India's bristle worms are often overlooked. But they are crucial to the health of the country's wetlands – which is why local women are working to catch the poachers decimating their population.

Jyothi, 40, will never forget the day she almost died. The morning started off like any other at Pulicat Lake, part of one of three important wetlands that attracts monsoon rain clouds from October to December. Located on the east coast of India, 50km (30 miles) from the city of Chennai, Pulicat Lake is an enchanting lagoon, roughly half the size of the city of London. Pink flamingos dot its sandy banks. Migratory birds flock to its many islets in their thousands, while fishermen cast their nets into the glassy waters.

On that day in May 2022, Jyothi, who goes by only one name, had set off to work by 09:00 with 10 other women. Rain had soaked the mud paths, making the way treacherously slippery, but the women were adept at navigating the rough terrain. Their job was to wade ankle-deep in the marshy waters of the lagoon's inlets, hunting for fresh fish, shrimp and crab. Two to three kilos of catch, a good day's haul, could fetch ₹500 (£5/$6.25).

As Jyothi waded into the lagoon, she felt something close over her right foot. She slipped. Her head went under. Entangled in the roots and shrubs, she couldn't surface on her own. Terrified, gulping marshy water, she only avoided drowning thanks to the other women who pulled her to safety.

After she was back on the marshy banks, she looked closely at what had caused her to slip. It was a white bucket, the width of her foot. When she had accidentally stepped into it and lost her balance, she couldn't pry it off. Now she saw why it was there: shimmering inside were squiggling, translucent pink creatures known as bristle worms, or polychaetes.

Ten species of polychaetes have been identified so far at Pulicat, all of them endemic. They are a crucial part of the lagoon's ecosystem. Among other roles, they are a main source of food for its fish and crustaceans – which feed not only humans, like those who buy catch from Jyothi, but birds and animals too.

The worms also are a prize of local poachers. Often, the poachers fix empty buckets, like the one that had caught Jyothi's foot, in the muddy floors of the shallow waters to fill with worms, collecting them later. They sell the worms as feed to the dozens of aquaculture farms, many illegal, that dot the banks of Pulicat.

"I realised at that moment that it was human greed, and not the worms itself, that almost cost me my life," Jyothi says now.

But Pulicat's worm poaching threatens other consequences for Jyothi – and for the entire area.

"Pulicat Lake is what is known as an 'ecotone' – a transition zone between two ecosystems, in this case, land and water," says soil biologist and ecologist Sultan Ahmed Ismail, one of the pioneers of worm research in India. The species that thrive in these ecotones, called "edge species", are integral to the ecosystem's wellbeing. The polychaetes are among these edge species, particularly a group of worms called nereids.

Like fish, these nereids need the dissolved oxygen in the saline waters to survive. They get this oxygen by burrowing into the soil and breathing through the surface of their bodies; some species have external gills. They eat detritus: the organic matter produced by the decomposition of other organisms and waste products that settles at the water bottom. This detritus contains dead phytoplankton, which is highly nutritious for fish, crabs and other crustaceans, says Ismail.

The fish and crustaceans rely on this detritus, which they get by consuming the worms. While it may seem........

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