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House Mouse - Fact File

Size: 7-9cm (head + body length). Tail 80% body length. 10-25g (average about 15g).
Markings: Grey/Brown fur, slightly lighter undersides.
Location: Just about anywhere that man is found, and more.
Detection: Customer will report live sightings, scuffling noises, droppings and gnawed goods, smell. Nesting materials sometimes seen.

Biology:

Rodents are well-studied, and in-depth facts of their biology, behaviour and treatment should be sought. Important details are summarised below.

The house mouse arrived in Britain around the 10th century BC, but originally it was a wild species, coming from the Steppes of Russia and the surrounding areas. Although it is not originally a native species, it has made itself very much at home, and is now common throughout rural and urban Britain. It associates itself with man in almost all his environments, but it is not found in sewer systems.

The mouse is a rodent, one of over 1500 species of mammals belonging to this group, although only 15 are present in Britain. It can be easily placed in this group by looking for the single pair of upper and lower front teeth called incisors. They have no canine or premolar teeth, but they do possess molars at the rear of the jaws. There is a noticeable gap between the incisors and the molars, known as the diastema.

The incisor teeth of rodents grow continuously throughout the animal's life and so a mouse must gnaw on objects to keep them worn down and at a manageable length. The molar teeth do not grow continually. The incisors are strongly curved and have enamel on one side only, allowing a razor sharp edge to develop. This means that mice can bite through wood, soft metals and even soft stonework with ease - modern food packaging presents no problems.

Reproduction rates of mice are impressive, and in theory nearly 2000 offspring in one year could result from just one pair of adults (1 doe + 1 buck), given ideal conditions. After mating there is a gestation period of 21 days before 5-6 young are born. At birth, baby mice weigh just 1 gramme. They are weaned after only 3 weeks and sexually mature after only 8-12 weeks. Each female can have up to 10 litters in a year. Mice can live up 10 2 years in the lab, but usually live less than 12 months in the wild. They are fiercely territorial.

Like all rodents, mice require a balanced diet, and can be thought of as omnivores. Historically, mice tended to feed on products of cereals and grasses, and so they tend to prefer rodenticides containing grains etc. They can also eat a wide range of other foods including vegetables, fruits, fish, insects and meat. They are also cannibalistic, and will eat each other. Local food preferences should always be taken into account when planning a treatment regime. Mice are inquisitive but erratic feeders, and will eat 3-4g a day. They will drink when a water source is available, but they can get sufficient moisture from their food.

Mice have the same 5 senses as humans, but their touch, smell and hearing are particularly keen. They cannot see colour, but are good at detecting movement.

Treatment:

Inspection of the premises will enable you to determine the level and extent of infestation, by looking for the various signs of their presence. These include a characteristic 'musty' smell, sightings of mice, droppings (do not be fooled into thinking you have a large infestation just because there are a lot of droppings - mice can produce 50-80 droppings per mouse per night in times of plenty), hairs, runs, smears from their greasy fur and urine pillars in habitually used latrines. Time spent assessing this information during the initial survey and subsequent treatment is essential in gaining control of an infestation.

1. Baits When feeding, mice are cautious, but they do not usually tend to exhibit neophobia (new object reaction). They are beginning to show behavioural resistance, where certain foods (baits) are avoided. The reasons for this are not yet clear. When planning a baiting programme, it is important to consider what foods the mice are currently eating. Scrupulous hygiene is vital as other food sources will impede successful treatments.

Modern rodenticides tend to be single-feed-kill anticoagulants which affect the clotting of the blood and cause death by blood loss. Their action is quite slow, taking from 3-10 days. The antidote for anticoagulants is Vitamin K1 (Phytomenadione). Other chemicals such as Calciferol, which affects calcium metabolism, are also used as rodenticides. Bait bases can include block, soft wax, or loose grain, but a canary seed bait base is particularly successful. In areas where behavioural resistance is suspected, some experimentation with bait bases may be necessary - consult your pesticide supplier for advice.

Baits should be placed in trays or boxes along runs or behind fixtures. Tamper-resistant bait boxes may be necessary when there is a risk of non-target species gaining access to the bait points. A COSHH assessment should be carried out to ensure safe use and placement of baits. Bait points should be inspected at least weekly, replenished where necessary, and removed after a successful result has been achieved.

2. Liquid Baits These are not usually used for mice unless there is an abundance of other foodstuffs or the environment is particularly dry. Liquid rodenticides are anticoagulents that are diluted with water, placed in liquid feeders and treated in a manner similar to baits.

3. Dints Dust formulations containing rodenticides are useful in runs that can be identified or in voids / cavities that are thought to harbour mice. The dust adheres to the mouse's fur and is ingested by grooming. This method is useful as it does not require the mice to feed, but care should be taken as the dust can get easily blown or trodden on sensitive areas such as food preparation surfaces.

4. Traps Traps are still an excellent method of mouse control. Bait with apple, bacon rind or chocolate and place at 90° to the wall. Live traps are also good, but must be visited daily. Glueboards should be considered as a very last resort, as their use is strictly monitored.

5. Proofing Exclusion should always be the primary methods of control. All gaps greater than 6mm must be sealed using mortar, mesh or brushstrip.

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