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norway ratThrough the summer months the natural population of rats and mice rises as increasing quantities of food such as fruits, nuts and grains are available to them. Once autumn arrives, food sources dwindle and temperatures drop. Consequently rats and mice then begin to look for shelter and alternative food supplies. All too often they find both in our homes, sheds, chicken houses, stables and stores. Also, all too often we don't do anything about this inevitable invasion, at least not until they have moved in, set up home and begun to raid the food available.

Rats and mice are well known to gnaw on cables causing short circuits and sometimes fire. They will gnaw pipes causing floods. They continually dribble urine and defecate regularly; mice produce up to eighty droppings per day. They will eat our and our animals food which is a risk to health. And they cause consternation to those with a natural fear of rodents.

Now is the time to prepare for and prevent rats and mice moving indoors to live with you or your animals.

Here are a few simple steps to staying free of rats and mice.



Stop rats and mice finding a way into your home or other building. Take half an hour to walk around the house and outhouses looking for ways rats and mice might get in. Take a pencil with you to write down what needs to be done and use it to measure gaps. If a pencil can slip under a door a mouse can get under it. Mice and rats can flatten their rib cages to fit through gaps, if their head can fit through, their body can follow.


Gaps under doors can be sealed with draft excluder. Gaps around pipes and cables can be filled with mortar, filler or polyurethane foam. Although rodents can eat through foam, and even concrete, they won't unless the sealed gap is somewhere they have travelled many times before.

Sheds and outhouses, particularly old ones, may have many possible entry points. It may not be possible to seal them all, but I would recommend sealing as many as you can. It all helps to reduce the risk or rodents finding their way in.

Look in places both high and low. Rats and mice are excellent climbers. Roof rats are better climbers than the larger Norway rats and spend a lot of time feeding in trees. They will walk along branches that overhang roofs and drop down onto the roof. From here they rarely have difficulty getting into the roof void via gaps around the eaves. Cut overhanging trees away from the roof and also trim climbing plants such as rambling roses, vines, ivy, honeysuckle etc. to at least 30cm below the overhanging eaves.

Air vents are necessary for the good ventilation of sub floors and should not be sealed. Undamaged vents are usually designed to be mouse proof. Repair damaged vents or cover with fine mesh. Also look for gaps where pipe work and cables enter buildings and gaps where weatherboards do not fit flush. These can usually be filled with silicone sealers, waterproof fillers or foam filler.

It is also worth taking a look around the interior of the building for gaps that can be sealed. Make the building less attractive to rodents by making it harder for them to travel through. Sealing gaps around pipe work and cables is particularly helpful as the cables and pipes often run through walls making great highways for rodents.

Rats and mice are usually active at night and are not likely to gain entry through open doors and windows during the day. The exception might be when they are under real pressure to find food and shelter. Then they may take the risk of venturing out during the day. So keep doors and windows closed at all times if possible.

Remove Cover

As mentioned previously rodents do not 'like' to be in the open. So don't give then cover around your home or buildings. Don't let the grass grow too long. Don't have piles of timber, corrugated iron, etc. piled against walls. Have a perimeter of open ground which rodents would have to cross to get to your buildings.

Remove Food Sources

Remove all food sources. In your home check for food that might have been spilled behind the fridge or under other furniture. Make sure the cereals, flour, rice and other food stuffs in your larder are put in sealed containers.

In sheds, stables, chicken houses and stores put all food in sealed containers. Use metal containers if possible. Rodents can gnaw through plastic with ease but plastic bins are better that paper bags or no covering at all.

Feeding troughs can sometimes be placed so that the animals being fed can reach the food easily but rodents will find it mote difficult. It is often not possible to prevent rodent access entirely, but it is worth making it as difficult for them as possible. E.g. hang chicken feeders from a cable. Make the rodents jump up or climb down to reach the food.

Baits and Traps

Nowhere can be made 100% proofed against rodents and you may already be too late to stop rodents entering. So place baits and traps in position NOW. This will also mean that the baits and traps are ready for any rodents that gain entry by some route not found during your search. Deal with them before they become a problem.


Almost all toxic rodent baits contain anti-coaglulant (AC) toxin related to the original warfarin. However, there are two main groups of anti-coagulant; first and second generation ACs.

Second generation ACs such as brodifacoum and bromadialone work more quickly but the toxin lasts longer in the dead or dying rodents. This means there is an increased risk of secondary poisoning of animals that might scavenge on them.

First generation ACs such as coumatetralyl can be as effective, but they are safer and eco-toxic because they poses a lower risk of secondary poisoning. So safer for pets and there is a reduced persistence of the toxin in the environment.

If toxic baits are not an option there is a natural organic certified rodent bait that is effective, but does not contain any toxin. It is therefore safe around pets. The bait is lethal to rodents because they are alone in not having the correct enzymes to digest the cellulose that the bait is made from. Note: this bait is only effective in dry conditions and where other food sources can be removed.

Baits come in several forms but most are based on grains. Some bait blocks are waxed to make them weatherproof and last longer outdoors or in damp conditions. There is also a bait a tracking powder available. This product is useful where other food sources cannot be removed meaning it is difficult to get the rodents to eat bait. The bait may be eaten or the rodents may take in the toxin after running through the tracking powder and licking it off their paws or fur.

Place baits in areas where rodents will travel. Place the baits under cover in bait stations, in a length of pipe, under blocks, in roof voids, etc. Rodents prefer to feed while under cover and cover keeps non-target animals such as pets and birds away from the bait.

Roof rats hoard food. So baits should be crumbled or fixed in place so that they cannot take the bait to their stash and must eat it where it is.


Traps are rarely sufficient on their own to get rid of an infestation of rats or mice. However, they will be effective at catching 'dopey' rats and mice that have had a feed of bait, they are good for additional control in areas where toxic bait cannot be used and where you want to be sure the bodies can be removed.

The best lures for traps are peanut butter or chocolate but these have a limited life and need to be replaced regularly. Placed correctly traps are almost as effective without bait. Place traditional snap traps at right angles to, and against walls where rats and mice would travel. Rats and mice are generally reluctant to move into open space and prefer to stay close to some vertical surface or stay in enclosed places.


Electronic, electromagnetic and sonic devices can be useful at encouraging rats and mice to choose next door to live, but should not be seen as a way of getting rid of rodents that have already set up home. Rats and mice are wary of new things in their environment and will be quietened by such devices for a short period. But they become used to new things after about two weeks. It is better to stop them entering in the first place. It would take a lot to make you move out of your home!

Be Pro-Active

Don't wait for a problem to arise. Put checking rodent defenses on your list of regular things to do. Checking and replenishing, traps, baits, entry point seals and housekeeping should be done at least every three months, and more often where rodents are common.

Late summer and early autumn is the time of the year that rodents are most likely to invade. But be ready for them all year round.

Follow these simple steps and you can sleep soundly in the knowledge that you are not sharing your home with rats and mice.

‘The Pest Advice’ – by David Brittain

David has worked in pest control since starting work with Rentokil in the UK in 1982. He worked for the Department of Agriculture of Northern Ireland for 8 years studying DNA typing and the epidemiology of bovine tuberculosis before starting his own pest management business. David moved to New Zealand in 2004 and joined Target Pest to set up an urban pest management division and manage marketing for the company. He moved to Kiwicare in 2007 and has been involved in promoting proper use of pesticides and developing new products. David is a member of the executive of the New Zealand Biosecurity Institute and webmaster for the NZBI, Kiwicare, KCL Commercial, Aldwin Paige and writes the Pest Advice Blog.

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