appearance is sleeker with a body weight between 100.300 grammes with brown to black fur, large almost hairless ears and a tail which is longer than its head and body. This enables it to be very agile and an excellent climber which gives rise to its other name "Roof Rat".

Biology:

Important details of rat biology and behaviour are summarised below.

The life expectancy of a wild brown rat is approximately 10-14 months in which time the female will typically breed between 5 and 7 times, with an average litter size of between 7 and 8 young. Breeding can occur throughout the year depending more on the availability of food and harbourage than on weather conditions. Around 800 offspring from one pair or rats is possible, under ideal conditions. Both species are most active at night but may be seen in search of food and water during daylight hours.

Immense damage can be caused by rats feeding in warehouses, factories, shops and homes due to both quantities of food consumed, contamination by faeces and urine, and damage by gnawing. Contamination and possible introduction of microorganisms which can cause food poisoning, such as Salmonella make this rodent a major public health pest. Remember rats carry Weil's Disease (Leptospirosis) which can cause serious illness.

Many signs of infestation may occur, droppings being the first possible sign followed by gnawing. Damage to fabrics, excavations around or under buildings, well worn runs through undergrowth or smear marks (a dark mark caused by body grease) over surfaces which are crossed regularly are other tell tale signs. Where infestations occur near water courses holes will often be present in the banks as this offers an excellent escape route as rats are accomplished swimmers.

Rats have five senses like humans, with particularly well developed hearing, smell and touch, but they are colour blind. They do have good movement detection.

Treatment:

Thorough inspection of the building will enable you to determine the extent of the infestation, by looking for signs of their presence. These include the characteristic 'musty' smell, sightings, dropping, hairs, runs, and smears. As with all infestations, time spent assessing this information during the initial survey and subsequent treatment is essential in gaining control of an infestation.

1. Baits. When feeding, rats can exhibit neophobia (new object reaction) - this means that although a bait is palatable to them, it may not be touched for several days until they get used to the new object in their environment. When planning a baiting programme, it is important to consider what foods the rats are currently eating, and where. Scrupulous hygiene is vital as other food sources will impede successful treatments.

Modern rodenticides tend to be single-feed-kill anticoagulants which affect the clotting of the blood and cause death by blood loss. Their action is quite slow, taking from 3-10 days. The antidote for anticoagulants is Vitamin K1 (Phytomenadione). Bait bases can include block, or soft wax, but a loose grain bait base is particularly good. Consult your pesticide supplier for advice if you are having problems with bait palatability.

New gels are also useful in areas where the rats run on a regular basis, as they can be eaten or ingested by grooming.

Baits should be placed in trays or boxes along runs or behind fixtures. Tamper-resistant bait boxes may be necessary when there is a risk of non-target species gaining access to the bait points. A COSHH assessment should be carried out to ensure safe use and placement of baits. Bait points should be inspected at least weekly, replenished where necessary, and removed after a successful result has been achieved.

2. Liquid Baits. These are excellent for rats, especially if there is an abundance of other foodstuffs or the environment is particularly dry, as they must drink daily. Liquid rodenticides are anticoagulents that are diluted with water, placed in liquid feeders and treated in a manner similar to baits.

3. Dusts. Dust formulations containing rodenticides are useful in runs that can be identified or in voids / cavities that are thought to harbour rats. The dust adheres to the rat's fur and is ingested by grooming. This method is useful as it does not require the rats to feed, but care should be taken as the dust can get easily blown or trodden on sensitive areas such as food preparation surfaces.

4. Traps. Traps are still an excellent method of rat control. Bait with apple, bacon rind or chocolate and place at 90° to the wall. Live traps are also good, but must be visited daily. Glueboards should be considered as a very last resort, as their use is strictly monitored.

5. Proofing. Exclusion should always be the primary methods of control. All gaps greater than 11 mm must be sealed using mortar, mesh or brushstrip.

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