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Tigers in the grass: milkweeds and mimicry

Common tiger (Danaus genutia) male. Doi Chiang Dao, Thailand

One of the pleasures of trying to photograph butterflies, is that you never know what you might find. One afternoon last November (2017) in northern Thailand, as the sun was setting over the nearby mountain (Doi Chiang Dao), I came across two beautiful butterflies – fairly common species – stocking up on nectar before the sun went down. The light was fairly low and good for back-lit photographs of the butterflies as they fed on daisy-like flowers in an abandoned weed field. By sitting low down among the weeds, I was able to get some shots that I was pleased with. What constitutes a good shot is a matter of taste, but I like natural lighting, although it is not always possible in dimly lit forests.

Sun setting behind the mountain (Doi Chiang Dao), northern Thailand

The two common species were the Common tiger (Danaus genutia) and the Broad Blue Tiger (Tirumala limniace), sometimes just called the Blue tiger. Both are danaid or milkweed butterflies, members of Subfamily Danainae. These butterflies are poisonous and hard to kill. Once predators lean how distasteful they are, they leave them alone.

Broad Blue Tiger (Tirumala limniace). Doi Chiang Dao, Thailand.

Both butterflies sequester toxins from their host plants – the larvae mostly feed on plants in the milkweed Family, Asclepiadaceae  – many of which contain cardiac glycosides  – which the butterflies use to make themselves poisonous and distasteful to predators. If birds make the mistake of trying to eat them, they soon release them and learn to avoid them in future. With such a good system for avoiding being eaten, it is not surprising that other, non-toxic butterfly species have evolved to look like them: Batesian mimicry.

Common tiger (Danaus genutia) male. Doi Chiang Dao, Thailand

There are various theories as to why mimicry is sex-limited (to females) in so many butterfly species. One theory is that females are more at risk from predation than males; perhaps as a result of carrying heavy loads of eggs, or maybe because they engage in lengthy oviposition behaviour. Another theory, is that because females do the choosing when it comes to mating – and they tend to like males who look flashy, i.e. bright and iridescent (this is a good indication of male fitness) – males end up being non-mimetic. Finally, a third theory holds that brightly coloured, rather than mimetic males, do better in territorial contests and are therefore selected by default in this way. (see Refs 1 and 2). A further complication arises as a result of the fact that the females often come in different forms, or dimorphs. For example, see here.

Broad Blue Tiger (Tirumala limniace). Doi Chiang Dao, Thailand.

The Common Wanderer (Pareronia anais) – a member of a totally different family, the Pieridae – is said to be a mimic of the Blue Tiger (Tirumala limniace), but as is often the case, only the females do the mimicking! The female P. anais (below) looks like a reasonable mimic of the Broad Blue Tiger (T. limniace), but it is by no means perfect; but probably good enough to fool a predator like a bird, which might have encountered one before. In any case, predators tend to be cautious; perhaps they give it the benefit of the doubt when it come to a distasteful mouthful!

The Common Wanderer, Pareronia anais (female). “Pareronia hippia-Silent Valley-2016-08-15-001” © 2016 Jee & Rani Nature Photography is used here under a CC BY-SA 4.0 License

The male Common Wanderer (Pareronia anais) looks quite different (below). He is not going to fool anyone, or is he? Perhaps he trying to make the best of two conflicting demands: looking nice and bright and flashy to attract the ladies, but also trying to look a bit like a distasteful danaid. Hoping that some bird might give him the benefit of the doubt as he sits warming up in the sun?

Common Wanderer (Pareronia anais) male. Doi Chiang Dao.

The Leopard lacewing (Cethosia cyane) and females of the Common Palmfly (Elymnias hypermnestra) are said to be Batesian mimics of the Common tiger butterfly (Ref 3). In this case it is the male Leopard lacewing which looks most like the Common tiger to me (below).

Leopard Lacewing – Cethosia cyane, male . This file is licensed under the Creative Commons Attribution-Share Alike 2.0 Generic license. Pavel Kirillov.

The female is a rather pale version and without the red/orange colour is not going to fool any would be predators, I think! I managed to grab this shot of one (below).

Leopard lacewing (Cethosia cyane) female. Thailand

The upper (dorsal) wing surfaces of the Common palmfly (E. hypermnestra) are a much better likeness to the Common Tiger (D. genutia), to my mind. Unfortunately, I don’t have a photograph of one and there are none in the public domain on Wiki Commons! These butterflies invariably come to rest with their wings folded and – in the case of the females – their beautiful mimicry patterns hidden (below); but there is one shown on this excellent Indian website, Butterflies of India, here.

Common palmfly (Elymnias hypermnestra agina), undersides. The mimicry patterns are hidden in this case!

For any American (North and South) readers, the common tiger, Danaus genutia, is fairly similar in appearance to the Monarch butterfly (Danaus plexippus) (below).

Monarch Butterfly (Danaus_plexippus)
© Derek Ramsey / derekramsey.com / Used with permission

In a previous blog I described the courtship and mating of a related species: the Plain Tiger, Danaus chrysippus. Plain and Common Tigers look quite similar and are said to be Müllerian mimics, which implies that the bad experience a predator has when trying to eat either of them, will also extend to the other. Mutual protection as it were. The males of both of these species have a large black, oval-shaped spot – the so-called alar pocket or scent brand – on the (dorsal) upper-side of the hind-wing, which bulges outwards from the wing surface (below). This is where the male makes and keeps his pheromones! I was very fortunate to capture this image, even if it is a bit blurry (!), which shows the sex brand sticking up above the surface of the left hind-wing.

Common tiger (Danaus genutia) male, in flight. Sex brand is shown (in circle).

Male Blue Tigers are said to have a pouch containing scent scales, but I cannot see any sign of it in these photos, so I am not sure if the Blue Tigers are male or female.

As always, I start with photographs, enjoying the fun of trying to capture a good image; chasing butterflies in the sun; the virtual equivalent of a hunter and his prey! In this case nothing is harmed other than pixels! I often notice things in the photographs at a later date, when I come to examine and process them on the computer. This leads to a session of research and ‘Googling’ and, if I am lucky a story emerges.

References

  1. Joron, M., & Mallet, J. L. (1998). Diversity in mimicry: paradox or paradigm?. Trends in Ecology & Evolution13(11), 461-466.
  2. Kemp, D. J. (2007). Female butterflies prefer males bearing bright iridescent ornamentation. Proceedings of the Royal Society of London B: Biological Sciences274(1613), 1043-1047.
  3. Kunte, K. (2000). India, a Lifescape: Butterflies of Peninsular India. Universities Press.

Links

  1. http://butterflycircle.blogspot.co.uk/2010/02/butterfly-of-month-february-2010.html
  2. https://en.wikipedia.org/wiki/Tirumala_limniace
  3. http://www.butterflycircle.com/wordpress/?p=628
  4. https://en.wikipedia.org/wiki/Pareronia_hippia

rcannon992 View All

I am a retired entomologist with a background in quarantine pests and invasive invertebrates. I studied zoology at Imperial College (University of London) and did a PhD on the population dynamics of a cereal aphid (Metopolophium dirhodum) in the UK. I spent 5 years with the British Antarctic Survey studing cold hardiness of Antarctic invertebates and 17 years with the Food and Environment Research Agency. My main interests now are natural history, photography, painting and bird watching.

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