The Plain Tiger, Danaus chrysippus (Linnaeus, 1758), is a butterfly with an enormous distribution – from West Africa to New Zealand (1, 2). There are a large number of different forms or subspecies comprising what is called a ‘species complex’. This is a name given to a group of insects by taxonomists when they don’t really know, or disagree, as to whether the different forms are genuine species, or subspecies, or semi-species, or just a confusing plethora of hybridizing populations evolving before our eyes!

Evidence of the variation in this ‘species complex’ is reflected in the variety of common names for this butterfly: Plain Tiger, Common Tiger, African Monarch, Lesser Wanderer, African Queen and so on. There is an even longer list of synonyms, that is to say, alternative scientific names that have been used, superseded or revised down the centuries.

To get round the problem of trying to come up with a name for an entity which includes a number of different forms or subspecies, biologists use the term sensu lato, meaning ‘in the broad sense’. Hence Danaus chrysippus sensu lato (s.l.) is the term used to describe all of the different forms, subspecies, or what have you, of this polytypic butterfly, which occur throughout most of the Afrotropical, Oriental and Australian Regions. There are of course definitive biological features which distinguish the butterflies within this D. chrysippus complex, i.e. from all other Danaus species. These include the presence of certain white scales and black spots on the hind-wings (1).

The Oriental form of the Plain Tiger, Danaus chrysippus chrysippus Linnaeus, 1758 – has perhaps the widest distribution, from Morocco all the way across the Old World to southern Japan. The life history of this butterfly has been comprehensively described and illustrated on the excellent, Butterflies of Singapore, website (3). There are also a large number of photographs of this subspecies on the Butterflies of India website (4).

The subspecies shown here, Danaus chrysippus bataviana, has a much more limited distribution and occurs only on Java, Sulawesi (part) and the Lesser Sunda Islands, which include Bali, all in Indonesia. These photographs were taken on Bali. The upper hind wings of this subspecies appear to be darker (described as brown by one authority) than those of D. c. chrysippus (5). There are also reports of this subspecies occurring in Malaysia, together with D. c. chrysippus, in isolated but sometimes dense colonies (6), which makes me wonder just how geographically distinct these different subspecies are. Indeed, Smith (2014) states that: ‘D. c. bataviana and D. c. chrysippus are distinct subspecies separated by a narrow, dynamic hybrid zone which has, and may still be, on the move’. It would be interesting to know whether anyone has studied this butterfly across these regions?

It is fairly easy to tell the sexes apart in these species. The males have a large black spot on the hind-wings which the females lack. On the dorsal or upper-side of the hind-wing, this feature bulges outwards (see photo below, of Plain tiger butterfly in profile) and is called an alar pocket (7).

On the ventral, or underside, of the hind-wing, the so-called, subtornal brand is also visible as a black spot, but unlike on the top (dorsal) side, it has a prominent white spot within it. This lies alongside the third wing vein from the left (or central) side of the hind-wing, looking down. This white spot is the surest way to identify a male. The female has no such black mark with a white centre (see directly below).

Male milkweed butterflies (subfamily, Danainae, in the family Nymphalidae) have a pair of specialised scent-producing organs, called hair-pencils, at the tip of their abdomens. During courtship the hair pencils are everted to form two round bundles of hairs that look rather like toilet brushes! (See image on website below, #9). The function of these organs is to brush the females antennae and transfer a fine dust of pheromone particles. If the female is responsive to this advance, she flies down to the ground, where the male joins her.

It is known that the hair pencils of the male are first inserted into their alar pockets in order to make contact with the glands in this organ which produce a pheromone. Presumably they do this before everting the bristles? Males are unable to excite the females into copulation without first extracting the substance emanating from these alar glands. Armed with the dust-like pheromone particles he is able to dance in front of the female and transfer the magic potion!

There is however, no guarantee that the female will be receptive. Females might reject males for a number of reasons; he just might not look right (being a different subspecies perhaps); he might be too small (she may be seeking a large spermatophore produced by a large male); he might not smell right (the sex pheromones and volatile cuticular hydrocarbons); or she may have already mated (1). Bad luck! She indicates her refusal by bending her abdomen in a certain way and flapping her wings. It would be nice to be able to photograph these behaviours.

But if the courtship sequence is successful, the pair will remain locked together in copula for a good number of hours. Smith (2014) recorded an average time of 3.5 hours in copula for captive D. chrysippus (5), with some couples remaining together for up to 5 hours. The pair fly off together in what is called a post-nuptial flight. According to Smith (2014), the male is usually larger than the female – although other websites, including Wikipedia, state that the male plain tiger is smaller than the female – and he easily carries her off to a site where they can remain undisturbed for the remainder of the time they are locked together. The male aedeagus (penis) fits into a pocket beneath the ovipositor of the female and the sex organs are locked tightly together whilst the spermatophore is transferred. The female remains passive with limbs folded (see photo below). Smith (2014) reports a sighting of large female carrying a smaller male, so as is often the case in biology, there are no hard and fast rules about who is on top! It is possible that there is variation between subspecies with regard to size and role in terms of who is carrying whom?!

Much of this blog was based on information contained in the excellent volume on African Queens by David Smith, FRES, FLS. The main focus of the book is Danaus chrysippus (L.) sensu strico, which he considers is a ‘superspecies’ – a ‘complex of actively evolving populations’ comprising ‘incipient (imperfectly formed but actively evolving) semi- and subspecies’, rather than a single polymorphic species. Recent research has however, suggested that the D. chrysippus species complex should be separated into two separate species: a polytypic – meaning containing more that two subspecies – D. chrysippus, and monotypic D. petilia.  So not a very big change, as most of the subspecies remain. These two new species occur in distinct but contiguous areas, separated by Lydekker’s Line, separating Australian and Oriental faunas (see map in reference 1). Danaus petilia, known as the Lesser Wanderer, is a migratory species, found in Australia (8).

Whether there are one, two or three species, or seven or eight subspecies – or semi-species – need not concern us! Such matters are best left to taxonomists to sort out! As far as I am concerned it is a beautiful butterfly and I look forward to seeing and photographing some more of the different forms of this butterfly, which represents evolution in action.

Whilst writing this blog, I came across a similar account of mating in Plain tigers by another blogger: Krishna Mohan (10).

All of these images, apart from the one of the female from Komodo NP, were taken in Bali Barat NP, Bali, Indonesia, in October 2016.

1. Braby, M. F., Farias Quipildor, G. E., Vane-Wright, R. I., & Lohman, D. J. (2015). Morphological and molecular evidence supports recognition of Danaus petilia (Stoll, 1790)(Lepidoptera: Nymphalidae) as a species distinct from D. chrysippus (Linnaeus, 1758). Systematics and Biodiversity, 13(4), 386-402.
2. Lushai, G., Zalucki, M. P., Smith, D. A., Goulson, D., & Daniels, G. (2005). The lesser wanderer butterfly, Danaus petilia (Stoll 1790) stat. rev.(Lepidoptera: Danainae), reinstated as a species. Australian Journal of Entomology, 44(1), 6-14.
3. http://butterflycircle.blogspot.co.uk/2010/11/life-history-of-plain-tiger.html
4. Lovalekar, R., K. Saji, T. Bhagwat & Manoj P. 2017. Danaus chrysippus Linnaeus, 1758 – Plain Tiger. Kunte, K., P. Roy, S. Kalesh and U. Kodandaramaiah (eds.). Butterflies of India, v. 2.24. Indian Foundation for Butterflies.
   http://www.ifoundbutterflies.org/sp/744/Danaus-chrysippus
5. Smith, D. A. (2014). African queens and their kin: a Darwinian odyssey. Taunton, UK: Brambleby Books.
6. Smith, D. A., Gordon, I. J., & Allen, J. A. (2010). Reinforcement in hybrids among once isolated semispecies of Danaus chrysippus (L.) and evidence for sex chromosome evolution. Ecological Entomology, 35(s1), 77-89.
7. Urquhart, F. A. 1976. Alar pocket of the male Monarch butterfly (Danaus p. plexippus) (Danaidae: Lepidoptera). Canadian Entomologist 108:777-782.
8. http://www.brisbaneinsects.com/brisbane_nymphs/LesserWanderer.htm
9. http://www.flickriver.com/photos/lionyang/2228664296/
10. http://drkrishi.com/mating-trouble/