Ceylon tree nymph  (Idea iasonia)

The Ceylon tree nymph is classified as Near Threatened (NT) by the IUCN Red List (1).

The Ceylon tree nymph (Idea iasonia) is a beautiful silvery white butterfly (2) and is the largest member of the Danaidae family in Sri Lanka (3). Both wings are a translucent silvery white, and the forewings are almost twice as long as they are wide (3). The sexes are similar, although females tend to be larger in size (2) and males have narrower wings (3). Individuals from the dry zone tend to be larger and lighter in colour than those from the wet zone, and some individuals may have a reddish hue over the wing surface (3). The fact that the surface area of the wings is very large relative to the weight of this butterfly allows it to fly with the greatest of ease. It can stay aloft for very long periods of time (2), with such slow, effortless wing beats that the sequence of wing movements is easy to observe (3).

Endemic to Sri Lanka, the Ceylon tree nymph tends to occur in forests below 2,000 feet, but may be found at altitudes of up to 5,000 feet (3).

The Ceylon tree nymph is found in wet evergreen forests, where it spends most of its time high in the tree canopy. Some colonies are also found in tall forests beside rivers in the dry zone (3).

Although the Ceylon tree nymph spends much of its time flying leisurely high in the tree canopy, it does descend to the ground to feed on nectar and to breed (3). During courtship, males and females fly together for a long period and the male extends two brush-like organs (known as hair pencils) from the tip of his abdomen. These hair pencils brush against the female’s antennae and release pheromones and other chemicals that stimulate her to mate (4). One of these chemicals, danaidone, is poisonous, and is also passed to the female with the sperm during mating. This substance is gathered by the adult males from various plants and deters predators from eating the butterflies. Some of the danaidone passed to the female from the male during mating ends up in the tissues of the female and in her eggs, protecting both the female and the eggs from predation (4).

The main threats facing the beautiful Ceylon tree nymph are destruction and degradation of its habitats (5).

This species is classified as Near Threatened by the IUCN Red List. As yet, direct conservation action has not been targeted at this species, although it does occur in a number of protected sites, including the forest reserves of Kanneliya, Sinharaja and Morapitiya (5) (6).

View information on this species at the UNEP World Conservation Monitoring Centre.

Find out more on the Ceylon tree nymph:

• Sri Lankan Insects:
  http://www.srilankaninsects.net/Butterflies/Danaidae/CeylonTreeNymph/CeylonTreeNymph.htm
• Gehan' s Guide to the Birds, Butterflies and Dragonflies of Sri Lanka by Gehan de Silva Wijeyeratne (In prep – available 2005):
  http://www.jetwingeco.com/