The recent survey has found a steady increase in the number of butterfly species on Pachamalai hills near Thuraiyur.
15 species were identified in 2016 and 109 in 2022, the current survey found 126 of them on the hills.
The Pachamalai hills comprise several reserve forest areas.
It covered the reserve forests of Sengattupatti extension, Kaliyamman Kovil Thittu, Solamathi, Kannimarsolai, eco-tourism park area (Top Sengattupatti) and Mangalam water falls area.
The habitat assessment covered mixed deciduous forest, riverine and secondary forest growth.
The species count of 126 has been termed a healthy butterfly population.
The hills have the potential to record 175 butterfly species.