Environmental group Green Power released the latest findings of its "Solar Terms Butterfly Phenological Survey". The survey took place at two butterfly hotspots including Shing Mun Country Park and Tai Po Kau Nature Reserve, and it begins with the first solar term of each year ("Spring Commences" in February of New Calendar), and runs through to the last solar term of next year ("Severe Cold" in January). The latest survey covered 24 solar terms of 2025 (from "Spring Commences" in February 2025 to "Severe Cold" in January 2026), recording a total of 124 butterfly species and a tally count of 5,645 individuals. Compared to previous year's survey, the number of species slightly increased by 0.8%, while the total number of individuals dropped by nearly 20%.
Lo Wing-fung, Environmental Affairs Manager of Green Power, noted that the number of butterfly species has hovered around 120 in recent years with little fluctuation. However, the total number of individuals has shown significant volatility, and is easily affected by particular species in a given year. For example, during the massive outbreak of the Red-base Jezebel (Delias pasithoe) in 2023, the surge in numbers for this species alone caused the total number of individuals for that year to jump by 37%.
However, Lo pointed out that compared to the overall number of species and individuals, fluctuations in the count of individual species deserve far greater attention. He noted that since the survey began in 2005, the sightings for many butterfly species have exhibited a downward trend. Among them, four species showed notably sharper declines. This includes the rare Muirhead's Labyrinth (Neope muirheadii) and the uncommon Constable (Dichorragia nesimachus). Both species were recorded every year during the first decade of the survey, averaging 2.9 and 2.3 sightings per year respectively. However, in the subsequent ten years of monitoring, both species were recorded in only six of those years, with a 70 % decline in average annual sightings to 0.8 and 0.7 times respectively.
Furthermore, the uncommon Lesser Forest Blue (Taraka hamada) and Shan Nawab (Polyura nepenthes) were recorded in nine and eight years respectively out of the first ten years, with average annual sightings of 2 and 1.8 times. Yet, during the following decade, both were recorded in only four out of the ten years, with average annual sightings dropping to just 0.4 and 0.5 times respectively. Furthermore, the average annual sightings of Lesser Forest Blue plummeted by 80%.
Lo stated that although the total number of butterfly species recorded in the "Solar Terms Butterfly Phenological Survey" over the past two decades has remained stable at around 120, the historical records of these four species suggest that the populations of certain butterflies may be shrinking, leading to fewer records each year. He explained that this trend may be linked to changes in plant communities and the distribution of larval food plants, or influenced by the intensifying impacts of climate change in recent years, requiring continued long-term monitoring.
