CATCHING rats the way Irula tribals do is not only environmentally safe but also cost-effective -- for they don't use poison or chemicals. All they need are their bare hands.

Field trials in controlling rat numbers using these methods were conducted in 1984 by the Irula Snake Catcher's Industrial Cooperative Society (ISCICS), aided by an Oxfam Trust grant. As many as 714 field trials were carried out over a three-year period between February 1988 and September 1991 to establish the cost-benefits of the method and to verify its applicability all over the country.

On the basis of these trials, a more exhaustive project, funded by the government of India's department of science and technology, was undertaken. This project was reviewed by Romulus Whitaker and S Dravidamani, both researchers who also work at the Madras Crocodile Bank.

During the field trials, most of which were conducted in the Chingleput district of Tamil Nadu, the Irula tribals caught 1,71,925 field rats and recovered more than 4.75 tonnes of grain from 96,165 burrows in a 25.5 ha area. The grain recovered from the burrows is worth about Rs 20,000, but agricultural economists calculate the Irulas saved about Rs 37 lakh worth of grain from the rats. The Irulas were employed at a daily wage of Rs 25 and the cost of transporting them to the area amounted to Rs 2,45,370. The sale of rats earned Rs 24,154 for the Irulas' Cooperative Society from zoos and wildlife farms.

When these figures were finally audited, it was found the economic benefit for the three-year, rat-catching project was nearly Rs 35 lakh. A side-benefit was that half the field rats caught were eaten by the Irulas, for whom rat meat is an important, high protein food supplement.

The ISCICS, which was set up in 1978, has successfully utilised the traditional skills of this tribe of hunters who live in Chingleput district and the cooperative is now a major supplier of snake venom for medicine. The rat-catching project concentrated on the district's rice fields, other crop fields, chicken farms, hotels and godowns.

The Irula technique of catching rats consists of digging into the burrow, smoking out the rats and netting them. Their methods vary according to the season, soil conditions, rodent and vermin species and other factors. They catch the female mole rat (Bandicota bengalensis) and its brood during the rice-growing season as this is the time the female has both a brood to care for and stored grain to feed them. It is, therefore, not likely to be tempted by poisoned bait or emerge from the burrow. As Irulas are adept at differentiating between a "live" burrow and an abandoned one, neither time nor energy is wasted.

Chemical rodenticides have made little headway in dealing with the rat problem. The widely-used rat poison, zinc phosphide, has only a one-night effectiveness and as rats are intelligent and communicative, bait-shy adults train their young to avoid traps. Chemical baits also carry an intrinsic danger: A chemical that works wonders in one area may prove to be disastrous in another, because of biological, ecological and other factors.

The magnitude of the rodent problem can be better assessed when it is realised that a rat can conceive when it is just 42 days old, have a litter in 19 days and have seven or more litters in a lifetime. A rat consumes an average of 10 grams of food a day and crop loss because of rats is estimated as high as 70 per cent. Rats account for an annual loss of more than 11 million tonnes of foodgrain in India. They are also disease-carriers and take a heavy toll in terms of the nation's health.

As there is little danger of rats becoming an endangered species, commercial incentives should be considered to spur their catching. Dried rat meal is in demand for livestock and human consumption and is especially sought after by chicken and fish farms. Rat skins, tanned by the Central Leather Research Institute in Madras, have proved quite useful in the making of small leather products. Bandicoot tails have been tanned and sent to Switzerland and Japan and a market could be developed for their collagen fibres to be used in ligament repair surgery. Wild rats are also being supplied for research and there is potential here for this to be developed into a regular industry.