This is a story of a moth, Histia flabellicornis (Zygaenidae), which is a Müllerian mimic, which means that it is an unpalatable species in the same area as other unpalatable moths and butterflies of similar ‘aposematic’ appearance; a sort of mutual resemblance society! I introduce other sorts of ‘Batesian’ mimics first, swallowtail butterflies which are not poisonous or distasteful, before turning to the interesting story of this black moth.
It is widely known that many insects such as butterflies sport warning colours to let predators know that they are poisonous, or at least, rather toxic and unpalatable. These so-called aposematic insects, are in turn the models (or templates if you will) for a host of other insects to imitate, or mimic, and thereby gain protection. This is called Batesian mimicry after Henry Walter Bates, who first discovered it. Predators, such as birds, lizards and so on, learn to associate the colourful warning signals with toxicity and reduce their attacks and consumption of these sort of aposematic prey items. It helps if the mimics are not too abundant compared to the models – which would swamp the effect of the warning colours – and occupy the same sort of habitats. Birds are smart and not fooled so easily! Many still continue to consume aposematic prey, particularly if they are very hungry. Nevertheless, once the predator – let’s call it a bird – has had a mouthful of the unpalatable butterfly (the model) this experience of distastefulness is from then on associated with the poisonous insect and by implication linked to the toxicity of the chemicals it contains. In other words, the predator effectively avoids toxic prey without having to actually eat them each time. That’s why so many butterflies – models and mimics – have beak-marks on their wings, presumably evidence of having been tasted – bitten and spat out – by the predator during the learning process!
Alfred Russell Wallace was one of the first to notice that butterflies such as the Common Rose, Pachliopta aristolochiae, and many other red-bodied swallowtails – papilionid butterflies in the genera Atrophaneura, Byasa, Losaria and Pachliopta – were unpalatable models for various Batesian mimicry complexes, particularly in the genus Papilio, which are black-bodied swallowtails. For example, two relatively common papilionids, the Great Mormon (Papilio memnon) and the Common Mormon (Papilio polytes) are Batesian mimics of, which is to say they resemble, models such as the Common Windmill, Atrophaneura polyeuctes, and Pachliopta aristolochiae (below). The situation is in practice more complicated as these mimics are highly polymorphic, and it is only certain female forms which are mimetic. For example, P. polytes (immediately below) is a very good mimic of the common rose, Atrophaneura (Pachliopta) aristolochiae (2nd photo below). It’s easy to remember that the mimics have black bodies, whilst the models are red-bodied (at least to some degree). I’m not sure why birds can’t learn this too! But it’s probably quite difficult to spot from a distance.
The red-bodied swallowtails like A. polyeuctes and P. aristolochiae are toxic because they contain pyrrolizidine alkaloids (PAs), which they have obtained by feeding (as larvae) on poisonous plants – woody vines – in the genus Aristolochia (family Aristolochiaceae). The Papilio species on the other hand, feed on more edible plants in the family Rutaceae, including many citrus species.
Another common black-bodied swallowtail, closely related to P. polytes is the Great Mormon (Papilio memnon), which has as many as 26 different female forms; some wag of a taxonomist must have thought it appropriate to name it after the polygamous Mormons. There are mimetic and non-mimetic female forms, but the dark male is always non-mimetic (see below). The mimetic females on the other hand, have tails in their hindwings and aposematic colouration on their hindwings and abdomens. Mimetic female forms of P. memnon are considered to be a mimics of Atrophaneura polyeuctes. For photos of mimetic and non-mimetic female of Papilio memnon see Fig. 1 in Komata et al., 2016, and in a wonderful series of courtship sequences, here.
There is another sort of mimicry, where unpalatable species can in effect reinforce their distastefulness by sharing the same sort of aposematic appearance; a sort of mutual resemblance society! In practice however, there may be a spectrum of relative palatabilities. (6) This is called Müllerian mimicry, after J F T (‘Fritz’) Müller, who discovered it.
I stumbled across a nice example of a Müllerian mimic in November 2017, in northern Thailand, in the form of a zygaenid moth, Histia flabellicornis (below).
This lovely, red-bodied, diurnal moth – with its striking black forewings – is found from Southeast Asia to Taiwan and Okinawa (but not on the Japanese mainland). In Okinawa, it was found to be part of a mimicry circle with butterflies and moths, the model being the Common rose. In this case however, the moth is mimetic with the male butterfly – which is black (see below) – of the Chinese windmill, Atrophaneura (=Byasa) alcinous (see reference #4: Nishida, R., 2017). The female Chinese windmill has much whiter wings (described as gray or smoky brown)(4).
Adults of Histia flabellicornis were found by Professor Ritsuo Nishida of Kyoto University, to ‘secrete toxic linamarin and hydrogen cyanide (HCN) as a foam when disturbed, suggesting the moth to be a Müllerian mimic, in alliance with A. alcinous in Okinawa (4). The fact that the moth stores cyanogenic glycosides, means that it is toxic, so it is regarded as a Müllerian (rather than a Batesean) mimic, which would be palatable. The larval host is said by Nishida (2017) to be the bishopwood tree, Bischofia javanica (Euphorbiaceae), which is presumably toxic.
Professor Ritsuo Nishida had also previously discovered that Histia flabellicornis larva (below) secrete droplets of cyanogenic fluid from special glands if they are disturbed (3). I.e. they are toxic. Predators beware!
Fascinatingly, Professor Nishida found that another black moth, Epicopeia hainesii (Epicopeiidae) (below), was also part of the mimicry ring in Okinawa (see Fig. 11.6 in Nishida, R., 2017).
So the zygaenid moth, Histia flabellicornis, is in a mimicry ring (in Japan) with another black moth, Epicopeia hainesii (Epicopeiidae) and the papilionid butterfly, A. alcinous, and the model for papilionid is surely a red-bodied swallowtail. The palatability of the aposematic moth , E. hainesii, is unknown, but it is probably unpalatable (4). I have taken the liberty of copying the figure below, from this open access publication.
The Chinese Windmill (A. alcinous) is not, as far as I am as aware, present in Thailand, so perhaps the zygaenid moth (Histia flabellicornis) is part of a different mimicry ring there? If it is not a Batesian mimic, and has its own defensive chemicals, it does not need the presence of a poisonous model to avoid predation. But Professor Nishida cautions that the quantity and quality of defensive chemicals can vary from plce to place, so that ‘Batesian and Müllerian mimicries may be interchangeable’ (4). So perhaps this moth fits into Müllerian or Batesian mimicry circles with whatever poisonous models are present in the area and we should be cautious about assuming that if it is a Müllerian mimic in one region it will also be in another area.
I took these photographs of Histia flabellicornis, on a different date, but in exactly the same area – the checkpoint at Doi Chiang Dao – as I had observed large number of Great and Common Windmills (Atrophaneura dasarada and A. polyeuctes) (below).
- Halpin, C. G., Skelhorn, J., & Rowe, C. (2013). Predators’ decisions to eat defended prey depend on the size of undefended prey. Animal behaviour, 85(6), 1315-1321.
- Komata, S., Lin, C. P., Iijima, T., Fujiwara, H., & Sota, T. (2016). Identification of doublesex alleles associated with the female-limited Batesian mimicry polymorphism in Papilio memnon. Scientific reports, 6, 34782. https://www.nature.com/articles/srep34782
- Nishida, R. (1994). Sequestration of plant secondary compounds by butterflies and moths. Chemoecology, 5(3-4), 127-138.
- Nishida, R. (2017). Chemical Ecology of Poisonous Butterflies: Model or Mimic? A Paradox of Sexual Dimorphisms in Müllerian Mimicry. In Diversity and Evolution of Butterfly Wing Patterns (pp. 205-219). Springer, Singapore. https://link.springer.com/chapter/10.1007/978-981-10-4956-9_11
- Prudic, K. L., & Oliver, J. C. (2008). Once a Batesian mimic, not always a Batesian mimic: mimic reverts back to ancestral phenotype when the model is absent. Proceedings of the Royal Society of London B: Biological Sciences, 275(1639), 1125-1132.
- Quicke, D. L. (2017). Mimicry, Crypsis, Masquerade and Other Adaptive Resemblances. John Wiley & Sons.