The Chocolate albatross (Appias lyncida) is a fairly common butterfly in Asia, which can be found from Sri Lanka to Borneo. There are a number of different subspecies across this vast range. I was very pleased – I am always happy to see a butterfly! – to come across this fine specimen in northern Thailand (Chiang Dao) where it was nectaring in some flower beds.
This individual was a male, and is, I think, Appias lyncida vasava, on account of having a rather thick brown band on the hindwing (uds), but I am not 100% sure! Yellow is often a warning (or aposematic) colour, but these particular butterflies are not poisonous.
This butterfly is rather variable in appearance. First of all the sexes look quite different; and then there are quite different forms at different times of the year: wet and dry season forms (together with some intermediate forms if that is not variable enough!). The forewings of the females are darker, particularly on the dorsal (upperside), as my not very good photograph (below) illustrates.
In the so-called, Wet season, the differences between the sexes becomes more pronounced, with the female being much darker: heavily marked with brownish-black markings on the dorsal surface (below, right hand side). These days, there are, I think (at least people tell me), less clear-cut differences between the seasons in countries like Thailand. Nevertheless, the wet season forms were beautifully illustrated by an British artist called John Nugent Fitch (below) in a book on the butterflies of India, by Frederic Moore, published in 1903-05. The darker markings on the wet season forms are thought to be to enable the butterflies to absorb more solar radiation, and thus heat up more quickly in inclement conditions!
There is also a lovely photograph, on the Wikipedia entry for Appias lyncida, of a pair of Chocolate albatrosses (below).
It is thought that the wet season forms of Appias lyncida, which have darkened wings, may be mimics of aposomatic Delias species, which are poisonous, or at least unpalatable (Canfield & Pierce, 2010). The wet season female Chocolate albatrosses are said to bear a significant resemblance to some darker (ups) species of Delias such as D. pasithoe (see below), and certainly their ranges overlap (Canfield & Pierce, 2010).
Whether these darker female forms of the Chocolate albatross really are part of a mimicry ring – i.e. gaining protection from predation by looking like very similar, poisonous species – remains to be definitely proven, but it is an interesting idea. The theory is that female butterflies are the ones that most need this mimicry protection. They may carry carry heavy loads of eggs, which could impair their ability to escape when attacked by birds and other predators; so natural selection will favour the ones which look like species the predators have already learned to avoid! Males on the other hand, are I suppose, more expendable! Their bright colours are probably more to do with attracting the ladies, than frightening off predators!
Quite why we find brightly coloured creatures like this, so attractive, is another, deeper, question; but let’s leave theorizing aside for now, and I hope readers will just enjoy the spectacle in the following images!
Canfield, M. R., & Pierce, N. E. (2010). Facultative mimicry? The evolutionary significance of seasonal forms in several Indo-Australian butterflies in the family Pieridae. Tropical Lepidoptera Research, 20(1), 1-7.
Lepidoptera Indica. Volume 6, Plate 540. Lovell Reeve & Co, publishers https://www.biodiversitylibrary.org/item/103503#page/207/mode/1up