Krishnan plugs two nearby holes - escape routes - with dirt. All eyes swivel in his direction as he gingerly walks towards the burrow. Using a hand crank, which looks more like a hockey puck, attached to a cylindrical device, he pours a torrent of smoke into the burrow.

Seconds later, from the acrid grey pall, Krishnan pulls out a big, brown, mangy rat. Krishnan, 41, belongs to the Irula community - who are adivasis or tribals, believed to be descendants of gypsies. Rat catching has for centuries been their primary occupation.

Irulas, a Tamil name meaning 'people of darkness' - because of their dark complexion - earn their livelihood from farmers who pay them to get rid of these vermin that can whittle away as much as a quarter of their produce.

Irulas, who sit on the bottom rung of India's Hindu caste hierarchy, are looked down upon socially. A disenfranchised community of 3 million people, they are extremely poor, and have often found themselves on the brink of starvation.

However, a few years ago, the intervention of modern technology changed their fortunes considerably. A new rat trap has made their work more productive, tripling their catch in less than half the time.

For ages, Irulas have relied on a traditional fumigation technique - rats are caught by lighting a fire in a clay pot that covers the entrance to a burrow. As air is blown by mouth through a small hole at the bottom of the pot, smoke is forced into the hideaway. The rats die of asphyxiation. But this method is successful less than half the time, and the average rat catcher makes a paltry US$1 per day. Also, the work is hazardous. Aside from running the risk of being severely burned, Irulas suffered the side effects of smoke inhalation - respiratory and cardiac illnesses. Irulas are believed to have a life expectancy of 45 years.

However, a Chennai-based NGO called the Centre for the Development of Disadvantaged People (CDDP), introduced a device which improved efficiency to 95 per cent and eliminated all health hazards. In 2004, with the help of a mechanical engineer, they designed a steel smoker attached to a hand-operated air pump, which eliminates the need to blow air by mouth and prevents burn injuries. A crank eliminates smoke.

The improved fumigator has been a boon to Irulas.

As incomes have tripled, they have been able to send their children to school. The literacy rate of this community is currently 1 per cent. More significantly, this technical innovation has brought a sense of pride to a people destined to remain wretched all their lives. 'Everyone wants to abandon their lives as rat catchers - a miserable existence that only brings shame,' says Krishnan. 'But this rat trap gives a sense of hope to our community that we, too, can have productive lives.'

Siri Terjesen of the Neeley School of Business at Texas Christian University in Fort Worth, who visited the Irulas this year, was impressed. 'The Irulas are a great example of how bringing technology to the rural poor can help them improve their lives one step at a time,' she says.

In December 2003, Sethu Sethunarayanan, the director of CDDP, presented the fumigator to the World Bank, and received a grant for US$98,500. The funding enabled him to provide these devices free to more than 4,000 families across Tamil Nadu.

But the demand is enormous. There are an estimated 3 million Irulas in India, including 150,000 in Tamil Nadu and 250,000 in the bordering state of Andhra Pradesh, and Mr Sethunarayanan's ambition is to provide the new smokers to the entire Irula community.

Although the fumigators cost a mere US$25, they are still beyond the means of the majority of Irulas, who live far below the poverty line.

'Through microcredit,' Mr Sethunarayanan says, 'these rats traps will be made available to all in coming years.'

With more than 100 million small farmers in the Tamil Nadu and Andhra Pradesh states seeking the Irula rat catchers' help, the fumigator is in demand.

Rats - a nightmare for farmers - breed all year around, multiplying at a frightening pace. Each female produces up to 1,000 offspring in her lifetime. As crops mature, swarms of rats decimate the harvest.

'By one estimate, if the entire rat menace were alleviated, India would be able to feed its entire population thrice a day,' says Dr Terjesen.

Farmers around Sirigumi prefer not to use poisons to control the rats as that would impede soil productivity. The poisons are a threat to other species and to humans, and it is believed the rats quickly develop a resistance to them. The best answer, say local farmers, is a combination of traps and natural predators. Irulas fit the latter description, as well as being trappers.

The rat is the Irulas' main source of food. The rodent's carcass provides meat and any grains found in the burrow go towards making the day's single meal.

As shadows lengthen in Sirigumi, Krishnan walks home with his prized catch. He enters his tiny mud hut with a straw roof and dirt floor, the malodorous scent of the dead rats wafting in with him.

He remembers times when there was nothing but wild fruit from a bush to feed his nine children.

'My children don't go hungry these days,' he says, handing over the dead rodents to his wife. 'They feast.'