Rodent Control

Did you know?
The word rodent can be roughly translated as ‘to gnaw’.
Brown rats will consume approximately 10% of their body weight per day.
Mice will eat 2-3g per day.

Selecting the right tool for the job is essential in getting the best results. Not surprisingly the same applies to product selection in rodent control, and an understanding of the differences between the various active substances will help you make the right product choice for effective rodent control.

The two main rodenticide active substances are difenacoum and bromadiolone. Both are second generation anti-coagulants and, to ensure the ingestion of a lethal dose, both require the target rodents to eat more than a single meal. They are therefore referred to as multi-feed baits. Understanding how much rats and mice eat each day, and what lethal doses are needed for effective control will help to give a better understanding of which products are best used in different situations.

A rat will typically eat 25-30g of food in a day, which is taken in about ten small meals, with a maximum consumption per meal of around 3g. Rats are inclined to ignore food sources which are situated in ‘exposed’ locations and if the food is ‘free’ will retrieve it to a place of security and ‘stash’ it there. Mice on the other hand are exploratory feeders and will consume around 3g of food in a day but in many small meals – with a maximum meal size typically around 0.2g. As such, for a bait to be considered as a single feed, the lethal dose must be below 3g of bait for rats and 0.2g of bait for mice.

Table 1: Quantity of finished bait required to generate an LD50 (average lethal dose) in rats and mice

Active Trade names Bait Concentration (PPM) LD50*(g of bait) Brown Rat LD50*(g of bait) House Mouse Application
Difenacoum Roban, Neosorexa, Brigand D, Difenag 50 9.0 0.4 indoor and outdoor
Bromadiolone Rodex, Slaymor, Tomcat, Brigand B, Bromag 50 5.6 0.9 indoor and outdoor
Brodifacoum Vertox, Jaguar 50 1.4 0.2 indoor only
Flocoumafen Storm 50 1.3 0.4 indoor only
Difethiolone Rodilon 25 5.6 1.3 indoor only

Data taken from industry standard figures. LD50 values are shown in grams (to 1 decimal place) for 250g rats/25g mice.  The concentration of active in the baits is the standard commercial rate for that active.

From this we can see that rats could consume a lethal dose of difenacoum, bromadiolone, and difethiolone in around two to four meals, confirming their status as multi-feed baits. Depending on the quality and palatability of the bait formulation then all of these baits can provide a good opportunity for the target pest to consume a lethal dose within one day of feeding, and commonly rats may ingest several lethal doses over the first two to three days of feeding before ill effects are felt. Brodifacoum and flocoumafen are true single feed rodenticides against rats. The data also indicates that difenacoum is by far the most effective of the multi-feed baits against house mice and, when its non-target toxicity profile is considered, should be the product of choice for mouse control. The only true single-feed product for mouse control is brodifacoum.

Difenacoum, because of its remarkable specificity to commensal rodents, has one of the best toxicity profiles of the anticoagulant rodenticides and has been shown to have reduced toxicity to birds and as such has merit for rat control programmes in sensitive outdoor situations such as those where non-target species e.g. birds of prey are in residence. The table below, where figures are available, gives an indication of the toxicity profile of the above rodenticides to non-target animals. These figures should be taken as an indication only; rodenticides should always be protected from non-target animals and in any case of accidental or secondary poisoning you should always consult a vet or doctor.

Table 2 – Non-target toxicity – LD50 grams of bait per kilo of animal

Difenacoum Bromadiolone Brodifacoum Flocoumafen Difethialone
Rabbit 40 20 5.8 14 15
Pig 1600-2000 60 10-40 1200 40-60
Dog 1000 200 5-20 1.5-5 100
Cat 2000 500 500 200 320
Chicken 1000 90 2000

Data taken from WHO and The Pesticide Manual (BCPC)

The figures show that there is a very real difference in the toxicity profile of the different active substances to non-target vertebrates. By comparing target species toxicity with non-target species toxicity a measure of risk can be determined. For instance, flocoumafen and brodifacoum are around six times more effective against rats when compared to difenacoum, though when considering they pose a threat at least 50 times higher to dogs (as an indicative non-target species), the products become considerably less appealing.

Understanding and choosing the right active substance for the job in hand is vitally important due to the significant variation in activity they have against rats and mice and the toxicity to non-target animals. Formulation choice is also important in any rodent control campaign as the rodents must first find the bait and consume a lethal dose. No rodenticide or formulation is completely universal and selecting the right product for a job will minimise environmental risk and save time and money. 19.08.2014

We can’t imagine anyone actually ‘wanting’ to live with rats, unless of course it’s a pet.  As this is usually the case, we have come up with some tips to help you get rid of any you may have discovered in or near your home.

The reason why we want to get rid of rats is first and foremost they carry disease. Probably the most well known is Weil’s Disease which is picked up from their urine.   Less well known is that they also carry salmonella, e.coli, cryptosporidiosis and tuberculosis which humans, as well as pets, can contract.  And finally, there is the more common problem of fleas and mites of various types, and even ticks which all can contribute to allergies.

In all honestly, you are never really far away from a rat.  You may not always seen signs of them but they are definitely around.  If you have a home with a garden, at some point they will attempt to get into the house.  This can be via leaving doors or windows open, or if you have a cat, perhaps the cat flap might be a chance to gain entry.   In fact they don’t even need this much room as they can squeeze themselves through much smaller gaps if determined.  Make sure you check your eves around the house and if there are gaps, this can provide another way in for rats, mice or squirrels.   It’s easy access to your loft from outside if there is room to squeeze in through!

Rats are nocturnal animals and hide away during the day, so they are not usually observed during the day.  However, you will probably see that they have been active and need to be vigilant. Look for droppings scattered about which are like pellets approx 1cm and dark brown.

Some other signs to look for are an unpleasant smell in your home – once you recognise the smell you certainly won’t miss it again!  It is pungent and smells of ammonia.  Sometimes this smell can be detected in lofts, under floorboards, behind a bath panel etc.   Check cupboards for any space around pipes coming in from outside, particularly under sinks and wash basins.  A rat or other rodents could easily come into your home through these gaps, so block any spaces where possible.

Even if you haven’t noticed anything untoward in your home, you should check for possible activity in your garden and garage.   Looks for signs if you have a shed, check under wooden decking or in your garage cupboards.  If you use your garage for storage, check any boxes you may keep in there.  In your actual garden you should investigate any suspicious holes that may have appeared.  Another area that should be checked is your sewer.   If you find any broken areas in the sewer, these should be repaired as soon as possible if you find you have a continuous problem with rats.   There is even a thing called a ‘rat stop’ which can be installed in the sewer.   It will allow water to freely flow but it will stop a rat.

If you have heard any scratching noises above your ceiling, there could well be rodent activity going on in the dead of night.  Therefore you should investigate these areas but make sure you are wearing disposable gloves, and even a mask would be well advised.

Check to see if anything has been gnawed or scratched at, particularly on wood.  They also like plastic to gnaw as they have to grind down their teeth on a continuous basis as they never stop growing, hence the reason why they do this.

Rats will want to establish a home somewhere, ideally where its warm, dry and secluded.   They usually like to line any living areas with newspaper, fabrics and things of this nature to keep them warm.  Rats are prolific breeders and can start producing from 5 weeks of age  and can have litters as large as 14 but 7 is more common.

What do rats like – what will entice them in? Basically two things – most important is food followed closely by a place to set up home for themselves and their offspring.  They must also have a supply of water.  Be careful of how you house your outside bins and make sure that they are completely closed/sealed.  This could provide an easy source of food for rats but also foxes, stray cats, dogs etc.   In the home, do not leave any food out, always put away in fridge or food containers.  In your garden, don’t tempt rats or mice with bird feeders.  Using only squirrel proof feeders would be best and also do not put out water for the birds or other animals.

The best ways of getting rid of rats. You can use approved poisons but make sure where you put down poison is child and pet proof.   Use plastic covers called ‘rat stations’ and if it looks like the bait has been taken, make sure you refill the contents.

Many places sell rat poisons such as DIY stores, supermarkets, garden centres, specialist wholesalers, etc as well as You do not want to endanger your children, pets or the wildlife you are trying to attract into the garden.  If you intend doing this yourself, follow all instructions very carefully to make sure the operation is done correctly.

There are all sorts of different types of rat trap, including humane traps if you prefer choose this route.   There are also ways to drive away the rats by using repellers.  These will emit a sound that humans cannot hear but a rat does not like it.

For a very serious and large-scale problem, or you feel you just cannot cope on your own, then you will have to call in the professionals and there will be many good pest control companies to choose from in your area.

What should I do when the rats are dead? If you have had rats in your loft, or have seen signs of them anywhere in your home but think you have got rid of the problem, make sure you protect yourself with suitable gloves and a mask when cleaning up afterwards. Depending on the scale of the operation wearing disposal overalls and goggles might also be advisable.   Remove any rat bodies, decomposing or skeletons, and spray disinfectant or a solution of bleach mixed with water over the area affected, or where you know they have been.   As they are incontinent creatures they will have urinated all over the place, so please make sure you cover up and protect yourself thereby reducing the  chance of infecting yourself.

Andrew, January 2014