The Plain Tiger (Danaus chrysippus) or - outside Asia - African Monarch is a common butterfly which is widespread in Asia and Africa. It belongs to the danaine ("Crows and Tigers") subfamily of the brushfooted butterfly family Nymphalidae.
The Plain Tiger can be considered the archetypical danaine of India. Accordingly, this species has been studied with in greater detail than other members of its subfamily occurring in India.
The Plain Tiger is a medium sized butterfly with a wingspan of about 7–8 cm. The body is black with many white spots. The wings are tawny the upper side being brighter and richer than the underside. The apical half of the fore wing is black with a white band. The hind wing has 3 black spots around the center. The hind wing has a thin border of black enclosing a series of semicircular white spots.
Background color and extent of white on the forewings varies somewhat across the wide range; see Systematics and taxonomy below.
The male Plain Tiger is smaller than the female, but more brightly colored. In addition, male danaines have a number of secondary sexual characteristics. In the case of the Plain Tiger, these are:
On the other hand, the former subspecies petilia is nowadays recognized as a good species, the Lesser Wanderer. More enigmatic is the status of the former subspecies (or forms) dorippus and bataviana. These are tentatively also regarded as a distinct species, the "Dorippus Tiger" (Danaus dorippus).
However, it appears (from analysis of mtDNA sequences, which are only inherited from the mother) that the Dorippus Tiger is the product of an ancient lineage of Danaus hybridizing with Plain Tiger females. As the Plain Tiger is known to be parasitized at least occasionally by Spiroplasma bacteria which selectively kill off male hosts, a subsequent scarcity of Plain Tiger males might have led to this hybridization and the evolution of the Dorippus Tiger. From the color pattern of this species, it can be assumed that the ancient lineage had no black apex on the forewings, as this character is still absent in D. dorippus.
The presumed subspecies cratippus most likely belongs to either the Lesser Wanderer or the Dorippus Tiger, but confirmation of its taxonomic status requires more research. In any case, these three species are closely related; their closest relatives, in turn, might be the Soldier (D. eresimus) and Queen (D. gilippus) butterflies.
Several local forms have been described from Asia:
On the other hand, the plethora of named taxa from Africa are apparently F1 or F2 hybrids between the Plain Tiger subspecies (the contact zone of which is in the general area of Uganda) and/or D. dorippus:
This butterfly is perhaps the commonest of Indian butterflies and is a familiar sight to practically everyone on the subcontinent. It flies from dawn to dusk, frequenting gardens, sipping from flowers and, late in the day, fluttering low over bushes to find a resting place for the night.
As usual for diurnal butterflies, this species rests with its wings closed. When basking it sits close to the ground and spreads its wings with its back to the sun so that the wings are fully exposed to the sun's rays.
The butterfly also has a tough, leathery skin to survive such occasional attacks. When attacked it fakes death and oozes nauseating liquid which makes it smell and taste terrible. This encourages the predator to release the butterfly quickly. The Plain Tiger thus has the ability to recover "miraculously" from predator attacks that would kill most other butterflies.
The protection mechanisms of the Plain Tiger, as of the other danaines, and indeed of all colorful unpalatable butterflies, result in predators learning this memorable aspect at first hand. Predators soon associate the patterns and habits of such butterfly species with unpalatability to avoid hunting them in future.
This advantage of protection has led to a number of edible butterfly species, referred to as "mimics", evolving to resemble inedible butterflies, which are referred to as the "model". The resemblance is not only in color, shapes, and markings, but also in behavioural and flight patterns. This form of mimicry - where an edible species mimics an inedible species - is known as Batesian mimicry.
The mimics can resemble the models very closely. In some cases, it requires examination in hand and reference to field guides to tell them apart. The Plain Tiger is specifically mimicked by the following butterflies:
The following butterflies have a general resemblance common to both the Plain Tiger and the Common Tiger:
The similarity between the Plain and Common Tigers makes them Müllerian mimics, as the adverse experience a predator makes with either species will also protect the other.
The female Plain Tiger perches on the upperside of a leaf and, curling its abdomen around the edge, lays an egg on the underside. Only one egg is laid per leaf to avoid overcrowding of the caterpillars. The egg is silvery white, shiny, tall, bullet-shaped with an apical point and ribbed sides.
After the caterpillar hatches, its first meal is the eggshell itself. It lives its entire larval life on the lower side of the leaves. During the first few days it has a very interesting manner of feeding: It will take up a spot on the underside of the leaf and nip a complete circle around itself in the lower cuticle of the leaf. By doing this it stops the poisonous sap of its host plant from flowing into the area inside the circle. It then proceeds to eats the lower surface of this area, leaving the upper cuticle intact.
As it grows, it eats both the lower and upper cuticle of the circle thus leaving smallish circular holes in the leaves of its host plant. When its mandibles are large enough it eats the complete leaf by gnawing at the edges.
The caterpillar is uniformly cylindrical. Its body is covered with bands of black and white interspersed with thick, yellow, dorsolateral spots. The most striking characteristics are the 3 pairs of long and black tentacle-like appendages. The first pair is moveable and also the longest. The tentacles are present on the 3rd, 6th and 12th segments. The head is shiny, smooth and has alternating black and white semicircular bands. The legs and prolegs are black and the prolegs have white bands at their bases.
The pupa hangs freely from the support. It is widest at the 7th abdominal segment where it has a double chain of extremely tiny golden and black beads. There are tiny golden spots on the shoulders and wing-cases. The rest of the pupa is pale green with a smooth surface. The pupa is light pink when formed among dry or unnatural objects.
Host plants from other families include Dyerophytum indicum (Plumbaginaceae), Ficus (Moraceae; recorded on F. laevis, F. racemosa), Ipomoea (Convolvulaceae; recorded on I. alba, I. bona-nox), Lepisanthes rubiginosa (Sapindaceae) as well as some Euphorbiaceae, Malvaceae, Poaceae, Rosaceae and Scrophulariaceae.