Rat Control

Signs and Traces of Rats

As rodents interact and infest an area, they leave signs of their activity that help to signal their presence, indicate the size and extent of an infestation and aid in identification of the species.

The nocturnal behaviour patterns exhibited by rodents means that few are actually seen by those undertaking rodent control. It is essential that rats activity patterns are identified if control programmes are to be applied effectively. This is dependent upon identifying the rodent activity from the signs and traces that they leave behind.

Sightings

The sighting of a rodent is the surest sign of an infestation and should enable a positive identification of the species to be made. A newly dead rodent body gives a reasonable indication that the infestation is active. If live rats are seen frequently during the day, it may indicate that a large infestation is present, or that the rodents’ environment has been recently disturbed. However, rodent sightings are not very reliable indicators of the size of an infestation.

Smell

Rats produce characteristic ‘stale’ odours, which can be readily recognised, particularly, that this odour can remain for some time after the rodents have been controlled.

Droppings

The droppings of the Ship Rat, Norway Rat can usually be distinguished on the basis of their size and shape. Norway Rat droppings are on average 12 mm (1/2 inch) long and are typically described as ‘spindle shaped’ (that is, tapering to a point at one or both ends). Ship Rat droppings in comparison are rather thinner, often slightly carved and usually have rounded ends. Ship rat droppings average about 9 mm, and so are slightly smaller. House Mouse droppings are much smaller, 3 – 7 mm in length and may often be spindle shaped. Norway Rat produce about 40 droppings each day.

When fresh, Rat droppings appear soft and shiny but within a few days, depending on climatic conditions, they become hard and dull. It may be possible to recognise an active rodent infestation from the state of droppings.

Rats droppings can normally be found in any area that has been visited but in buildings they are frequently concentrated in favoured places such as the corners of rooms, on the tops of walls, and crevices between packages.

Note that bat droppings, for example in a roof space, may look very similar to House mice droppings, but usually crumble easily and contain mostly insect fragments.

Urine Pillars

Rats urine pillars are indicators of a long-established infestation.

Hairs

Rodent hairs are difficult to spot but perhaps more easily seen as a contaminant of light-coloured materials or substances such as flour. Rodent droppings contain large numbers of hairs that may be released when they break up. With use of laboratory techniques, it is possible to distinguish between the hairs of Norway Rat and that of house mice.

Runs

Rats, and to a larger extent mice, tend to follow the same roots when travelling. These characteristic pathways are likely to be near or under cover. Outdoors the runs of Norway Rats can appear as continuous depressions in grass or other low vegetation or indoors are most easily discovered along regular routes through dusty places when the surfaces will tend to have a ‘cleaned’ appearance.

Footprints and Tail Swipes

Footprints may be seen where rats and mice have moving over muddy or dusty surfaces, or through finely divided substances such as flour or chalk. Clear rodent footprints will show the four toes of the forefeet and the five toes of the hindfeet.

Long, thin marks or depressions in dusty areas or, for example, on the surface of grain indicate a rat tail being dragged or rested. These are more obvious with Rat infestations.

Smears

Through the rodent habitual use of particular routes or runs dark coloured smears gradually form where the rodent brushes against a surface and grease and dirt on the fur rubs off. These rat characteristic marks develop in buildings in such areas as around entrances to harbourages, up walls and steps, on pipes, and along beams and girders. When smears are thick, shiny and widely distributed they indicate a heavy rat infestation.

Smears are sometimes seen as rat or mice characteristic ‘loops’ beneath ceiling joists. From their appearance it is often possible to determine which rodent species made them. The loops left by the Ship Rat are broken or discontinuous, confirming the agile climbing ability of this species. In comparison the less able Norway Rat forms continuous loop smear. Loop marks can sometimes also be seen in dust.

Rats smear marks can remain long after an infestation has been cleared so they are not reliable indicators of a current infestation.

Harbourage, Burrows and Nests

The burrows of Norway Rat outdoors are usually easy to recognise, and often situated on sloping ground such as banks or the sides of ditches, or beneath some form of cover such as logs, tree roots, flat stone pavements. The rat entrance holes are generally 70 to 120 mm in diameter. Earth dug from the burrow remains in a heap adjacent to the entrance, this will be trampled if the burrow has been well used by rats. Cobwebs at the entrance to a burrow indicate that it is not currently in use.

Sometimes a neat, well-defined hole will appear in the ground with little or no heaped earth beside it. This may indicate that a rat has emerged from below ground; frequently there is a connection with a drain or sewer. This may occur when buildings are demolished, and the old drains have not been sealed effectively.

If the surface rat activity is connected to a drain it is important that this fact is identified so that control measures can be applied in the drain and the drain fault corrected.

Ship Rats usually find harbourage up in the building. Norway Rats will tend to exploit shelter in the fabric of a building such as a hollow wall. However, the possibility of a Norway Rat living in associated drains and sewers should not be overlooked.

Occasionally the remains of a rodent nest can be found indoors, usually in an undisturbed area. Any readily available materials can be used to make the rodent nest. If sacking, paper or packaging is seen to be gnawed it can often indicate that rodent nests are being made. This is an important point to note during a rodent infestation survey.