Rodents - The Signs of Infestation

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 body gives a reasonable indication that the infestation is still active. If live animals 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, sightings are not reliable inficators of the size of an infestation.

Gnawed Materials

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Gnawed materials in certain instances reveal the time when the rodents were present. Gnawed fresh foods change their appearance within 24 hours. Wood recently gnawed presents a fresh appearance for about a week. Also, the presence of teeth marks can allow rat and mouse infestation to be distinguished.

Rats often produce distinv serrated edges while a smoother edge is produced by the smaller teeth of the mouse. Damaged grain may also give an indication. Rats tend to leave half grains, while mice nibble around the edges, leaving a core and many small pieces including grain husks. This is called "kibbling".

Droppings

This is a sign on which most imspectors rely. The shape and size of any droppings can often indicate the species that may be present. Brown rat droppings tend to be spindle-shaped and generally are grouped together, black rat droppings are on average somewhat smaller, more sausage-shaped and more scattered. Mouse droppings are much smaller. Brown rats produce about 40 droppings a day, and house mouse about 80.

If droppings are shiny and glistening this indicates an active infestation, but in dry, warm atmosphere these can become dull looking after only a few hours. The presence of small and large droppings of the same shape usually indicated a breeding population with small and large animals being present. Occasionally, other items may be confused with dorent droppings. For instance, around machinery small accumulations of grease may be mistaken for mouse droppings. Bat droppings are dark brown or blacj and vary between 4 and 8mm long, the same size or larger than a mouse dropping. Because they consist largely of fragments of insects, they cruble easily to a fine powder when pressed, whereas mouse and rat droppings are pasty when fresh and become increasingly hard as they dry.

The presence of droppings on their own, does not necessarily indicate an active infestation. Consequently, other signs should be looked for to confirm this. Before any control measures are undertaken, all droppings should be swept up and removed so that if further droppings are seen on subsequent inspections then the infestation must still be active.

Smell

Rats and mice produce characteristic "stale" odours. This can be readily recognised, especially when infestations are long standing and occupy undisturbed indoor areas. Note, however, that this odour can remain for some time after the rodents have been eliminated.

Urine Pillars

Small mounds or "urine pillars" consisting of dirt, grease, dust and urine are sometimes formed in places which are habitually used by house mice. They are indicators of a long established infestation.

Smears

Through the habitual use of particular routes or tuns dark coloured smear gradually form where the rodent, brushes against a surface leaving a dark greasy deposit. These are typically seen around harbourage entrances, up walls and steps, on pipes and along beams and girders and wherever rats and mice run. The grease is produced natually in the skin, but the marks are accentuated by the adhesion of dust and dirt. When gresh these deposits tend to be soft and easily scraped off, but they become brittle with age. When smears are thick, shiny and widely distributed they indicate a heavy infestation.

Runs

Both rats and mice tend to follow the same routes when travelling. These characteristics pathways or trails are likely to be near or under cover. Outdoors the runs of brown rats can appear as continuous depressions on grass of other low vegetation or eventually as well-worn pathways of bare, trampled earth. A well-used run, whether indoors or outdoors, will be free of debris and cobwebs.

Tracks

Indoor in dusty areas or amongst finely divided substances such as flour and outdoors in mud, the footprints of rodents can be easily seen. The size and configuration of the footprints and their location is a good indication od the species. Clear footprints will show the four toes of the forefeet and the five roes of the hind feet. The prescence of tracks may also be a clear indication that an infestation is active since old tracks will soon be eradicated by dust or water.

In some situations if is very difficult to locate where rats and mice are moving. The use of non-toxic tracking dust can be of assistance. Small patches of unscented talc, flour or china clay are laid and observed the next morning for tracks. However, the absence of tracks does not necessarily mean these is no infestation.

Long, thin marks or depressions in dusty areas or, for example, on the surface of grain indicate a tail being dragged or rested.

Harbourages and Burrows

One of the requirements for the establishment of any thriving rat or mouse colony is the availability of harbourage, either artificial or natural. The burrows of the brown rat outdoors are usually easy to recognise, and are often situated on sloping ground such as banks od the sides of ditches or beneath some form of cover such as logs or flat stones. Earth excavated from the burrow remains in a heap adjacent to the entrance. Cobwebs or vegetation growth inside the entrance to a burrow indicate that it is not currently in use. It is a useful method to fill in all burrows and note which have been re-opened the next day.