What are danaid butterflies?
The danaid butterflies are a group of ~300 species in the subfamily Danainae whose larvae feed on toxic plants in the family Apocynaceae. They are also known as the "milkweed butterflies."
Because their larvae consume toxic plants during their development, sometimes these toxins are retained in the bodies of adult butterflies. This makes them unpalatable to predators.
To warn potential predators of their toxicity, danaids have evolved warning coloration. The wings of these species are conspicuously colored – often striped with bright orange, black, or blue, leading to common like "tiger."
What are some examples of danaid butterflies?
The monarch butterfly (Danaus plexippus) of North America is the most well-known danaid. Asian examples include the Common Tiger (Danaus genutia), the Blue Tiger (Tirumala limniace), and the Blue-spotted Crow (Euploea midamus) – all of which are present in Hong Kong (at left).
How are danaid butterflies special ecologically?
Many danaid butterflies migrate! Migration is the persistent movement of members of a species from a region with less suitable seasonal conditions to one of more suitable conditions. The most well-known migration among danaids is that of the monarch butterfly in North America (left).
Migration is a spectacular phenomenon, but it considered by some scientists to be an endangered one due to habitat loss, declining population sizes, and climate change.
Migration in danaid butterflies
I've heard that monarchs migrate, but why?
The monarch butterfly migration is considered one of the most spectacular natural phenomena in the world.
Monarchs breed all over North America in the summer months, but they must escape the cold winter temperatures in order to survive to the following spring. Each autumn, millions of adults fly to the fir forests of central Mexico.
In these forests, monarchs roost together, forming clusters of hundreds of thousands of butterflies. Clustering helps them keep them warm throughout the winter.
Before departing Mexico in the spring, the butterflies mate. As they return northward, they produce new generations. These new generations complete the northward migration, which is remarkable, as they have never made the journey before.
The migratory monarch was recently classified as endangered by the IUCN due to severe declines in population size.
Do other danaid butterflies migrate?
Yes! Danaid butterflies are known to migrate in some parts of Asia. In Hong Kong, danaids spend a portion of each winter in clusters similar to those of the monarchs. However, we do not yet know the extent of their migration. Finding out is the goal of our research!
In Taiwan, four species of Euploea butterflies move annually from northern parts of the island to forested valleys in southern Taiwan, forming clusters of thousands of individuals in winter, similar to those formed in Mexico.
The Chestnut Tiger (Parantica sita) is known to migrate between Taiwan, Japan, and Korea. The longest recorded flight was from Japan to Hong Kong (Kanazawa et al., 2015) – a distance of at least 2400km!
Danaids in Hong Kong
What migrating danaid butterflies are found in Hong Kong?
Danaids form in clusters in Hong Kong's forests in late November to December. These clusters can consist of thousands of butterflies of various species.
Two species dominate these clusters: the Blue-spotted Crow (E. midamus) and Common Crow (E. core), usually accounting for over 90% of individuals.
Other common species include the Ceylon Blue Glassy Tiger (Ideopsis similis), Blue Tiger (Tirumala limniace), Dark Blue Tiger (T. septentrionis), Common Tiger (Danaus genutia), Glassy Tiger (Parantica aglea), and Striped Blue Crow (E. mulciber).
It is remarkable that danaids in Hong Kong are still engaged in seasonal movement and winter clustering, given the high human population density and degree of urbanization. We want to learn as much as we can about their ecology while their populations still persist.
What do we know about danaid migration here?
While clusters of danaids have been observed for years, the origin, destination, and route of their migrations are not well understood.
In 2002, AFCD conducted the first mark-release-recapture study to assess the seasonal movement of Hong Kong's danaids. Two Euploea butterflies were observed to fly from Shing Mun to Siu Lang Shui, Tuen Mun (westward) (Wong et al., 2004).
Yiu (2009) speculates that danaids may migrate through Hong Kong to some outlying islands in Guangdong and Hainan, based on the temporal pattern of winter clusters in southern China.
Our research is aimed at understanding danaid movement throughout this region.