Siu Lang Shui Site of Special Scientific Interest (SSSI) is a lowland area which is located at Northwest New Territories, beside Castle Peak. The SSSI used to be a landfill during the 1970s. It was closed and later restored in the 1990s. Taiwan Acacia (Acacia confusa), Ear-leaved Acacia (Acacia auriculiformis), Cadaga (Corymbia torelliana), Brisbane Box (Lophostemon confertus) and other tree species were planted at the site. The first sighting of Danainae overwintering in Siu Lang Shui SSSI was recorded in 1999. Since then, Danainae in aggregation overwintering at Siu Lang Shui SSSI has been reported every year, each time lasting for about 2 to 3 months. According to research, 32,000 to 45,000 butterflies were recorded during the winters from 2002 to 2003 in Siu Lang Shui SSSI.