Rare butterfly sets up home in Hong Kong’s Fung Yuen reserve
Tai Po group says relatively new species may have migrated from nearby Sha Lo Tung amid environmental damage
The Tai Po Environmental Association, which manages the two- hectare reserve, believes the acraea issoria, or yellow coster, could be migrating from Sha Lo Tung – a nearby rural enclave recently subject to a major change in environmental conditions and land use.
Regular surveys by the group between June and July this year found the yellow coster was not just making rare appearances in the reserve, but was now breeding there too.
“We would see adult yellow coster butterflies before but now we have also found their larva, including caterpillars,” said association director Dr Yau Wing-kwong.
“If there is environmental change, it is natural that they will want to move house ... They are now the new residents of Fung Yuen.”
First recorded in Wu Kau Tang in 2002, the slow-flying yellow coster is classified by the Agriculture, Fisheries and Conservation Department as “rare”.
It is distinguished by its leathery orange wings with black marks and its release of a foul, toxic liquid when disturbed.
Populations have been found in Tai Lam Au, A Ma Wat, Hok Tau, Chuen Long and Sha Lo Tung, where ramie plants grow and are a source of food for their caterpillars. For that reason, its name in Chinese translates to the “ramie butterfly”.
Fung Yuen project officer Gary Chan Ka-wang said the sudden arrival of a non-native species may have caused the yellow coster to migrate. “A lot of the ramie in Sha Lo Tung have now gone, replaced by a non-native species,” he said.
The group’s latest annual study of the city’s top 10 butterfly hot spots – which include Fung Yuen – lists Sha Lo Tung and Tuen Mun’s Lung Kwu Tan as subject to the highest level of destruction.
In August, soil fill was dumped over a 1.25-hectare wetland once covered in dense vegetation less than 200 metres from a site of special scientific interest and an important butterfly habitat. The Conservancy Association called for proper land-use controls and zoning to be introduced.
Yau admitted that degradation of private land near or within conservation areas would continue to threaten butterflies. He urged the government to establish a land trust to give owners financial incentives to conserve their land.
