Rodents

Rodents: Rats and Mice

The Rodents are a large group of mammals with over 1500 representative species worldwide. This is close to 40% of mammals consist of one group of Rodents.

Rats have lived in close association with man ever since dawn of civilization when he gave up nomadic life and settled down to farming with a roof over his head. In spite of living close to man and sharing his food and abode, rats have always remained undomesticated.

Rodents are most easily distinguished from other mammals by the characteristic arrangement and form of their teeth. They have only a single pair of incisors in both upper and lower jaws and no canines. The wide gap (diastema) between the paired incisors and the molars gives the rodent skull an unmistakable appearance.

The incisors form the clue to the tremendous success of rodents with in the animal kingdom. Rodent incisors have three basic characteristics that together distinguish them from the teeth of most other animals; they are strongly curved, they grow continuously throughout the animal’s life, and they carry a thick layer of enamel on the outer side only.

The fact that rodents’ incisors grow continuously means they must also be worn away continuously. It is often said that rodents must gnaw in order to prevent their excessive growth, but this is not necessarily true, rodents can wear away their incisors by rubbing the lower set against the upper set. This results in softer dentine wearing more rapidly than the hard enamel, giving a chisel like outer edge to the teeth. In the gnawing of rats and mice they can penetrate soft metals such as lead and aluminum.

Rats and mice are now present throughout the world. Their adaptability has enabled them to survive extremes of climate from the frozen tundra to dry arid deserts. They were amongst the first animals to be fired from the earth in rockets. They also played a major role in the development of modern medicine.

Rats and mice are collectively called as commensal rodents. The word commensal means “sharing one’s table. Rats and mice have been sharing people’s food and shelter for many years. The word rodent means “to gnaw.” Like all rodents, rats and mice possess chisel like incisor teeth which grow continuously through out their lives. These incisors are kept filed and sharp primarily by the rodents grinding the incisors against one another, and secondarily by the rodents constantly gnawing the on various objects.

There are three species of commensal rodents which are of most concerned with the pest control professional.

Types of Distribution

In India There are about 136 species of rodents are recorded, However very few about 15 to 16 species are of economic importance. These can be divided into 4 broad groups, based on their relationship with man.

Domestic rodents : Living with man and sharing his food. These rodents nest and live in human habitations.
Commensal rodents : Living on man but not with him. They prey on his food and live on refuse from man. They sometimes enter human habitations in search of food but do not remain there.
Field rodents : Living on man but away from him. These rodents live in cultivated fields and consume agricultural produce.
Wild rodents : Living without man. These rodents live in wild and in forest away from man.

Transmission of Diseases

The diseases transmitted by rodents and other animals to men are known as Zoonoses and there is a wide range on a world wide basis.

Plague

This is spread from rats and mice. Also known as Black Death. This is spread from rats to man by a Flea, Oriental rat flea, Xenopsylla cheopis. Fleas transmit plague bacterium Yersinea pestis from infected rats to man. The more recent outbreak of plague in India highlights the continuing threat presented by this disease.
The rapidly growing human population in urban areas and the frequent failure of support services such as refuse collection and sewerage disposal to keep pace with these increases, means the conditions that are conductive to rodent infestation abound: Plague is certainly not a disease of the past. Other diseases cause significant mortalities in humans, but do not attract the same publicity as plague.

Leptospirosis or Weils Disease

Salmonellosis

Food poisoning or Salmonellosis is the name given to the infection of Man by organisms of bacterial group Salmonella. Our concerns are of those types infecting Rodents which may be passed on to Man in contaminated food and liquids causing illness and even death. Rats and Mice reflect the environment in which they live and must be seen as the potentially. Rodents also feed on food contaminated bacteria, thus they will pass them on through their droppings and urine further contaminating food intended for human and cattle consumption.

Murine Typhus Fever

This is caused by richettsia typhi. Rats carry the disease organisms and rats fleas transmit this to the Man. The organism enters the Mans blood stream when faeces of infected fleas are scratched or rubbed into a flea bite or other break in the skin through injury.
The full cost of the impact caused by Rodent borne diseases is rarely identified. It is not only the mortality that need to be considered, but also the debilitation suffered by the survivors, costs of hospitalization and treatment, loss of work, etc. which needs to be borne in mind.

Rodents as economic pests

Rats and mice attack our food in the farm, orchard, live stock facilities, during its processing, storage and transports and while it is in supermarkets, restaurants and homes. And what the rats and mice don’t eat, they spoil by contaminating it with their urine, feces or fur. Experts estimate that rats and mice destroy enough food each year to feed over 200 million people.
In buildings, rodents damage doors, floors, ceilings and walls as their burrowing and gnawing activity. They also regularly gnaw on various utility pipes and electrical wirings which have resulted in explosion, indoor flooding, fires, equipment malfunctions, and power shortages.
Today’s high-tech production, rodents are capable of causing millions of monetary value in production losses due to shut down of complex computer system when they know, nest or excrete wastes inside computers and other sensitive equipment.

Commensal rodents

House mouse: Mus musculus

House mouse is identified by a small slender body weighing around 15 to 25 grams as an adult. Ears are large; tail is semi naked and is as long as the head and the body together, dark grey in colour.

Body wt. 20 - 25 Gms.
Small sized rodents
Tail equal or little longer than body
Nose pointed, slender body, ears large, prominent and thin
Brownish-grey to blackish
Climbs, gnaws, lives indoors and outdoors

Biology and reproduction

When the living conditions are very good (plenty of food, water and shelter) rodents can multiply. The female produces

Body wt. 20 - 25 Gms.
Small sized rodents
Tail equal or little longer than body
Nose pointed, slender body, ears large, prominent and thin
Brownish-grey to blackish
Climbs, gnaws, lives indoors and outdoors

Bandicoot rats: Bandicota bengalensis

Bandicoots are known as field rats and have stocky body, are larger, stronger, more aggressive. This rodent is also found in fields and cause enormous damage. They have burrowing habit. In urban areas this rodent is often found near garbage dumps, railway tracks, outside buildings and apartments. Their presence is confirmed by presence of burrows around the buildings.

Body wt. 600- 750 Gms.
Medium to large sized rodents
Tail shorter than body
Blunt snout, stocky body, ears short and thick
Brown to black
Burrowing habit swims and dives easily, live indoors and outdoors in sewers and drains.

Roof rat: Rattus rattus

The roof rat is also known as the black rat, ship rat. The roof rat is appropriately named because by nature it is good climber and commonly lives above the ground in “roof” or aerial areas around structures. Their nests may be located in trees, clinging vines or on the sides of buildings and fences or inside buildings in attic area, ceiling voids. Roof rats enter buildings from the roof or by using various utility lines. If population builds up they expand their nesting areas to include underground burrows within industrial and residential landscape areas, ground floor areas inside buildings, under pile of rubbish.

Body wt. 250-300 Gms.
Medium sized rodents
Tail longer than body
Nose pointed, slender body, ears large, prominent and thin
Brownish-grey to blackish
Good climber, gnaws, often live off the ground in trees, vines, live indoors and out doors

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