The invasion of the butterflies

The Tawny Coster, an Asian species, was first noticed in northern Australia five years ago and has been spreading southwards ever since. It has reached Townsville in the last few weeks.

I was alerted to the alien invasion by a friend in Bushland Beach who saw them a fortnight ago and asked me if I had seen any (I hadn’t). At the same time he asked Peter Valentine, a recognised expert on the region’s butterflies, about it. Peter’s reply to him was:

Well spotted … it is indeed a Tawny Coster. I have been watching them cross the continent and they arrived in Queensland last year (Weipa) then this year turned up in numbers at Georgetown, then closer to us (south of Mt Surprise) just last month and this month they have reached out to Herbert, to Kuranda and just this week to Cairns. I am sure [Cyclone] Debbie is an influence. They do seem to be in migratory mode with many individuals seen flying. In other places they have been breeding. They like Hybanthus, a widespread herb. I am confident they will be breeding around Townsville soon.

Your record is the first from the Townsville area but I am expecting lots more soon! We are looking at trying to put together a compilation of observations (in NQ) as we now have it reaching the east coast for the first time and already heading south! …

I was looking out for them after this exchange, of course, and I saw them for the first time on Cape Pallarenda on Tuesday (previous post), mainly on the grassy open hillside between the creek and the point where the “Under the Radar” trail forks off from the Shelly Cove track.

Their coloration is generally similar to the Plain Tiger or Monarch, but they are smaller than either of these, about the same size as the closely related Glasswing. I noticed that some were brighter than others, blood-orange compared to dusty orange, and when I looked them up I learned that, “The males are more deeply coloured than the females,” so both sexes were around and they may already be breeding here; I didn’t look for caterpillars, however.

Their range is expanding quite quickly. David Rentz noticed them in Cairns in late March. His blog post is worth reading in full, but the key points are:

The Tawny Coster occurs naturally in India and Sri-Lanka but it has expanded its range to include Indonesia at the rate of 200 km per year (Braby et al., 2014a). The authors further report that the expansion in Australia is even more rapid at some 315 km per year (Braby et al. 2014b). …

The presence of the Tawny Coster in Australia is most likely a natural expansion of a species. Its ability to move around may have been enhanced by forest clearing in SE Asia but it may also be enhanced by Global Climate Change, a phenomenon that is being verified by many examples such as this.

When I passed on my own sighting to Peter he said,

We are still monitoring this amazing event (once in a lifetime really) and I have records from as far south as Longreach now. It would be excellent if you could keep any information coming in. I especially want to learn of any breeding records … the females lay on Passiflora [passionfruit] species and like their close relatives, the Glasswing, they often can be found hanging around a vine. Original migrants were mainly female (the ones that came down with Debbie) but now we find that there are mainly males (probably a sign of breeding as the males hang around the food plant waiting for females to emerge from their pupa).

Please send the date and location of your first sightings to him at peter.valentine@jcu.edu.au.

References

I don’t usually list my scientific references but this is such a ‘new’ story that my readers may wish to follow it up – and besides, Peter and David, both of whom are far more expert than myself, have directed me to them:

• Braby MF, Bertelsmeier C, Sanderson C, Thistleton BM. 2014a. Spatial distribution and range expansion of the Tawny Coster butterfly, Acraea terpsicore (Linnaeus, 1758) (Lepidoptera: Nymphalidae), in South-East Asia and Australia. Insect Conservation and Diversity 7: 132-143.
• Braby MF, Thistleton BM, Neal MJ. 2014b. Host plants, biology and distribution of Acraea terpsicore (Linnaeus, 1758) (Lepidoptera: Nymphalidae): a new butterfly for northern Australia with potential invasive status. Austral Entomology 53: 288-297.
• Franklin, DC, Morrison, SC, Wilson, G, 2017. A colourful new Australian reaches Talaroo: The Tawny Coster, Acraea terpsicore. North Queensland Naturalist, Volume 47 (2017), pp. 10-13.
• Kendall, Ross. A new immigrant butterfly for Australia. Metamorphosis Australia, Issue 70 (September 2013), pp. 1, 4-6, Butterflies and Other Invertebrates Club.