Environmental group Green Power released the latest findings of the “Solar Terms Butterfly Phenological Survey” today. The butterfly count covering the whole period of past 24 solar terms starting from Spring Commences in February 2024 to Severe Cold in January 2025 recorded a total of 123 species and 6,990 butterflies in Shing Mun Country Park and Tai Po Kau Nature Reserve, two butterfly hotspots.
Matthew Sin, Chief Environmental Affairs Manager of Green Power, said the survey had been conducted for two decades since 2005. The counts showed an overall growth of butterfly population despite occasional ups and downs. Juxtaposition of the first (in 2005) and the latest (in 2024) butterfly count shows a 20-year increase of 7% by species and 50% by tally count.
Matthew said the past twenty yearly counts recorded between 110 and 128 species of butterflies, an average annual increase of 0.6 species, and the tally count fell between 3,900 and 7,800, an average increase of 70 per year. The numbers are a heartening sign of growing butterfly resources in Hong Kong.
Cyclical Fluctuation in Species Richness
Matthew pointed out that an annual cyclical fluctuation in species richness had been observed over a span of twenty years. The number of butterfly species rebounds from Spring Commences in early February every year and reaches peak during Summer Solstice in late June. It then goes downhill but climbs to another peak during Frost in late October before it falls to the annual lows during Spring Commences. The ebb and flow of the species richness repeats each year.
Matthew remarked that the coldest days in Hong Kong were usually recorded during Spring Commences when most of butterflies were eggs or pupae, hence the lowest number of butterfly species. When it warms up enough for leafing to start and flowers to bloom, butterflies thrive and peak during Summer Solstice. Species richness declines when it gets hot at the beginning of typhoon season and climbs up again when stable weather resumes in October. The climb reaches a smaller height during Frost before it descends when temperature drops.
New Butterfly Species Set Up Home
New butterfly species have been spotted in Hong Kong from time to time. Some visited occasionally but some stay. Matthew said species such as Common Archduke (Lexias pardalis), Tailless Line Blue (Prosotas dubiosa), Common Line Blue (Prosotas nora) and Fluffy Tit (Zeltus amasa) had been documented regularly in the survey since they made their first appearances. He believes these tropical butterflies have set up home in Hong Kong according to the survey which indicates as Hong Kong warms and food plants for these butterfly larvae exist in country parks they have adapted to local climate and ecosystem.
About Solar Terms Butterfly Phenological Survey
Green Power launched the first of its kind Solar Terms Butterfly Phenological Survey in 2005. The survey covers Shing Mun Country Park and Tai Po Kau Nature Reserve and collects butterfly data in the long term for analysis and comparison. The butterfly survey is carried out during the solar terms to record the number of butterfly species and investigate any changes and correlation.
