How many times have pest controllers heard this question? The control of rodents is necessary to protect and preserve public health. While little may have changed over the last 60 years in the tools available for rodent control, the evaluation of the impact to the environment and non-target poisoning has become an increased industry and public concern.
An important note for pest controllers is to carefully consult rodenticide product labels as the majority are only licenced for the control of the most common pest species, namely brown rats and house mice, making control of other species ‘off-label’ and accordingly not approved. Mechanical traps and rodenticides are both fantastic tools for the control of rats and mice, though they are also indiscriminate in their efficacy. If sited or applied incorrectly they can not only kill non-target pests but also facilitate the migration of toxic active ingredients into the predatory food chain.
As a responsible manufacturer, PelGar International works alongside various organisations on local and national ‘Conservation in Partnership’ environmental campaigns. Some of these campaigns employ the use of rodenticides in order, for example, to protect ground nesting bird species from rats which will readily eat their eggs and decimate populations.
Alex Wade, PelGar’s technical manager talks us through some of the differences between a few commonly mistaken pest and non-target animals. ‘One of our most common pest species is the brown rat which has, in many parts of Europe at least, pushed the black rat to near extinction. Common identification mistakes occur between brown rats and voles, here are the key things to look out for’;
|Species||Brown Rats: Rattus norvegicus
|Bank Vole: Myodes glareolus
|Field Vole: Microtus agrestis
|Water Vole: Arvicola amphibius
|Length (excluding tail)||150-270mm||90-110mm||90-115mm||130-230mm|
|Preferred food||Brown rats are omnivorous. Cereals form the bulk of the brown rats diet, however they will happily eat anything discarded or stored for human or animal consumption.
|Vegetation and cereals.||Primarily vegetation||Vegetation|
|Description||The fur of the brown rat can range in colour but typically show a brown coat with a lighter (grey) colouration on the belly, the fur can appear to be coarse due to the presence of longer guard hairs throughout the coat. They have hairless ears and tail with a blunt nose. They range across almost all habitats although typically will live close to, but not immediately next to, areas which are frequently used by people. They are predominately active in the evenings and at night.
|The fur of the bank vole is a reddish brown with a lighter (cream/grey) belly. The nose is often more rounded than that of rats and their ears, although larger than those of most voles, are still small compared to the brown rat and can often be covered in fur. Their tail is usually only half their body length and has dark fur colour top with paler colour underneath. Habitats are usually woodlands, hedgerows and farmland but can potentially extend into gardens. They can be active both day and night.
|The fur of the field vole is a dark brown with a lighter (cream/grey) belly. Their coat is bushier than that of the bank vole. The nose is often more rounded than that of rats and their ears are almost totally covered by the coat. Their tail is very short in comparison to their body (usually only 30% of the body length) with pale coloured fur all over. Habitats are usually woodlands, hedgerows, grasslands and farmland. They can be active both day and night.
|The fur of the water vole is a uniform brown top and bottom. The nose is more rounded than that of rats with smaller, furry ears. The tail is shorter compared to their body length with fur all over. Habitats are focused almost exclusively around fresh water; female voles will also commonly use the entrance to their burrow as a latrine. They can be active both day and night.
|Droppings||15 – 20mm in length. Rounded at one end and tapered at the other. Brown/black in colour.||Droppings are rarely found outside the burrows.||6-7mm in length. Cylindrical and often green. Droppings are usually found on and around the chewed lengths of grass||8 – 12mm in length, odourless and cylindrical. Usually green in colour and found in latrines.|
|Control with rodenticide||Yes||No||No||No|
Mice on the other hand, especially with their speed, can be even harder to identify;
|Species||House Mouse: Mus musculus (domesticus)
|Yellow Necked Mouse: Apodemus flavicollis
|Wood mouse: Apodemus sylvaticus|
|Length (excluding tail)||70-100mm||95-120mm||80-90mm|
|Preferred food||House mice are omnivorous. Cereals form the bulk of their diet, however they will happily eat anything discarded or stored for human or animal consumption.||Primarily cereals and fruit with a little vegetation.||Primarily cereals and fruit with a little vegetation.|
|Description||The fur of the house mouse is a dark brown which can sometimes lighten to a greyish brown underneath. The house mouse has a pointed nose with large, round, hairless ears. The tail is usually the same length as the body and is a uniform colour and hairless. They range across all habitats but are commonly associated with living immediately alongside humans. They are primarily active at night.
|The fur of the yellow necked mouse is a red brown and unlike the house mouse there is a very clear demarcation to a creamy white belly with a prominent yellow band across the chest. The yellow necked mouse has a pointed nose but larger ears than the house mouse. The tail is usually the same length as the body and can be a darker colouration on top with sparse fur. Habitats are usually woodlands and hedgerows but will also extend into gardens.||The fur of the wood mouse is a red brown and unlike the house mouse there is a very clear demarcation to a creamy white belly. The wood mouse has a pointed nose but larger ears than the house mouse. The tail is usually the same length as the body and can have sparse fur. Habitats are usually woodlands, grasslands and hedgerows but will also extend into gardens and sometimes buildings. They are primarily active at night.|
|Droppings||6 – 7mm long. Hard when dry and do not crumble like bat droppings.||8mm long. Cylindrical with rounded ends, usually deposited at feeding sites.||Cylindrical with rounded ends, usually deposited at feeding sites.|
|Control with rodenticide||Yes||No||No|
‘In any rodent control campaign the first task should always be to carry out a survey to identify the rodent species, extent of the infestation and any non-target species in the area – including predators and scavengers which could consume poisoned or dead rodents.’ explains Alex. ‘Identifying where rodents are feeding, drinking, traveling and living will form the solid basis of any toxic or non-toxic control programme. The next step is to plan an effective campaign that will have the least environmental impact. Non-toxic control methods including the use of traps should always be considered first. If and when toxic control methods are employed the least toxic yet effective product option should be selected. Bait or traps should be placed along the routes of travel identified in the earlier survey, and should be protected from children, pets and non-target species.’
‘One step that can be taken to minimise any environmental impact is to ensure enough bait is placed, bait is regularly checked and topped up and any rodents which die outside of the burrow or nest are quickly removed and disposed of in line with label/best practice guidelines. A post treatment survey, with recommendations of how to prevent or minimise future rodent infestations will also be beneficial in the long term to both the environment and the customer’.
There are a multitude of rodent species in Europe and globally and this article just scratches the surface. If you’d like to learn more, need help with identification or an environmental risk assessment please get in touch with PelGar’s technical team, email: firstname.lastname@example.org.
This article appeared in International Pest Control, July/August 2018 volume 60:4