An extremely rare butterfly that has not been seen in the city for eight years was spotted in a reserve in Tai Po last month.
The Fung Yuen Butterfly Reserve was the location for what was only the third sighting of the silver forget-me-not butterfly recorded in the city.
It was first spotted in October 1967 in Southern District. The second time, after 38 years, was in Sha Lo Wan on Lantau Island in 2005. It is categorised as a very rare butterfly by the Agriculture, Fisheries and Conservation Department.
"[Silver forget-me-nots] exist in Hong Kong, but there's only a few of them. We see it only when there's a sudden rise in numbers," said Pun Sui-fai, adviser to the Fung Yuen Butterfly Reserve, which is managed by the Environmental Association.
The association announced the rare sighting yesterday during the reserve's annual butterfly festival, which drew hundreds of butterfly enthusiasts.
But while it's good news for now, a nearby development threatens to drive away some of the more than 200 species of butterfly which frequent the reserve.
Mont Vert, a Cheung Kong project that will see more than 1,000 luxury flats built in its first phase, is just 50 metres away. The first phase is expected to be completed early next year.
"The 50-metre distance is not enough to act as a buffer zone to protect the butterflies in the reserve," said Pun.
"But the property developer bought the land years before we set up the reserve, so the only thing we can do is to educate the residents to minimise the impact on the butterfly habitat when they move in," he said.
Pun said shadows cast by the tower blocks would reduce the amount of sunlight plants would get, which would change their growth patterns. Fewer plants would mean a smaller butterfly habitat. "Butterflies are very sensitive to environmental changes," Pun said.
The association said the number of butterflies in the reserve had declined since construction of the project began in 2009.
Hong Kong is home to some 236 butterfly species, which are categories within five families.