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Bank voleBank vole

BANK VOLE

Habitat

Bank voles are the most common mammal in Europe. They can be found all over Central and Northern Europe. In the South they occur only in the mountains and moist wood land. They live in deciduous and mixed forests, hedgerows, field verges, parks and gardens. They like humid areas like bogs and riverbanks with dense vegetation and bush cover that provides protection from predators and is a source of food. Bank voles love ferns and bramble. They are rarely found in open spaces or on cultivated land. Bank voles also inhabit huts, sheds, barns, and other wooden structures, but they rarely enter residential buildings.
 
Here Bank voles have colonized both, the sheds and the piles of wood.

Stored building materials providing hiding places for bank voles. Copious droppings on the bricks confirm the infestation.

Lifestyle / behaviour

Bank voles are active day and night. They don´t not hibernate.

They build their nests in shallow burrows or above ground in sheltered places. The nests are spherical and are constructed from twigs, leaves, fibres and moss. The burrows are only a few centimetres below the surface and always have several exits. In addition, bank voles build networks of partially covered walkways in ground-covering layers of vegetation and foliage.

 
A bank vole with its nest in a hollow tree trunk.

Bank voles live in colonies. The population density varies throughout the year and surges every 3-4 years. In a ‘normal’ year there are 6-12 voles per hectare and up to 100 per hectare in years of super-prolific reproduction. Depending on the amount of food available, the size of a single female’s territory is from 500sqm to 2,000sqm. The females’ territories overlap. The territory of a single male covers several females’ territories and is up to 15,000sqm. 

When they reach sexual maturity, the young males must leave their father’s territory and occupy a territory of their own. Daughters may stay as long as they are accepted by the other females. This means that it is mostly younger and weaker males that inhabit the outer boundaries of a colony where conditions are the most unfavourable. 

Bank voles are good climbers and climb bushes and trees up to several metres high in search of food.

 
Bank vole climbing a raspberry bush.

Bank voles gather and store food like acorns, nuts, seeds, plant stalks and leaves in places such as cavities in tree trunks and food chambers in their burrows. Forgotten and abandoned food stores play an important role in the propagation of trees and plants that bear edible nuts and fruits.

Bank voles occupy the same natural habitats as wood mice and yellow-necked mice. Where there is strong competition from these larger, stronger mice, bank voles shift their activities to the daytime to avoid these strictly nocturnal rivals.

Bank voles are plentiful throughout the year and are an important food source for many predators such as owls, birds of prey, martens, foxes, cats, weasels, stoats and snakes. In the years of huge increases in numbers, the populations of predators also increase. The bank voles’ defensive strategies are high rates of reproduction, hiding in dense vegetation, traveling through covered runways and moving around very quickly. They also react appropriately to the warning calls of birds.
Bank voles have excellent hearing and their auditory range includes ultrasound. During courtship, males sing ultrasonic songs to the female. The calls of babies are also ultrasonic.
 

Nutrition

Bank voles are in the main herbivorous. Depending on seasonal availability, they feed on seedlings, blades of grass, herbs, roots, moss, mushrooms, bark, beechnuts, acorns, seeds, nuts, berries and fruits. Sometimes they will eat insects, spiders and worms and occasionally birds’ eggs. In spring their diet consists mostly of green plant matter. They are particularly keen on hazelnuts and blackberries. In winter they gnaw the bark off young trees such as beech, maple, larch, Douglas fir and elder.

 
A Bank vole gnawing into a hazelnut.

3g - 6g of food is needed daily.
 

Reproduction

  • Litter size: 2 to 8 pups, mostly 5 to 6 
  • Number of litters per year: 3 to 4
  • Sexual Maturity: females 6 weeks, males 8 weeks
  • Gestation Period: 19 to 22 days
  • Breeding Season: February – October and, if food availability is good, they also breed in winter. 

The combination of early sexual maturity and innumerable litters with many pups per litter results in population proliferation. In winter the mortality is high, so spring populations are small. But numbers build up quickly over the summer months and reach a peak in autumn. Every 3-4 years, triggered by an abundance of foods like beechnuts, acorns and berries, mass propagation occurs producing up to 100 bank voles per hectare.

Both males and females sometimes kill the litters that are not theirs. 

A young migrating male that has not yet established its own territory will sometimes kill a female’s pups before mating with her to ensure that only his offspring will enjoy parental nurturing. An established dominant male protecting a territory will not do this. That is why females tend to favour dominant males and actively avoid or drive away migrant males. 

When the population density is high, regular social structures and territories collapse and there is extreme competitive pressure. Females will attack litters in neighbouring territories. They also will start to mate with many males to reduce social stress and prevent frustrated males from killing pups.

A female bank vole carrying her blind and naked pup.

Facts

  • Scientific Name: Clethrionomys glareolusOther names: bank vole, wood vole
  • Colour: back reddish brown; sides brown or reddish brown; underparts and paws are cream;
  • Weight: Adults 15-40g
  • Body Length: 7-13cm
  • Tail: 3,5-7cm (about half of body length); top reddish brown; underside white; tufted with black hair;
  • Ears: small, but clearly visible; bigger than field voles and smaller than the ears of a house mouse;
  • Eyes: small
  • Life expectancy: in the wild up to 2 - 3 years but mostly less than a year because many fall victim to predators.
  • Droppings: black, thick, 3-6mm long

Manifestations & Damages

Overview

In huts, sheds and barns, the presence of bank voles can be detected by sounds, droppings, marks caused by gnawing and urine odours. 

Just like other rodents, bank voles destroy foodstuff, by consumption, as they eat and by contamination with saliva, urine, droppings and hair. They cause more damage by gnawing materials like paper, cardboard, insulation, packaging, textiles, cables, pipes and wood, for reasons such as opening food containers, gathering nest-building material, making access holes wider, or simply to grind down their incisor teeth. 

 

A roll of Styrofoam, stored in a barn, damaged by bank voles

In their natural environment the presence of bank voles is evidenced by holes in the ground, by their runways in the ground-covering layers of vegetation and by debarked tree branches.

Often, when a human observer remains quiet and still near a burrow, bank voles will emerge, but they will stay exposed only very briefly and will rush back into hiding at great speed.

Bank voles damage saplings and young trees by feeding on the bark of elder, beech, larch and Douglas fir trees. In years of high population density, they may cause serious reductions in reforestation and inhibit the natural regeneration of woodland. They are, therefore, regarded as plant pests.

Bank voles can be harmful to health. They harbour pathogens and parasites and bring them into human residences. Bank voles carry fleas, ticks, mites and tapeworms. Transmission of pathogens occurs by contact with the rodents’ faeces, urine, saliva, blood and hair.

Fleas leaving a bank vole that has been killed with a mouse trap.

Bank voles are the main carrier of the Puumala-Hanta virus, which causes severe haemorrhagic fever and kidney failure. The virus is transmitted by contact with an infected bank vole’s body fluids, fur or faeces. The excretions are contagious up to 12 days. Infection is also possible by inhalation of contaminated dust. This may happen when cleaning up an infested area or handling piled up firewood. The number of Hanta infections in humans correlates with the number of bank voles and every 3-4 years, when a year of high-density population occurs, there is a peak the infection rate.

Bank voles are intermediate hosts for the fox tapeworm. Humans can be infected with this worm by direct contact with bank voles, or, indirectly, via cats or dogs that have eaten bank voles. Infections with fox tapeworm are rare but disastrous. This worm ends up in the lungs, brain or liver of humans and can be fatal. There exists a treatment using powerful drugs to stop the progressive destruction of organs, but there is no cure. The drugs must be taken for life. 

When catching bank voles or working in infested areas, gloves and a FFP3 mask should be worn.

Faeces

The droppings of bank voles are a bit thicker than house mouse droppings: they are black, 3-6mm long, black, with rounded ends. An adult typically produces 50 to 75 pellets per day and even a small infestation of bank voles can produce thousands of droppings in a short time.

Gnaw Marks

Bank voles gnaw various materials. The marks caused by gnawing and the shredded materials are additional evidence for the presence of bank voles. The width of the teeth marks can distinguish bank voles from rats: a bank vole’s tooth is 0.5mm wide and a rat’s tooth 2-3mm.

Outdoors, signs of gnawing can be found on the debarked branches of elder, beech, larch and Douglas fir trees.

Sounds & Smells

When mice are active, they make noise by gnawing or by running around in empty spaces in ceilings or walls. Because of their nocturnal activity, these sounds can be especially annoying to the human inhabitants.

Mice do continuously lose urine  as they walk about. The smell helps them to orientate themselves in the dark. With substantial or long-lasting infestation, a strong smell will be detected. Cat and dog owners may see their pets excitedly sniffing, probing and scratching places, where mice have been.

Management and control measures

Conservation status: Bank vole populations are thought to be stable and not endangered. Bank voles are not protected in any country.

Prevention

Bank vole population will increase in conditions that allow easy access to abundant food and good protective shelter. These should be avoided.

The best time to act against bank voles is in autumn, when crops have been harvested and the cold, wet weather sets in. The pests leave their summer quarters and look for dry and warm shelter in and on buildings. It is best to catch or drive the rodents away before they become ensconced in buildings.

It is always interesting to find out how the mice came into the building. Mice need an opening of only 6mm diameter to gain entry so there are often many access points aroundthe  perimeter of a building. Mice penetrate mainly through open or poorly closing doors and gates, through basement windows, lighting shafts, air intake openings, pipe ducts, cable ducts, cooling and ventilation systems, outdoor lights, transformer stations, switch boxes and other apertures in outer walls. If possible, access points should be sealed to prevent future infestations. SWISSINNO Rodent Stop Steel Wool is a quick and easy fix to plug wall outlets, holes and cracks.

Wood mice are excellent climbers. Planted facades, wood cladding and insulation offer ideal climbing aids. 

Eliminate nesting possibilities to discourage bank voles from colonising the site. Get rid of piles of wood stacked against house walls, and of bulky rubbish on the site, and of dense ground-covering vegetation to make the area unattractive for nesting. 

Remove all food sources and avoid excessive bird feeding. Store foodstuffs, pet food and seeds in rodent-proof containers and not in bags or boxes.

Remedies: outdoors, agriculture, forestry:

  • encourage predators
  • set up bird perches to attract birds of prey
  • cover saplings with protective sheets
  • set up a ‘vole-free’ area by surrounding it with a protective fence and/or a trench at least 45cm deep to create an impassable barrier and then eliminate using traps all bank voles remaining in the enclosed area.

Ultrasonic Repellents

Ultrasonic Rodent Repellents are an effective method of scaring bank voles away and preventing them from entering buildings. High-pitched frequency sound waves emit a non-repetitive pattern to prevent rodents from habituating to the sound.

It is important to note that ultrasonic frequencies do not travel through walls, so at least one repellermust be placed in each room.

Ultrasonic repellers are not completely effective on their own. For maximum control they should be incorporated into an integrated pest management strategy comprising mechanical traps with food deprivation, sanitation and the closure of access routes. 

Trapping

There are no special traps for bank voles, but conventional mousetraps work perfectly well. Traps are an effective method of non-toxic and humane mouse control. There are 3 types of mouse traps commonly used for rodent control: Snap Traps, Catch Alive Traps, and Electronic Traps.

The following table gives an overview of the different SWISSINNO mousetraps:

A SWISSINNO mousetrap provides a quick and easy solution to a rodent control problem and it can be used many times over. A big advantage of using a mousetrap is that it retains the animal’s carcass so that the ‘trapper’ can dispose of it safely. Death by poison is never instantaneous so the animal may leave the scene and die out of sight in an inaccessible place like behind the skirting boards or under the floor boards where it will decompose emitting noxious odours and attracting flies, maggots and other insects into the home.

Bank voles and common voles are not trap-shy. Trapping follows the same procedure and uses the same SWISSINNO baits as for trapping house mice and wood mice.

Mouse trapping: How to go about it:

  • Before setting out traps, clean up the area removing all tracks, faeces and urine. This will disturb and disorientate the mice and make them less suspicious of the traps. It also helps to see were latest rodent activities took place.
  • Remove all food and food sources. The hungrier the mice, the more readily they will accept the traps.
  • Mice learn quickly from trap failures.  A bad trap often does not make a complete catch but injures the animal and causes it to suffer and to become trap-shy.  Only high-quality traps like SWISSINNO mousetraps are effective and suitable for animal welfare. 
  • Always check traps for proper function before use, especially for sensitive triggering and good spring tension. Don´t use traps that don’t set correctly or that fail to snap shut properly.
  • Wear gloves during trapping. That’s not because of the smell of humans. Rodents in and around buildings are not shy about humans´ smell. The use of gloves is recommended for hygienic reasons as rodents, dead or alive, can transmit serious diseases via contact with their fur or body fluids.
  • Good trap placement is the key to successful trapping. Set traps in areas of high rodent activity. Traps should be placed in the runways of the rodents. Mouse droppings and smear marks are good indicators. Traps are set best along walls or in corners and not in the middle of the room.

    Optimal placement of the trap into a runway
  • Traps must sit firmly on the ground. Rodents shy off from traps that move or make sounds when touched. A secure position is also important for a clean strike and preventing failures.

    Trap set on a board to give a good standing and fixed with a wire so it can't be dragged away.
  • It is better to set out more than a single trap, even if you think, that there is only one mouse present. If there are more mice, several traps should be set out anyways. The distance between traps should be no more than 5m.
  • If pets have access to the trapping sites, or when setting traps outdoors, the traps should be covered or placed in trap tunnels. This keeps non-targeted animals  off the traps.  The Mousetrap “No See-No-Touch” with its integrated tunnel is safe and does not need additional cover. The Mousetrap PRO SuperCat with patented trigger system is selective and helps avoid killing non targeted animals.



    Traps set in a box to keep away non targeted animals and prevent trap loss.
  • Traps should be secured with a wire or cord to prevent loss. Caught mice can carry away the trap before they die. Outdoors predators often carry away caught rodents together with trap.
  • Set traps must be checked daily. Carcasses should be disposed of before they become a hygiene problem. In case of an incomplete catch foul catch (not lethal) the animal must be dispatched. Traps that have been ignored should be moved to a different pposition. If needed, traps should be rebaited respectively reset. Non-targeted animals should be released, provided that they are not injured.
  • If traps are found tripped but empty. (failed catches), it is recommended to switch to a different model of trap. The best trap for mice is the Mousetrap PRO SuperCat. With this model, no failures or imperfect catches occur.
  • Most SWISSINNO Mousetraps are baited with peanut butter. Replacement bait syringes are available separately. The range of attractive of this bait is not more than 2 meters and rodents will not be lured from further away or from the exterior of the building.
  • “Prebait”: If a trap is being ignored, placing a small amount of bait, no more than pea-size, in front of the trap may help.

    Mouse trap with small portion of peanut butter as “prebait”
  • If the peanut butter baited traps do not work, try a chocolate spread like Nutella instead. Nutella is an excellent alternative.
  • The smell of a dead mouse from previous catch does not repel mice. In fact, used traps are more attractive to them. If traps need to be cleaned, use warm water only with a soft brush and not detergent.
  • Catch alive traps should be checked every 4 hours. Otherwise the stress can kill the captive rodent. Caught live mice must be released at least 2 km away, otherwise they will find their way back. 
  • If there is evidence of the presence of species which are protected by law, it is recommended to contact local authorities before starting control measures. Already active measures would have to be stopped immediately until approved. Even the use of “catch alive” traps without authorisation represents an infringement.

Poison bait

It is better to fight mice with traps. SWISSINNO advises against the use of poison bait for several reasons:

  • Toxic baits endanger the environment, children, pets, domestic, farm and other non-target animals.
  • Poison baits cause slow and painful death of rodents. After consuming such bait, it takes several days for the animal to die.
  • When using poison bait indoors, the mice often die in inaccessible places and the dead bodies cannot be disposed of. They decompose and give off strong, unpleasant odours that last for weeks. Later the dried-up carcasses serve for years as food for other pests such as flies, moths, and beetles.

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