Flies infesting Kotagiri, Coonoor not the harmful ‘black flies’: researchers

A team of wildlife biologists investigated recent reports of flies swarming parts of Kotagiri and Coonoor towns in The Nilgiris, to ascertain if the flies seen in the areas were harmful to humans. The researchers have concluded that the flies belong to a family known as Sciaridae, commonly known as dark-winged fungus gnats, and do not pose a threat to human health.

Speaking to The Hindu, N. Moinudheen, an independent wildlife biologist working in The Nilgiris said media reports had incorrectly identified the flies in Kotagiri and Coonoor as “black flies” or buffalo gnats, which are known to negatively impact human health in certain parts of the world.

What are black-winged fungus gnats?

“This fly seen in Coonoor and Kotagiri belongs to the Sciaridae family, commonly known as black-winged fungus gnats. They are frequently found in damp soil and greenhouses, with peak egg-laying activity occurring during the monsoon and summer seasons. Their larvae feed on roots and can damage young seedlings in commercial crops.

These flies pose no threat to humans; they do not bite, sting, or inject venom. Their life cycle lasts between 21 and 28 days, during which they lay 100 to 200 tiny eggs. They typically lay their eggs in damp soil and decaying organic matter. The adult flies feed primarily on nectar and are harmless; however, their larvae inhabit damp, organic-rich compost. These larvae are commonly found in fungi, decaying organic matter, commercial mushroom farms, and greenhouse plants. They are a notorious and costly pest in the commercial mushroom industry,” they said.

The researchers, wildlife conservationists and NGOs including Wildlife and Nature Conservation Trust (WNCT) and Ongil Nature Trust took part in the investigations which included members Arockianathan Samson, A. Abinesh, Azad Kamil, Sadiq Ali, N. Moinudheen, Mohammed Shahir and E. Vignesh who had set out to identify the species of flies that were being seen in the Nilgiris’ lower altitude towns of Coonoor and Kotagiri.

They said that the flies have natural predators in rove beetles that prey on the fungus gnats’ larvae but that these beetles are declining in areas due to heavy pesticide usage, while predatory mites also prey on the flies.

The team visited one of the areas affected on Monday (July 20, 2026) in Selas near Coonoor. They said they noticed the flies were more prevalent around water sources, and despite the local civic body conducting fumigation operations, that they proved to be ineffective, with the flies returning.

Businesses affected

Since last week, local residents around Coonoor and Kotagiri have been complaining of the fly infestation, stating that the flies are causing irritation to their eyes, while economic activity has also been affected, especially at eateries and restaurants.

Control measures

The researchers recommended measures that can be taken to control the infestation. “These flies do not pose a direct threat to humans, though they are common during this season. To control them, identify the breeding sources: look for moist or damp areas that support fungal growth, moist potting medium, water leaks in walls, and voids.

Infestations often originate from contaminated potting soil. Sciarids reproduce rapidly, making complete eradication difficult,” they said.

They also appealed to the public not to spread panic about the flies, urging scientific intervention from the local civic bodies and district administration to control the problem.