Danaus chrysippus (Linnaeus, 1758)
📷:Jeevan Jose (CC)
1 General Information
Danaus chrysippus, also known as the plain tiger, is a medium-sized (roughly the size of an Oreo cookie) butterfly which can be found in many gardens and parks in Singapore. It has orange wings with black borders dotted by white spots. This orange-black-white colour scheme is recognisable from afar, and is probably what gave it the 'tiger' part of its name. A few other 'tigers' can also be found in Singapore, but it is fairly easy to distinguish the plain tiger from its lookalikes.
The plain tiger is not rare nor endangered, and its name can sound boring and 'plain' (hur hur). However, it has interesting relationships with certain toxic plants, and is involved with interactions with other animals, which makes this species worth looking at (it's easy on the eyes as well!).
Distribution & Habitat
Only one of the 3 known subspecies of the plain tiger, Danaus chrysippus chrysippus, can be found in Singapore. This subspecies exists in two forms here — the more common form has white upper hindwings while the other has orange ones.
Danaus chrysippus chrysippus form alcippoides with white hindwings. 📷: Chan Jie Yi
Danaus chrysippus chrysippus form chrysippus with orange hindwings. 📷: Viren Vaz (CC)
The plain tiger is almost always found in open areas, like gardens and parks, close to their host plants. They can easily be found at HortPark, Coney Island and even the Istana Park, right in the middle of a bustling shopping district. Other sightings, recorded by the Global Biodiversity Information Facility (GBIF), are shown in the map below.
Map of GBIF sightings in Singapore made with the use of OpenStreetMap.
The plain tiger can be found over a wide geographic range. It has been sighted across the whole of Africa, Mediterranean Europe, the Middle East, much of Asia, and even Australia.
Map of global GBIF sightings made with the use of OpenStreetMap.
2 Relationships with toxic plants and other animals
Host plant specificity
In Singapore, mature female plain tigers lay their eggs almost exclusively on only 2 plant species — Asclepias curassavica, also known as bloodflower, and Calotropis gigantea, also known as giant milkweed. These plants belong to a group collectively known as milkweeds. Milkweeds secrete latex which contains chemicals called cardenolides, which are ingested by the larvae as they feed on the plant. The cardenolides are toxic to potential predators (but not the larvae!), and can be stored till maturity.
Cardenolides had evolved in plants as a defense against herbivores, but some herbivores, including plain tiger larvae, evolved enzymes to become able to process these cardenolides. Since herbivory is costly to plant growth, the milkweeds have evolved stronger and stronger cardenolides, but the larvae have also adapted to the chemicals. This is an example of an evolutionary arms race, and can lead to tight associations between species.
Strangely, while the plain tiger has been classified as 'native' to Singapore, its host plants have been classified as 'exotic'. This may lead one to wonder how the plain tiger survived in Singapore before the two host plant species were introduced here.
Native vs. Exotic species
Native species are species which are present in a locality "without human intervention", while exotic species are those "whose presence is a result of either intentional or unintentional human involvement". Accurate classification of a species as either native or exotic requires historical knowledge of its geographical distribution. The plain tiger's host plants do not occur naturally in Singapore, and are cultivated mainly for ornamentation.  This lends support to the classification of the host plants as exotic species.
The earliest records of the plain tiger in Singapore date back to the early 1900s, around the same time its host plants were recorded. As such, it is not clear if the plain tiger was present in Singapore before the introduction of the host plants. One possibility is that the range of the plain tiger expanded to include Singapore after its host plants were introduced.
Defence against predators
Other than the cardenolides obtained during the larval stage, adult plain tigers also ingest and store another type of toxic substance called pyrrolizidine alkaloids (PAs). These chemicals cause plain tigers to be inedible (usually causing vomiting) to many predators, especially birds. Predators which have suffered the negative effects of eating a plain tiger subsequently learn to avoid eating the same type of butterfly because of its bright, noticeable coloration and pattern. This 'strategy' of using warning colours to ward off predators is also known as aposematism.
📷: Jeevan Jose (CC)A bloodflower plant.
A giant milkweed plant at Istana Park. 📷: Chan Jie Yi
Female Danaid eggfly (compare with the pictures of plain tigers on this site!). 📷: Ajith U (CC)
Looking like the plain tiger offers a similar level of protection as being a plain tiger, given that predators use visual cues to learn to avoid toxic butterflies. Some species of butterflies which are actually edible to predators have evolved to look extremely similar to (i.e. mimic) the plain tiger or other toxic species — one example is Hypolimnias missippus (also known as the Danaid eggfly) which can be found in Africa. This is known as Batesian mimicry.However, there are no known living, locally extinct or globally extinct Batesian mimics of the plain tiger in Singapore, which could be due to the fact that the plain tiger may not actually be a native species.
In Müllerian mimicry, two or inedible species evolve to resemble each other. This benefits all the species involved, because each species will on average be attacked fewer times because predators learn to avoid the shared coloration/pattern. In Uganda, the plain tiger forms a Müllerian mimicry ring with Acraea encedon and Acraea encedana.There are no known instances of Müllerian mimicry involving the plain tiger in Singapore. However, Müllerian mimicry rings could have formed where multiple inedible 'tiger' species are found together (e.g. Coney Island). More research is required to know whether the 'tiger' species are Müllerian mimics of each other.
Plain tigers vs. other 'tigers'
Other than the plain tiger, Singapore is also home to two other similar-looking species of 'tigers' — Danaus genutia, known as the common tiger, and Danaus melanippus, known as the black veined tiger. The plain tiger can easily be distinguished because it does not have thick black stripes on its wings, unlike the other species.
Very recently, in 2020, a fourth 'tiger' species that had never before been seen in Singapore was spotted at Pulau Ubin. This species is Danaus affinis, also known as the swamp tiger. The swamp tiger is considerably smaller than the other 'tigers' featured above, and seems to have flown over from Malaysia.
📷: Sharp Photography (CC)Swamp tiger, which also has black stripes on its wings.
Males vs. females
Male and female plain tigers look extremely similar, but males can easily be differentiated from females with the presence of an additional black-and-white spot on its hindwing. This spot is in fact a pheromone pouch, and is important for courtship and mating.
4 Life cycle
The plain tiger follows the general four-stage life cycle familiar to many people. Studies determining the lifespan of plain tigers in the wild are scarce — current knowledge suggests the average lifespan could be anywhere from 8 to 18 days.
The four main life cycle stages (clockwise from top): egg, larva, pupa, adult. 📷:
The eggs of the plain tiger are laid singly on the underside of host plant leaves, instead of multiple eggs being laid in a clutch like in other butterfly species. Plain tiger eggs are small, measuring only 0.5 mm across. The eggs hatch into larvae in about 3 to 5 days.
The larvae (or caterpillars) of the plain tiger go through five instar stages, which are periods of development in between moulting events. The larva grows bigger with each successive moult. As with other members of the Danaus genus, the older larvae of the plain tiger are mainly white/grey with characteristic yellow-and-black stripes horizontally across the body.
The pupal stage of the plain tiger lasts about 9 to 15 days, where the caterpillar hardens to become a green, sometimes brown, chrysalis (not a cocoon!). If you've ever wondered what happens in a chrysalis, the video below could be a good place to start.
Adult male and female plain tigers do not differ significantly in size, and span roughly 7 cm from wingtip to wingtip.
Adult male plain tigers have a pouch on their hindwing where they store pheromones used to attract mates. The males also have structures called hair-pencils at the ends of their bodies, which are dipped into the pheromone pouches then fanned towards females to attract them. During mating, the male and female are at rest facing away from each other, with the male clasping onto the female.
5 Taxonomy & Systematics
Danaus chrysippus was described by Carl Linnaeus in 1758, making it one of the first species ever to have been scientifically described. The description in Latin roughly translates as: "wings entirely orange, black margins with white dots, back with black dots".
Scan of original description in Systema Naturæ made available by the Biodiversity Heritage Library (CC).
Scientific & Common names
Danaus chrysippus (Linnaeus, 1758) was originally described by Carl Linnaeus under the genus Papilio Linnaeus 1758. Papilio was later broken up into smaller genera, and chrysippus was placed under the genus Anosia Hübner 1816. Eventually, Anosia was merged with Danaus Kluk 1802 when it was discovered that Anosia was a paraphyletic group.
Danaus chrysippus is known colloquially as the plain tiger, African Queen or African Monarch. The name 'tiger' refers to its tiger-like colour scheme, while 'Queen' and 'Monarch' are common names of the similar-looking Danaus gilippus and Danaus plexippus respectively. The queen and monarch butterflies are found mainly in the Americas, as opposed to the plain tiger which is found throughout Africa (and Eurasia), which explains the 'African' part of its alternative monikers.
Danaus was a king of Libya in Greek mythology. Chrysippus was one of Danaus' nephews and also the husband of Chrysippe, one of Danaus’ 50 daughters. According to Greek myth, Chrysippe, along with her 49 sisters, were ordered by their father to kill their husbands. Many other members of the original genus Papilio were also named by Linnaeus after the murdered bridegrooms.
Danaus' daughters murdering their husbands. Illustration by Robinet Testard (CC).
A lectotype has been chosen from the specimens that Linnaeus worked with when describing the species. This lectotype is stored at the Linnaean Society of London (LSL), and is available for viewing here.
Lectotype stored at LSL. Despite being nearly 300 years old, this specimen is extremely well-preserved!
Genus: Danaus Kluk 1802
Species: Danaus chrysippus (Linnaeus, 1758)
There are three recognised subspecies: Danaus chrysippus chrysippus, Danaus chrysippus alcippus (Cramer, 1777) and Danaus chrysippus orientis (Aurivillius, 1909).
Species, subspecies and forms
The word "species" is almost certainly one that everyone has heard of, but what exactly is a species? The short (and disappointing) answer is there is no agreement on what a species is. Different scientists have different definitions for what a species is — these are known as species concepts. There are over 20 species concepts, but none of them can 1) apply to every lifeform and 2) provide clear enough boundaries between species, at the same time. In essence, there is no 'right' species concept as of yet.
However, the species concept most commonly applied to sexually reproducing animals, like the plain tiger, is the Biological Species Concept (BSC). Very simply and intuitively, the BSC states that two groups of organisms are considered different species if they cannot interbreed naturally.
Subspecies, then, are groups of organisms that can interbreed naturally, but usually differ in terms of their geographic range, physical appearance, and/or behaviour such as migration timings. Subspecies can be named formally, and in recent years, there usually are genetic bases for the designation of subspecies. On the other hand, forms are strictly informal terms, and are used rather loosely to refer to members of the same species that look different. More in-depth explanations and examples are available here and here.
Phylogeny (or phylogenetics) is, put simply, the study of evolutionary relationships between organisms. A fairly recent phylogenetic study on the genus Danaus was carried out in 2005 and used nuclear and mitochondrial DNA, as well as physical characteristics, to infer the relationships between 11 Danaus species.The results of this study suggests that the closest evolutionary relative of D. chrysippus is D. dorippus, once thought to be a subspecies of D. chrysippus.
A more recent study has however cast doubt on how well-resolved the phylogeny of the genus Danaus is. In 2016, a phylogenetic study that used a different gene (ATPα) from the 2005 study produced a phylogeny that conflicted older studies. The 2016 study suggests that the closest evolutionary relative of D. eresimus is D. plexippus/erippus, while the 2005 study suggests that the closest evolutionary relative is instead D. gilippus. According to the newer study, one possible reason for this inconsistency is that the ATPα underwent introgression. More of such inconsistencies could be present in the genus Danaus, so more research is required for us to be certain of the evolutionary relationships between Danaus species.
 Bootstrap support values are shown in red. Branch lengths are shown in black.Phylogenetic tree for 5 Danaus species.
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This page was authored by Sim Hong Jhun (firstname.lastname@example.org)
Last curated on 11 Jan 2021