Know Your Enemy January 8, 2012

To a mouse – Robert Burns

“Wee, sleekit, cowrin, tim’rous beastie,
O, what a panic’s in thy breastie!
Thou need na start awa sae hasty
Wi bickering brattle!
I wad be laith to rin an’ chase thee,
Wi’ murdering pattle.”

Winter time is likely to be the time when you start to suspect you have rats or mice (also known as rodents or vermin).   It is cold and food supplies are less plentiful outside – this is often the time when rodents move into the house or buildings around the smallholding. As a nature lover I am happy to live and let live – so what is the big issue about mice and rats?

What is the risk from rats and mice?
Rats and mice spread germs that can cause severe illnesses and disease in humans, some of which can be fatal to humans, although this is very rare.  They can carry  Salmonella and Weils Disease through their droppings and urine.   Campylobacter (Campylobacter infections, can cause diarrhoea and fever. This bacteria is spread via rodents to poultry and thus enter the human food chain  and Leptospira.  The pathogens of this potentially fatal febrile disease are transmitted via rodent urine and can enter the human blood stream through small cuts, for instance.  Mice may also carry tapeworms, and organisms that can cause ringworm (a fungal skin disease) in humans.

Rats and mice can also cause fires by gnawing on cables. Research conducted by the World Health Organization (WHO) has revealed that half of all agricultural fires in Great Britain can be traced back to rodents.

Signs of rodent infestation:

• Sounds. Gnawing, climbing noises in walls, squeaks.
• Droppings. Found along walls, behind objects and near food supplies.
• Burrows. Rat burrows are indicated by fresh diggings along foundations, through floorboards into wall spaces.
• Runs. Look for dust-free areas along walls and behind storage material. A tracking patch made of flour, rolled smooth with a cylindrical object, can be placed in pathways overnight to determine if rodents are present.
• Gnawing may be visible on doors, ledges, in corners, in wall material, on stored materials, or on other surfaces wherever mice are present. Fresh accumulations of wood shavings, insulation, and other gnawed material indicate active infestations. Fresh gnawing marks will be pale in colour.
• Rodent odours. Persistent musky odours are a positive sign of infestation.
• Visual sighting. Daylight sighting of mice is common. Rats are seen in daylight only if populations are high. Quietly enter your barn at night, wait in silence for five minutes and listen for the sound of rodent activity. Look around with a powerful torch; rat eyes will reflect the light.
• Smudge (rub) marks. These may be found on pipes or rafters where dirt and oil from their fur leave a greasy film.

• Urine, both wet and dry, will fluoresce under ultraviolet light, although so will some other materials. Urine stains may occur along travel-ways or in feeding areas.

“It is a generally accepted rule of thumb that there are approximately 25 mice or rats for every one that is seen.”

Why Control Rodents?

Damage from rodents comes in many forms:

• Damage to buildings. Mice and rats will damage wood and electrical wiring, which can be a fire hazard.
• Destruction of insulation. Many livestock and poultry facilities show serious deterioration within five years. Associated with this damage are costs for re-insulation, increased energy costs and poorer feed conversions by animals.
• Feed consumed. A colony of 100 rats will consume over 1 tonne of feed in 1 year.
• Feed contaminated. A rat can contaminate 10 times the amount of feed it eats with its droppings, urine and hair. A rat produces 25,000 droppings per year, a mouse 17,000.
• Biosecurity. Rodents are recognized as carriers of approximately 45 diseases, including salmonellosis, pasteurellosis, leptospirosis, swine dysentery, trichinosis, and toxoplasmosis. Mice and rats can carry disease-causing organisms on their feet, increasing the spread of disease.

Is It A Rat Or Mouse Problem?

Since rats and mice require different control strategies, you should determine which vermin you have. The simplest way to differentiate between the types of infestation is by examining the droppings.

Droppings

Mouse droppings are black and rice-kernel size, whereas rat droppings are black and bean-sized.

Breeding

Mice and rats have tremendous breeding potential. Under ideal situations, a pair of rats and their offspring can produce 20,000,000 young in 3 years. Mice reproduce even faster.

Life expectancy of a rat is around one year, during which female rats will typically breed five times and produce an average of 8 offspring. A mouse life expectancy is around one year, during which a female may breed up to six times and produce about six offspring.

Mice prefer to nest in dark secluded areas with little chance of disturbance. They may burrow into the ground in fields or around structures when other shelter is not readily available. Nests are constructed of shredded fibrous materials such as paper, and generally have the appearance of a “ball” of material loosely woven together. They are usually 4 to 6 inches (10.2 to 15.2 cm) in diameter.  Foraging territories are no more than 6 metres away. If there is abundant food nearby they can nest within 1.2-1.6 metres of the source

Litters of 5 or 6 young mice are born 19 to 21 days after mating, although females that conceive while still nursing may have a slightly longer gestation period. Mice are born hairless and with their eyes closed. They grow rapidly, and after 2 weeks they are covered with hair and their eyes and ears are open. They begin to make short excursions from the nest and eat solid food at 3 weeks. Weaning soon follows, and mice are sexually mature at 6 to 10 weeks of age.

Mice may breed year-round, but when living outdoors, they breed mostly in spring and autumn. A female may have 5 to 10 litters per year. Mouse populations can therefore grow rapidly under good conditions, although breeding and survival of young decline markedly when population densities become high.

Senses

Rats and mice have poor eyesight but excellent senses of smell, taste, touch and hearing. They do not like open areas and prefer contact with walls and other objects.

Mice are considered color-blind; therefore, for safety reasons, baits can be dyed distinctive colors without causing avoidance by mice, as long as the dye does not have an objectionable taste or odor.

Habits

Rats and mice move rapidly and are excellent climbers and have no problem climbing vertical brick walls. They are also active burrowers and like to build nests in compost heaps or underneath hedges, sheds and decking. In the house they will nest in wall cavities and beneath floorboards. They are mainly active at night feeding on a range of commodities, particularly cereals and cereal products. They will eat about 10% of their own body weight of food daily. Rats require a regular supply of water, whereas mice do not as there is normally enough to survive on in their food. Rats are also good swimmers and are often found in sewers where there is food, water and shelter.

The front teeth of rats grow continuously and to keep the teeth to a useful length the rat needs to gnaw on hard objects all the time; objects can include lead water pipes, brickwork, electric cables, wood and anything else available. They usually have well worn runs between their living area and their food and water sources.

Mice will easily enter gaps of 5mm wide and they are very good climbers.

If a pencil fits in a gap, then a mouse can get in!

House mice eat many types of food but prefer seeds and grain. They are not hesitant to eat new foods and are considered “nibblers,” sampling many kinds of items that may exist in their environment. Foods high in fat, protein, or sugar may be preferred even when grain and seed are present. Such items include bacon, chocolate sweets, and butter (a little melted chocolate is a favourite in our mouse traps).

They do not range far from the nest. The maximum range for rats is 45 m (148 ft), for mice 9 m (30 ft). Rats are extremely apprehensive about new objects and will avoid them for several days. Leaving a trap out for about 5 days is necessary to ensure acceptance. Mice quickly accept new objects. This becomes very important when designing baiting or trapping programs.

Damage

Rats and mice will invade buildings in search of food and shelter. In doing so they may be involved in the transmission of disease, soiling and destroying belongings, damaging equipment and can cause serious structural damage by gnawing through cables, waterpipes and woodwork etc. They also eat and destroy food stores.

Did you know?

• mice are sexually mature at 6 to 10 weeks of age?
• worldwide, rats transmit roughly 40 diseases?
• unlike mice, rats avoid anything new? They only take tiny amounts of freshly laid-out bait and often avoid new traps completely.
• rats do not just eat food leftovers, but also soap and paper, dead mice, birds and fowl
• a rat produces 25000 droppings per year, a mouse 17000.
• rats and mice are highly adaptable creatures. Some of them have even developed resistance to rodenticides

Controlling and reducing vermin such as mice

The next step in controlling a rodent problem is to reduce the population with a combination of baits, traps, and cats.  It is best to ensure that you set up a programme of activity that is overseen by you – some of the work can be undertaken by other people such as private pest control companies, or your local authority pest control officer.  However, this will be an ongoing matter that will require you to be vigilant and pro-active.

Prevention – Reducing rodent infestations

Eliminating Hiding Places and Nesting Sites

Rodents do not like to be exposed. Maintain sound housekeeping, eliminate loosely piled building materials, old feed bags or anything else that a rodent can hide in or under.

“Best practice says that when cleaning you should let it air for 30 to 60 minutes, and if you find mice droppings or you find nesting material, you should spray it with a 10% bleach solution or disinfectant, and let it soak in for a while.  Ideally you should never sweep or vacum the droppings because this puts infectious matter into the air, where it can be inhaled.  The best bet is to clean with something disposable whilst wearing rubber gloves.”

Remove Food and Water

Eliminate water sources such as leaky taps, open water troughs, sweating pipes and open drains. Keep all feeds in rodent-proof bins, covered cans or metal hoppers. Reduce feed spillage and immediately dispose of dead animals. Without readily available food and water, populations cannot build.

Mice and Rat Predators

Some dogs  and cats will catch and kill mice and rats.  Cats may limit low-level mouse or rat populations.  However, if conditions are ideal for rodents, cats cannot eliminate a problem because they are not able to catch mice as quickly as they multiply. Cats may also introduce disease into a facility by bringing in rodents caught in fields.

Around most structures, mice can find many places to hide and rear their young out of the reach of such predators. Cats probably cannot eliminate existing mouse populations, but in some situations they may be able to prevent reinfestations once mice have been controlled. Farm cats, if sufficient in number, may serve this function.

Noise

Mice are somewhat wary animals and can be frightened by unfamiliar sounds or sounds coming from new locations. Most rodents, however, can quickly become accustomed to new sounds heard repeatedly.  There is little evidence to suggest that rodents’ responses to no-specific, high-frequency sound (ultrasonic sound) is any different from their response to sound within the range of human hearing.  Tests of commercial ultrasonic devices have indicated that rodents may be repelled from the immediate area of the ultrasound for a few days, but then will return and resume normal activities.

Repellents

Rodents find some types of tastes and odors objectionable, but chemical repellents are seldom a practical solution to mouse infestations. Substances such as moth balls (naphthalene) or household ammonia, in sufficient concentration, may have at least temporary effects in keeping mice out of certain enclosed areas.

Other solutions to rodent problems, including rodent-proof construction and methods of population reduction, are usually more permanent and cost-effective than the use of repellents.

Toxicants

Anticoagulants (slow-acting, chronic toxicants). Mice are susceptible to all of the various anticoagulant rodenticides , but they are generally less sensitive (often far less sensitive) to the active ingredients than rats.  Anticoagulants have the same effect on nearly all warm-blooded animals, but the sensitivity to these toxicants varies among species. Additionally, residues of anticoagulants which are present in the bodies of dead or dying rodents can cause toxic effects to scavengers and predators.

Anticoagulant Resistance

Within any population of  mice, some individuals are less sensitive to anticoagulants than others. Where anticoagulants have been used over long periods of time at a particular location, there is an increased potential for the existence of a population that is somewhat resistant to the lethal effects of the baits.

Anticoagulant Bait Failure

Resistance is only one (and perhaps the least likely) reason for failure in the control of mice with anticoagulant baits. Control with baits that are highly accepted may fail for one or more of the following reasons:

• Too short a period of bait exposure. —Insufficient bait and insufficient replenishment of bait (none remains from one baiting to the next).
• Too few bait stations and/or too far apart. For mice, stations should be within 6 feet (2 m) of one another in areas where mice are active. —Too small a control area, permitting mice to move in from untreated adjacent areas. —Genetic resistance to the anticoagulant. Although this is unlikely, it should be suspected if about the same amount of bait is taken daily for several weeks.

Reasons for failure to achieve control with anticoagulant baits :

• Poor bait choice, or bait formulated improperly. Other foods are more attractive to the mice.
• Improperly placed bait stations. Other foods are more convenient to the mice.
• Abundance of other food choices.
• Tainted bait: the bait has become mouldy, rancid, insect-infested, or contaminated with other material that reduces acceptance. Discard old bait periodically, and replace it with fresh.
• Occasionally, mice accept bait well and an initial population reduction is successful. Then bait acceptance appears to stop although some mice remain. In such instances, it is likely that the remaining mice never accepted the bait, either because of its formulation or placement. The best strategy is to switch to a different bait formulation, place baits at different locations, and/ or use other control methods such as traps.

“Never place bait stations where livestock, pets, or other animals can knock them over. Spilled bait may be a potential hazard, particularly to smaller animals.”  If misused, anticoagulant rodenticides can be lethal to non-target animals such as dogs, pigs, and cats.

Rodent droppings and pigs

The causative organism of Erysipelas in pigs is the ubiquitous bacterium Erysipelothrix rhusiopathiae, formally known as Erysipelas insidiosa. The bacterium can survive in soil or dung for 6 months or more but probably more significantly is carried by a wide range of wild birds as well as rodents, especially mice. Pigs are particularly susceptible to disease with this organism and the classical manifestations are the acute, septicaemic form producing sudden deaths or in milder cases “diamonds”. These forms of the disease can be controlled by a combination of hygiene, medication and vaccination.

Mice have also been found to act as reservoirs or transmitters of diseases of veterinary importance, such as swine dysentery, a serious bacterial disease of swine often called “bloody scours.”

Rodents and poultry
It has been estimated that rodents can increase poultry feed ussage by as much as 2% especially in the cold weather. Rats and mice are likely to find poultry houses a great place to live. Rodents spread diseases to poultry flocks by contaminating feed and bird living area with urine or droppings. Rats and mice are linked to poultry diseases such as salmonellosis, colibacillosis, coryza, pasteurellosis, mycoplasmosis, hemorrhagic enteritis,hymenolepiasis, capilariasis, and ascaridiasis. Because of their ability to harbor pathogens, rodents also can carry over disease organisms from one flock to another even if the facilities are cleaned and disinfected.  Rodents also carry parasites such as lice, fleas, and mites.

All types of rodents eat poultry feed and they waste and contaminate more than they eat. It has been suggested by some authorities that one rat eats approximately 25 pounds of feed per year.   In addition to damage and feed loss rodents can cause high mortality rates and production losses. Rats have been known to kill baby chicks and break and eat eggs, and they may frighten birds by their movements or by noises they create.  Research has shown that by reducing the rodent population in poultry houses the bird mortality rate can also be lowered.

Rodent proofing a building

• Concrete: Concrete should be 2 inches thick if made of precast reinforced concrete plates fastened together, or at least 3¾ inches thick if not reinforced.
• Galvanized Sheet Metal: 24 Gauge or heavier; perforated sheet metal or grills should be 14 gauge.
Brick: Regular size, 3¾ inches thick with joints filled with mortar.
• Hardware Cloth: 19 Gauge ½ by ½ inch mesh to exclude rats, 24 gauge, ¼ by ¼ to exclude both rats and mice.

Any openings that are needed for ventilation should be screened or rodent proofed to prevent rodent access. With elimination of entry points, any potential hiding places outside the house should also be eliminated. Obvious food sources such as spilled feed should also be eliminated, use hanging feeders and remove any uneaten food before nightfall.

In some instances, a strip of heavy gravel placed adjacent to building foundations or other structures will reduce rodent burrowing at these locations. In any event, keep the perimeter of buildings and other structures clean of weeds and debris (including stacked lumber, firewood, and other stored materials) to discourage rodent activity and to allow easier detection of rodent sign.

However, any drastic change to their habitat may cause rodents to abandon their habitat. However they will only move to the next building or into the woods to wait until the coast is clear to return. Therefore the best plan is to elimate the rodents before undertaking a major clear-up.

Livestock Food storage – making it vermin proof

Where possible, store bulk foods in rodent-proof containers or rooms. Stack sacked or boxed foods in orderly rows on pallets or tables in a way that allows for thorough inspection for evidence of mice. In such storage areas, keep stored materials away from walls.  Sweep floors frequently to permit ready detection of fresh droppings.

When storing foods or feed on pallets, keep in mind that mice can jump up more than 12 inches (30.5 cm) from a flat surface. They are also good climbers and can walk up surfaces such as wood or concrete (unless the surfaces have a slick finish). Mice can live for considerable periods of time within a pallet of feed without coming down to the floor.

Useful links

• Rodent factsheet http://www.salford.gov.uk/d/insect12rodents.pdf
• Info http://icwdm.org/handbook/rodents/HouseMice.asp
• Erysipelas Associated Lameness link this fact sheet to the pig page http://www.nadis.org.uk/DiseasesPigs/erysipelas%20associated%20lameness.pdf
• Link to Burns poems http://www.rbwf.org.uk/poems/translations/554.htm
• Link to grow herbs to deter pests http://www.wikihow.com/Grow-a-Pest-Repellent-Herb-Garden