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Mouse Pest Control

If you are reading this then you are probably researching mouse pest control. Although this article provides a sound over view of mouse pest control, it focuses primarily on how to trap mice in buildings.

How to trap mice in buildings

Mice are very quick at learning to avoid potentially any situation that is dangerous to them so early failures with your trap may lead to your mice becoming "trap-shy" and future trapping can become difficult. We hope that by reading this article you will gain the extra knowledge that will enable you to commence a successful trapping programme.

What species of mouse do you have?

You may think one mouse is the same as another but in the UK there are several species of mice. If it has come indoors it's probably one of two species - a house mouse or a long tailed field mouse. Pest control techniques remain the same for both species.

The House Mouse  The Long Tailed Wood Mouse

The House Mouse (scientific name Mus domesticus) is the most likely mouse to be found indoors. It will survive outdoors in warmer climates but in the UK it prefers the warmth of buildings and finds it rarely necessary to go outside. It has grey-brown fur which is slightly lighter in colour underneath. If you can get close enough you will see that its tail, although long, is about 80% of its body length and its eyes and ears are in proportion to its head.

The Long Tailed Field Mouse, also known as the Wood Mouse (scientific name Apodemus sylvaticus) can also come into buildings particularly if the location is more rural. In contrast to the house mouse it is a chestnut brown colour and white underneath. Its eyes are noticeably bulging and ears large and its tail is about the same length as its body.

For the keen amateur zoologist a more foolproof way of deciding which species you have is that the House Mouse has a notch in its upper incisors which is absent in the Wood Mouse. Pest Control Officers often refer to a Field Mouse as a House Mouse.

Both species of mice are part of a larger group of mammals known as rodents of which there are over 2,700 different species throughout the world. In the UK there are 14 species which include voles, dormice, squirrels, and of course rats. The word rodent is derived from the Latin verb rodere which translates into English as to gnaw. Rodents do not just gnaw for the sake of doing it. They have to continually wear down their paired incisor teeth. Their incisor teeth have only one side covered with enamel and they continue to grow. This growth in rats can be 5 inches per annum, therefore the gnawing keeps these teeth at a reasonable length but because of the one-sided enamel covering also keeps them sharp.

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Why do we need pest control for mice?

Pet mice can be cute and good fun but pest mice can bring unwanted problems to normal life and must be taken much more seriously. They can affect us in several ways.

House mice carry bacteria and viruses the most significant being Salmonella and Lymphocytic choriomeningitis virus (LCMV). Salmonella is an important food poisoning bacteria and so mice in kitchens (and they will certainly be seeking out food) is definitely taboo. Pest mice habits of feeding sporadically in many different areas makes food contamination a certainty and food surfaces, utensils and cutlery and crockery is also likely.

Although mice cannot carry and transmit Weil's disease, they do carry another form of leptospirosis, which, although not fatal, can cause mild illness.

LCMV is a rodent-borne viral infectious disease that presents as aseptic meningitis (inflammation of the membrane, or meninges, that surrounds the brain and spinal cord), encephalitis (inflammation of the brain), or meningoencephalitis (inflammation of both the brain and meninges). Individuals become infected with LCMV after exposure to fresh urine, droppings, saliva, or nesting materials. Pet rodents can also carry LCMV but this is less common.

Mice can produce some 50-60 droppings per night and urinate frequently all over the place. Their strong teeth can damage a wide range of materials and even cause fires when electrical supplies are damaged, when this is the case there clearly is a need for pest control. Mice can also cause phobias in some people and such persons may suffer stress and related illnesses.

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Senses

Mice are largely nocturnal and so their sight is not very well developed. They can detect movement and distinguish light from dark but are almost certainly colour blind. However their senses of smell and touch are very pronounced and are used to good effect. Mice can communicate via chemicals or pheromones excreted by special glands or in their urine. Their hearing is also very acute and they can detect and further communicate in ultrasonic as well as audible frequencies.

Activity and Behaviour

Mice live in social groups which are typically composed of one dominant male, 2-5 females and possibly up to 3 sub-dominant males. The dominant male is exactly that and stays in command by the use of aggressive behaviour to the others in his "harem" especially the sub-dominant males. For them to become a dominant male they will have to overcome, by fighting, a dominant male in their own group or in another. The dominant male ensures there is sufficient food and water for his group but also gets first pickings of everything. Other animals in his group will know if he has been there first by the smell he will leave behind. This marking extends to everything, including traps so others in the group will be reluctant to visit traps if he has first been there.

Generally pest mice will be fairly inactive during the day, preferring to stay in their nests or burrows until dark. Activity is greatest just after sunset and just before dawn. When moving they tend to continually rub their fur against surfaces so they learn their routes to and from their nest. They will leave black marks on such surfaces called smears and these can help in tracing their presence (see later section on detecting mice). How far mice will travel will depend on the proximity of food and water but it will rarely be more than 10m radius of the nest and probably nearer.

Mice are extremely good climbers (they can run up a vertical brick wall!) and will often use the three-dimensional nature of their habitat to exploit a situation. We need to think three-dimensionally when we come to control programmes. They can also gain entry through very small gaps. The rule is if you can fit a pencil through a hole then a mouse can get through!

Generally, unlike rats that are wary of anything new, mice are inquisitive and investigate anything new in their area. We will use this fact later on when we set about trapping the animals.

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Feeding

Mice are very unpredictable in their eating habits and are often described as sporadic feeders. This means they take small amounts of food from many different places. When we lay traps for mice we exploit this behaviour by laying lots of small bait points rather than one big one. They can visit up to 30 different sites in an evening and will take very little food from each site. Although similar in their behaviour, wood mice show a greater tendency to hoard food and will often cache food supplies in many different places.

Their preferred food is cereal based and particularly like grass seeds and canary seeds. In some of our large cities, mice have broken tradition and have shown strong preferences to high protein "fast” foods to such an extent that they cannot digest cereals any more. A mouse will eat approximately 20% of its bodyweight per day which equates to 4g.

Mice will readily drink water if it is available but, remarkably, they can survive their whole lives without a drink. In such circumstances they manage to get the moisture they need from their food. Mice denied free water, however, do not breed as successfully.

Breeding

Your mice are prolific breeders and if left unchecked could soon develop into a heavy infestation requiring considerably more effort with regards to mouse pest control. The female mouse becomes sexually mature at only six weeks with the gestation lasting about three weeks. Unusually in mammals, the female comes into season immediately after giving birth and so can be pregnant with the next litter whilst suckling the previous one. Therefore in ideal conditions a female can give birth to a litter about every 25 days!

In buildings, where temperature and food supplies remain constant throughout the year, mice can produce 5-10 litters of 6-8 young each. A simple mathematic calculation will tell you how quickly a small infestation can get out of hand - a very strong reason for dealing with any initial suspicion promptly.

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Detecting Mice

Confirming the presence or absence of mice is vital in achieving good success with the traps. It's not just finding out if they are there or not - it's also finding out where they are and how many there are. Being nocturnal and shy you may not actually see them but there will be tale tell signs that they are present.

It was mentioned before that they produce 50-60 droppings per night. These tend to be scattered randomly, often on higher objects. Check at different levels inside and on top of cupboards. If you cannot decide if they are fresh or old droppings sweep them up and look again the next day.

House mouse droppings Mouse infested kitchen

Remember never handle mouse droppings as they could contain disease organisms. Always wear disposable gloves and wash your hands thoroughly,
Clean surfaces with Professional Rodent Germ Clear Spray

Earlier it was mentioned that mice leave smear marks behind where they press their bodies against surfaces. You may find these black marks present especially where mice go through holes or around corners.

Smear around toilet Smear around hole

There is a very distinctive smell where pest mice are active. Mouse urine has a strong ammonium like smell which will become stronger the closer to the activity you are.

The use of fluorescent tracking dust can be extremely useful in detecting mouse activity. Apply small patches in suspect areas and then inspect the next day using a UV torch in the dark. The effect is remarkable if not somewhat alarming when you discover how active mice can be during the night. The smallest speck of dust can be easily seen and confirms current activity immediately.

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Trapping your mouse

You have decided that you would prefer to trap your pest mouse rather than poison it. Mouse pest control using poisoning can be an effective way of dealing with mouse infestations but it does have its drawbacks particularly in domestic properties where the presence of children and pets can conflict with poisons. You also have no control over where the poisoned mouse will eventually die and this can lead to unpleasant odour whilst an irretrievable rodent slowly decomposes. Trapping allows you to remove the animal well away from your property so you know it has gone.

Using the knowledge you gained during your mouse detection exercise, you need to place your humane mouse trap(s) in the areas where the mice were found to be the most active. Remember they don't move very far from their nests. The more traps you can lay they more chance you will have of catching the animals. Again remember if the dominant male visits your one and only trap the other mice in his group will avoid it. Also moving the traps slightly on a regular basis can create what appears to be a new object which will exploit the inquisitive nature of the mouse to investigate it.

Mouse Trap Unset Mouse Trap set

Enticing your mouse into the trap can be complex. It can be attracted by food it likes but may be put off by food it does not like. If there is a particular food that you notice is being eaten regularly, use that as the bait. Failing that chocolate is always a good attractant. Mice can be put off by strange smells so try not to handle the traps - use gloves, particularly if you smoke.

Check your traps regularly (at least once per day and preferably twice). If you are away for a weekend or a holiday, do not set the trap but leave it in position tied open so the animals get used to going in and out. This may increase your trapping success when you return.

Once you have caught a mouse you will need to take it up to a minimum of 2 miles away to ensure it will not return. Try to find a place where there is likely to be food and shelter e.g. a thick hedgerow would be good. Release it carefully so has not to harm it and to give it a fighting chance of survival.

What to do after?

Once you have managed to resolve your mouse pest control problem there are a number of measures you can take to reduce the chances of further problems. The mice managed to gain access somehow so try to examine your property for entry points. Typical ones are through airbricks, gaps under doors or in doorframes, through gaps in the eaves (they will climb up vegetation) and other defects. These areas can be proofed to stop further entry. Airbricks can be fitted with framed mesh and the bottom of ill fitting doors can be proofed with bristle strips.

Denying access to food can also help in reducing future infestations. Keeping food in containers helps and clearing away food each evening can also contribute.

In order to be successful mice need a place to live and breed which is safe from predators and has an ample food supply. If you can deny them access to any of these vital requirements you will go a long way to not having a problem again.

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