Course: Rat control | Last Updates: 7th October 2015
Climate change will lead to an increase in rat populations, said 74% of farmers, gamekeepers and pest controllers in a recent Campaign for Responsible Rodenticide Use (CRRU) survey. Based on evidence they see in their work, the following assessed farm rat populations as:
- rising – 61%
- static – 30%
- falling – 9%
The scale of the problem
Almost half of all farm fires are thought to be started by damage from rats. They eat an estimated 210t of animal feed and cereals a day in the UK, and contaminate what they don't eat with faeces and urine. They also carry fleas, mites and multiple disease organisms including cryptosporidium, campylobacter, listeria, toxoplasma, salmonella and leptospira.
The Health Protection Agency has reported 42 confirmed cases of leptospirosis in humans during the past year. Not all cases could be linked to a potential cause, but among those where this was possible, one in four were farmers. One of the 42 cases was fatal.
Farmers are required to control rats (and other vermin) for compliance with farm assurance schemes. But the scale of the problem is enormous.
Estimates of the UK rat population vary from 80m to 10.5m. But the imperative to control rats is matched by the need to do so responsibly. Indiscriminate or ill-disciplined use of rodenticides poses all manner of threats to the farming and rural community. Children, pets and non-target animals are all at risk of poisoning from poorly-positioned baits. Predatory birds – including red kites, barn owls and kestrels – are at risk of secondary contamination if they eat the carcasses of rats killed by rodenticide which have not been collected and disposed of promptly.
Moreover, government surveillance of pesticide use and wildlife casualties means that perpetrators of irresponsible rodenticide use face identification and prosecution.
Rats are adapted to survive and thrive. They live in large hierarchical colonies and range over a familiar area (their "home range"), normally no larger than they need to find sufficient food, water and nesting places. If a large proportion of a rat colony is killed, it is thought that the rest will increase their reproductive rate to restore the old population level. So a control programme should be designed and implemented for complete elimination; half measures are a waste of time and money.
Rats have excellent senses of smell, taste, touch and hearing. Though their sight is weak, this is made up for by the ability to remember a complex sequence of muscle movements, called kinaesthesis. They move around their home range relying on this ability and may, for example, continue to move around the location of objects that have been taken away. They are also cautious about new objects placed in their home range, which explains why new baiting points may appear to be ignored by rats for several days initially.
Usually, rat infestations have an existing and abundant food supply and they will not switch quickly from reliable and trusted food to a new one such as rodenticide bait. So before introducing bait, eliminate other food sources and render the target rat colony hungry so they are more likely to take bait in lethal quantities quickly.
An effective rat control initiative has three parts:
- Baiting and killing to eliminate target rat colonies.
- Rodent-proofing sensitive areas to prevent access.
- Cleaning and tidying to deny food and shelter and make the site as unsuitable as possible for a new colony.
To ensure that you comply with what is recognised as responsible (and effective) practice, follow the seven-point CRRU code:
- A planned approach. Study the location of the infestation carefully and identify the colony's home range. But don't tidy up or move things yet because disturbance may deter rats from taking bait or even displace them to another location. Draw a plan of the target area.
- Use enough baiting points at locations all over the target home range. Mark each location on the site plan. Half measures are pointless. Using enough baiting points from the outset will minimise the time taken for control to be achieved and also reduce exposure time for non-target species.
- Record quantity of bait at each location then note signs of rat activity at each point as the treatment period progresses. Follow the rodenticide label instructions accurately.
- Collect and dispose of rodent bodies regularly both during and after the treatment period. This is one of the most important points on the CRRU code. The carcasses may contain rodenticide and, if eaten by predators or scavengers, could be a source of wildlife exposure. Dead rats may be found for several days after eating bait and they may die 100m or more away from the baited site. Dispose of rodent bodies as recommended on the product label.
- Never allow bait to be exposed to non-target species. Where possible, use materials already in the target home range (eg, concrete blocks, slates, bricks, corrugated sheets, etc) to protect bait from rain, dust and access by non-target species. Tamper-resistant bait stations are available and offer the highest level of protection of the bait from non-target animals and human contact. Use these where covers made of other materials may not be secure enough.
- Inspect every bait location regularly, as recommended on the product label, and replenish accordingly. Keep a record of each inspection, what you found and any action taken. This is important, as you are subsequently required to demonstrate good practice. Also be alert for signs of disturbance by non-target animals.
- Remove all bait from every location at the end of the treatment period and make a record on the site plan that you have done so.
As soon as the treatment period is over, it is essential to make sensitive areas rodent-proof, and generally clean and tidy the entire site to minimise its suitability for recolonisation. If this isn't done, a new colony will be established and you'll be back to square one.
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