Christmas Emperor - Polyura andrewsi | image courtesy Max Orchard
The inventory of the invertebrate fauna, which has several hundred collected specimens still awaiting identification, has described 14 snails, 28 butterflies, some 70 moths, 90 beetles, 30 spiders, one scorpion, five false scorpions and one amphilicid.
By 1900, naturalists had found only nine species of butterfly on Christmas Island, excluding the three skippers. This included one endemic species (Christmas Island Emperor), two endemic subspecies (Climena Crow and Scalloped Grass-Yellow) and one vagrant (Evening Brown). By 2006 the list had grown to include 28 species. Some of the additions since 1900 are species only recorded very rarely (i.e. vagrants) and some may have been present for much longer but were overlooked in the early days. However, the vast majority are now established and they feed only on introduced plants that have become established in cleared and disturbed habitats. Whether these butterflies arrived unassisted (i.e. flew in as adults from Asia) or came as larvae in shipments of supplies to the island is unknown.
Most of the resident butterfly species on the island are common. The endemic subspecies of Climena Crow and Scalloped Grass-Yellow are abundant in open habitats and also occur inside the forest. The Christmas Emperor is a rainforest canopy species and is therefore difficult to observe. It is sometimes seen floating over the canopy along the roads and tracks or the plateau.