The Golden Birdwing (Troides aeacus) is a rare butterfly that is only known from a few localities in Hong Kong. With black and yellow accented wings and a wingspan of up to 16 cm, it can look like a small bird from a distance. Its striking appearance has made it attractive not only to wildlife lovers, but also to poachers, causing numbers to drop. On top of that, the caterpillars are fussy eaters that feed only on the leaves and young shoots of India Birthwort (Aristolochia tagala), which has a very narrow distribution in Hong Kong. For these reasons, the Golden Birdwing is a very rare sight.

Our horticulturalists began cultivating A. tagala in our nurseries several years ago and plant them out on our forest restoration site in 2019. Then, for the first time this year, we observed a handful of caterpillars feeding on the leaves! Though we fear for the survival of our young A. tagala plants, bringing back this extraordinary animal is a worthy outcome in itself.

The caterpillars are gigantic, attaining up to 15 cm in length, and they are adorned with enormous bright orange and black bristles to warn predators of their toxic nature. This toxicity is accounted for by their diet of A. tagala leaves, which contain carcinogenic Aristolochic acids. To further protect themselves, the caterpillars poke out a snake tongue-like structure and omit a foul odour to deter predators when agitated.

By providing a food source for this rare fussy eater, KFBG’s botanists have successfully lured the female butterflies to lay their eggs on the host plants and rear a new generation of caterpillars. We hope that this will support the growth of a new population of Golden Birdwings at KFBG this summer!