About 136 species of rodents have been recorded in India; however, only 15 to 16 of them are of economic importance. These can be divided into four broad groups based on their relationship with man:
Domestic rodents: Such species nest and live in human habitations and share human food.
Commensal rodents: These live on human food but not with them. They prey on refuse. Sometimes they enter human habitations in search of food but do not remain there.
Field rodents: These rodents live in cultivated fields and consume agricultural produce.
Wild rodents: Such rodents live in wild and in forest away from man.
Whatever the kind of rodent, we need to be concerned as they can cause
- Damage to the agricultural crops
- Damage and contamination of stored and processed food
- Transmission of diseases
- Structural damage
- Fear (rodent phobia)
Damage and contamination of stored and processed food
Commensal rodents also eat the food we like, both processed and unprocessed. Therefore, wherever food is stored, processed or served, rodents are likely to be present. They not only eat food, but also contaminate larger amount of food with their droppings, urine and hair. Rodent infestation is very common at warehouses, shops, supermarkets, factories and offices.
Structural Damage
Damage to structures by gnawing is very common and widespread. The enamel of the outer surface of rat’s incisors is very hard and can attack any kind of material. Lead pipes and metal sheathed cables are sometimes gnawed through, causing interruption to services. Same is applicable to optic fibre cables and communication line network. They also damage structures and drainage systems by their burrowing activty.
Rodents frequently damage electrical wiring, causing electrical failures and fires due to short circuits. No reliable data is available but it is considered that majority of the fires are caused by short circuit resulting from rat damage.
Transmission of Diseases
The diseases transmitted by rodents and other animals to men are known as Zoonoses. These include Plague, Leptospirosis or Weils Disease, Salmonellosis (Food poisoning) and Murine Typhus Fever (rickettsial).
Rodent Management Programme
For the success of the rodent management programme, firstly it is important to restrict access and availability of food, water and living space for rodents; thus reducing the likelihood of successful colony development. Secondly, in any control programme, operators must ensure 100% elimination of rodents from the given premises; thus removing the potential for the development of new generations from survivors of the control operations.
Commensal rodents, being nocturnal, have acquired a wide range of sensory skills combined with their physical abilities making them highly adaptable to take advantage of any opportunity in their environment. They are not always nocturnal and may, in certain circumstances, be active during the day. They should never be physically underestimated. They are strong, fit and exhibit inclination to explore and penetrate new areas.
Rodents are able to gnaw through any material that is softer than the enamel on their incisors.
Bandicoots and Norway Rats are very good diggers and can burrow in the soil as deep as one feet, but the distances can be very long averaging 5-10ft with multiple openings. The ability of rodents to climb and use the three dimensional nature of many habitats is frequently overlooked when surveying and inspecting infestation. Roof rats are the best of four species as far as climbing is concerned and is most likely to be found in the top of the buildings.
Rodents are good swimmers, especially Norway rats and bandicoots.
All the species mentioned are omnivorous and capable of feeding on wide range of foods. Adult rats eat about 20-25gm of dry food a day and mice 3-4gm. In general, rats have rather more regular feeding habits than mice and they have a greater tendency to hold the food and eat it under cover.
Rodent Control Inspection
Object of Inspection: Before undertaking any control measures, a thorough inspection should be carried out in and around the premises that has to be treated. The object of this inspection is to identify the species and assess the size and extent of the Rodent population. This information helps in achieving good control and arriving at proper and complete proofing measures to prevent entry and movement.
Clues: There are many clues to look for when inspecting for rodents. When you find them ask yourself the following questions:
- Droppings –
What is their shape and size?
This will determine the species.
Are they soft and glistening?
This will tell you how fresh they are and whether live rodents are still present.
- Tracks –
What is the size and appearance of foot prints?
Mouse foot prints are small. Those of Roof Rats are larger. Norway rats tend to walk on the pads of their feet whereas roof rats walk on their toes.
- Smears –
Rodents always move along with vertical objects since they feel it more secure. During the process of movement they leave behind blackish grease marks on the wall or area where their body comes in contact with.
- Burrows –
Bandicoots are the expert burrowing rodents. All the burrows may not have rats since burrowing is a continuous activity and there may be lot of unoccupied or dead burrows.
- Damage –
This may be of two types – the gnawing marks – these are mostly restricted to wooden, plastic or soft metals such as lead and aluminium. The chewed material is discarded by the rats and from the freshness and teeth marks the species can be identified
- Live Rodents –
If you see live rodents during the day then either they are short of food or there is heavy infestation. It is very common to see mice moving boldly during day time without any fear. They even cross the room diagonally.
- Locating the Infestation –
Bandicoots and Norway rats are active burrowers but less efficient climbers than roof rats and mice. Their burrows which average around 8-10cm in diameter often comprise a complicated tunnel system with several exit points. They are typically found around buildings, in between buildings, near garbage bins, near vegetation comprising garden as well as weed undergrowth.
Rodent Control
The techniques available can be grouped under the following headings:
- Rodenticides (chemicals)
- Traps
- Fumigation
Rodenticides can be divided into two groups: Acute Rodenticides and Chronic Rodenticides
Rodenticide Formulations
Edible baits: The most common method of ensuring that a rodent ingests a lethal dose of a rodenticide is to add it to attractive edible baits that the rodents will eat. There is no standard bait that will always be eaten by rats and mice. Their preferences differ widely, often preferring a food to which they have already been exposed to and are familiar with.
Water Baits: Commensal rodents, particularly rats, need a free water source for drinking. This need can be exploited by adding soluble anticoagulant to water and using this as liquid baiting point. However, not all are available in a soluble form.
Contact Rodenticide: (Dusts, Gel, grease and wax)
These formulations use the habitual grooming behaviour of rodents to ingest rodenticide. The formulation, be it dust, gel, grease or wax is mixed with the rodenticide and placed in the runway of rodents so that the animals come into contact with it and get the substance on their feet and fur. Subsequent grooming by the rodent leads to ingestion of the rodenticide.
Traps
Commensal rodents can be caught either in live traps or in killing traps which are available in various designs, sizes and shapes. Some are capable of catching multiple numbers without killing them and some can catch single rat either dead or alive.
Traps are useful in situations where rodenticides cannot be used.
The use of traps is labour-intensive and expensive. Whilst these traps can kill large numbers of rodents, particularly if used very intensively, they are unlikely to lead to elimination of the rodent population unless it is very small.
The glue boards must be used indoors preferably in the bait boxes to avoid accumulation of dust and from becoming ineffective. They must be used on rodent runways or pathways to be effective.
L.P. Naik Technical Advisor Bayer Environmental Science
