The Ceylon tree nymph (''Idea iasonia'') is a species of

nymphalid The Nymphalidae are the largest family of butterflies, with more than 6,000 species distributed throughout most of the world. Belonging to the superfamily Papilionoidea, they are usually medium-sized to large butterflies. Most species have a red ...

butterfly Butterflies are insects in the macrolepidopteran clade Rhopalocera from the order Lepidoptera, which also includes moths. Adult butterflies have large, often brightly coloured wings, and conspicuous, fluttering flight. The group comprise ...

in the subfamily

Danainae Danainae is a subfamily of the family Nymphalidae, the brush-footed butterflies. It includes the Daniadae, or milkweed butterflies, who lay their eggs on various milkweeds on which their larvae (caterpillars) feed, as well as the clearwing butt ...

. It is

endemic Endemism is the state of a species being found in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also found else ...

to Sri Lanka. First described by John Westwood in 1848, the Ceylon tree nymph can be found in both wet and dry zones of Sri Lanka. It is the largest member of the family Danaidae in that country. It is listed as a near threatened species in the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is the world's most comprehensive inventory of the global conservation status of biol ...

Taxonomy

The species was first described by English entomologist John O. Westwood in 1848, as ''Hestia iasonia''. For several years it was considered to be only an island race of '' I. lynceus'', a species found in eastern Asia. However the two species have differences in their wing shapes and in the male genitalia. It is of the genus ''Idea'', and belongs to the subfamily

of the family

Nymphalidae The Nymphalidae are the largest family of butterflies, with more than 6,000 species distributed throughout most of the world. Belonging to the superfamily Papilionoidea, they are usually medium-sized to large butterflies. Most species have a red ...

. Its binomial name is ''Idea iasonia''.

Description

The Ceylon tree nymph has a wingspan of 110–155 mm, making it the largest member of the family Danaidae in Sri Lanka. Both its wings have similar patterns and colouration. The wings are of a translucent silvery-white colour. The forewings are almost twice as long as their width. The female is larger than the male, and the males have narrower forewings than the females. The surface area of the Ceylon tree nymph's wings is relatively large when compared with its weight; this allows it to fly with little effort and stay aloft for long periods of time. Ceylon tree nymphs from the dry zone of the country are usually larger in size and lighter in colour than ones from the wet zone.

Distribution and habitat

The species is

to Sri Lanka. There are two populations of the Ceylon tree nymph. The smaller and darker variety is found in the wet zone of Sri Lanka from sea level to about . They usually inhabit the sub-canopies of lowland tropical rain forests. The other variety, which is larger and lighter coloured, is found in the low country dry zone. They are usually encountered near water courses.

Behaviour

Since the Ceylon tree nymph requires very little effort to fly, its wing beats are very slow, so slow that the individual movements of each wing can be easily observed. Most of its time is spent flying and hovering in the high tree canopies. However, it descends to ground level to feed and to breed, but does not rest on the ground. It usually rests on the ends of dead branches or twigs.

Mating In biology, mating is the pairing of either opposite- sex or hermaphroditic organisms for the purposes of sexual reproduction. ''Fertilization'' is the fusion of two gametes. ''Copulation'' is the union of the sex organs of two sexually reprod ...

occurs at ground level and the male and female fly together for an hour or more before mating. The male releases

pheromones A pheromone () is a secreted or excreted chemical factor that triggers a social response in members of the same species. Pheromones are chemicals capable of acting like hormones outside the body of the secreting individual, to affect the behavio ...

and other chemicals from its

hair-pencil Hair-pencils and coremata are pheromone signaling structures present in lepidopteran males. Males use hair-pencils in courtship behaviors with females. The pheromones they excrete serve as both aphrodisiacs and tranquilizers to females as well as r ...

s to stimulate the female. These include danaidone, a poisonous substance that helps to protect it from predators, which is later passed on to the eggs. The early stages of life of the Ceylon tree nymph are not well recorded. One account by naturalists

Lionel de Nicéville Charles Lionel Augustus de Nicéville (1852 in Bristol – 3 December 1901 in Calcutta from malaria) was a curator at the Indian Museum in Calcutta (now Kolkata). He studied the butterflies of the Indian Subcontinent and wrote a three volume mono ...

and N. Manders dating from about 1900 describes the larva as "velvety black with four pairs of long filamentous tentacles" with each segment of its body marked with a pale yellow band. The record further mentions that it has twelve segments and that the sixth segment has a "large oval crimson spot". Its head and legs are black.

Threat

In the IUCN Red List, the Ceylon tree nymph is listed as lower risk/near threatened. The main threat faced by the Ceylon tree nymph is the destruction of its habitat. However, various direct steps have been taken for the conservation of this species. Several of its naturally occurring areas are protected areas, such as the forest reserve of Sinharaja.

References

External links

*
''Idea iasonia''
Sri Lanka Wild Life Information Database {{Taxonbar, from=Q914978 Idea (butterfly) Butterflies of Sri Lanka Taxonomy articles created by Polbot Butterflies described in 1848