Norway Rat (Rattus norvegicus).

This species arrived in this country in around the 1720's and has largely replaced the black rat. Its habitat is mainly outdoors except on intensive livestock units. It is a burrowing rodent being mostly nocturnal and feeds at 2-3 familiar points each night. Each rat can produce 15,000 droppings and 5 litres of urine annually and gives birth to 5 litters/year each litter numbering 8-9 young.

The Black Rat (Rattus rattus).

Numbers of Black Rat have dwindled over recent years and they now only occur in a few areas. They are smaller than the Norway rat, have thinner tails, large eyes and pointed snouts.

Rat facts:

• Rats prefer living close to watercourses
• Individuals can move 3km or more in one night
• Rats sample novel food
• Rats are more wary of containers than the food inside
• Black rats leave loop smears near beams
• Norway rats leave smears same size but continuous
• Rat droppings are 20mm long and 7mm wide
• Norway rats deposit droppings in groups
• Black rat droppings are more scattered
• Rats like to nest near cover
  

House Mouse (Mus domesticus/musculus).

This is very common and found in many buildings and lives in a social group of 4-9 dominated by a single male. It feeds at about 20 points each night and does not require free water as it can utilise moisture in feed. Each mouse can produce 30,000 droppings per year and 0.75 litres urine.

House Mouse facts:

• Breed all year round and litters at monthly intervals
• Average 5-6 per litter
• Originates from arid areas
• Favours tunnels found in structure of buildings
• Mouse burrows are 2-3 cms in diameter
• Can squeeze through gaps a small as 1 cm
• Proofing requires no gap >6mm
• Mice feed erratically visiting many points
• Change main food source each night
• Mouse droppings 6mm long by 3mm wide
  

Diseases carried by rats and mice:
Leptospirosis
Salmonellosis
Cryptosporidiosis
Viral Haemorrhagic Fever (USA)

Why do we need to control this pest?
Rodents not only eat and damage significant amounts of food and foodstuffs each year but they also contaminate stored products with faeces and urine. This in turn may transmit disease to humans and livestock. Indirect transmission of disease may be through contaminated mud, dust and parasites carried on feet or fur. It can be seen from this that good hygiene is important to reduce the threats to the health of livestock and humans caused by rodents.
Apart from spreading disease, rats and mice can cause physical damage to some crops. With their tremendous ability to gnaw they can also cause serious damage to buildings and internal fixtures. It is not unknown for them to gnaw through wires and even pipes.

Strategy for control.
To reduce the population of rodents it necessary to monitor activity all year round and implement cleaning procedures to eliminate food sources. This must be combined with a policy of hygiene management and proofing. Make the environment an inhospitable area to rodents. (Clear and tidy areas where rats can inhabit). This is a chance to tidy up the immediate area around the farm and buildings and eliminate those areas where rats and mice are likely to thrive.

Rodenticides.
Chronic (multi -dose). These are anticoagulants and the most commonly used poisons. They cause death by haemorrhage. Effectiveness depends on regular and continuous feeding. Death occurs 14 days after feeding commences. If regular feeding is not maintained then recovery may occur. As this is a slow acting poison, shyness and reluctance to feed is not induced. There are first and second-generation products covering this group. Second generation products where introduced to overcome resistance. Check and replenish bait points at least once a week.

Brodifacoum and Flocoumafen are licensed for indoor use.

Sub-acute.
The only chemical in this category is calciferol (vitamin D3). It takes two to three days to ingest a lethal dose and death occurs within 48 hours. Death is by kidney failure. Use fresh bait, apply at high density (1 bait point/sqm) and check bait once a week.

Acute (single dose).
These products are fast acting. Unless a lethal dose is consumed during the first feed rodents may shy away from it. Mortality is only in the region of 70-80%.
Zinc phosphate - kills Norway Rats (affects the nervous system). Pre bait with unpoisoned bait for at least a week. Poison the same bait base as was used for pre-baiting and apply poison for 3 days.
Alphachloralose -kills mice (causes hypothermia). Do not use above 14degrees C, remove all alternative food and place small bait points at very high density (1/sqm).
Alphacellulose-based products are new to the UK market and are presently being considered by the regulatory authorities.

Rodenticide formulations.
These are many and varied.
Loose baits based on cereals are the most widely used and most effective. Many contain Bitrex a human taste deterrent to increase safety.

Loose cereal baits. Can be bought in this form or made by mixing Rodenticide concentrates with readily available food sources from off the farm. They are also available in sachet packs.

Edible gels. Can be applied using a caulking gun.

Wax blocks. More weather resistant - can be hung up.

Contact dust. This is placed in the burrow, adheres to the rodents fur and is ingested when the animal grooms. Not suited to damp conditions.

Liquid rodenticides. Care must be taken to avoid contamination of food or packaging. Useful if water is scarce.

Contact wicks. Used to control mice. They brush against a brodifacoum-impregnated wick within a protective tube. Poison ingested whilst grooming.

Click on icon for a list of commonly used rodenticides.

Carrying out treatments.
Edible baits should be placed along runs and in areas used by rodents. The use of bait boxes that are tamper resistant and do not allow long necked birds to reach bait are preferable. If using boxes, site 1-5m apart for rats and 1-2m apart for mice. Generally the more baiting points for mice the merrier. The use of bait boxes can reduce bait uptake and prolong treatments. If you have to burrow bait to control rats, use a long handle bait spoon to place the bait within the tunnel and cover with grass to prevent birds pecking. If you are placing around buildings and you are using natural cover to protect bait, please take adequate precautions to prevent other animals getting the bait. When laying bait please keep adequate records to record the following:

• Site map showing locations of bait points
• Initial quantity laid
• Product used
• Date of bait inspections and results at time of inspection
• Dates when dead mice/rats found
  

At end of treatment remove all uneaten bait and burn or bury.
Remove and burn or bury dead rodents.

Click on icon to download rodent control record sheet

Problems you may encounter.

• Bait ignored
• Bait eaten at first then uptakes cease and rodent activity carries on at same level as before
• Bait continually eaten with no reduction in rodent activity
  

Warning dye added to bait helps determine whether you are under baiting.
Choosing the right formulation is important - loose grain is the best formulation. Place down burrows to stimulate feeding from bait boxes.
In dry conditions, liquid baits may be effective so if having problems with dry bait give liquid baits a try.

Resistance.
You may well suspect resistance if you get poor control after prolonged treatment. This may be due to underbaiting, poor bait uptake or re-invasion. Check that these operations are being carried out in a correct manner. If you are satisfied with your operations then it may be worth having the rodent checked by a lab for resistance.
Warfarin resistance is passed on to further generations and can also be found in second-generation chemicals. This is probably cross-resistance from Warfarin. Resistance to first generation anticoagulants by house mice is so great none is used for their control. There is even resistance to second generation anticoagulants (Difenacoum and Bromadiolone).
If you have a situation where you have developed rats with a low-degree resistance to Difenacoum/Bromadiolone then maximise bait uptake. This can be done by using the most palatable bait and where possible, baiting burrows.
In situations where you are trying to control rodents with a high degree of resistance to Difenacoum and Bromadiolone then you must pre-bait. This needs to be carried out for approximately 3 weeks and then switch to a toxic treatment (non-anticoagulant). You will probably only get uptake for about three days maximum. Alternatively, you will have to resort to trapping or if inside, using Brodifacoum/Flocoumafen.

Poison resistance in Norway Rats.

• If resistance to first generation products suspected then use second-generation products
• If resistance to Difenacoum suspected use Bromadiolone
• If resistance to Bromadiolone suspected use Difenacoum
• If resistance suspected to both of the above chemicals use Brodifacoum or Flocoumafen indoors only
• For any form of resistance use zinc phosphide or calciferol and trapping
• If resistance suspected and gassing can be safely carried out use hydrogen cyanide
  

Non-anticoagulants rodenticides.
Calciferol -prebaiting is essential.
Alphachloralose - for mice only.
Fumigant - Aluminium phosphide
Alphacellulose - still awaiting approval under COPR.

For long-term success in rodent control you will need to continually monitor the situation, offer permanent baiting, carry out site maintenance (preventing access), proofing of the site and managing the food supply. Managing the food supply will limit population recovery.

Records.

• It is of the utmost importance to keep and maintain accurate records. Keep these in a central place for ease of access.
• You will need to undergo training and adopt safe working practices. Record staff training details
• Records of use etc. must fulfil legislation and assurance schemes. There are legal obligations you must understand. You must undertake COSHH and risk assessments and keep Safety Data Sheets for the assessments
• All purchases and usage must be recorded. Therefore you must record all amounts purchased and when purchased
• Record name of operator, amount and date of use
• Record numbers of points baited and have a map of the location of bait points
• Record amount bait consumed, date of revisiting bait points and number of carcasses found and how you disposed of them
• Note down areas that need specific attention e.g. proofing and record date when this has been carried out
• After your campaign has been completed, record amount of bait requiring disposal, how you disposed of it and where
  

Acknowledgements. HGCA, CSL.Health & Safety Executive, British Pest Control Association