|Scientific Name:||Dryococelus australis (Montrouzier, 1855)|
Eubulides spuria Kirby, 1904
Karabidion australe Montrouzier, 1855
|Taxonomic Source(s):||Brock, P.D. 2015. Phasmida Species File Online. Version 5.0/5.0. Available at: http://Phasmida.SpeciesFile.org. (Accessed: 29 May 2015).|
|Red List Category & Criteria:||Critically Endangered D ver 3.1|
|Assessor(s):||Rudolf, E. & Brock, P.|
The Lord Howe Island Stick-insect (Dryococelus australis) was thought to have become Extinct around 1920 after the introduction of rats to Lord Howe Island. However, in 2001 the species was rediscovered on Balls Pyramid, a rocky outcrop 23 km from Lord Howe Island. The species persists within an area of less than 1 km² on Balls Pyramid, with a maximum observed population size of only 35 individuals. Although the exact condition of the species’ habitat on Balls Pyramid is unknown due to only occasional surveys for the reason of minimising the impact on this vulnerable habitat, it is well protected and thus not believed to be declining. However, any coincidental event negatively affecting the species’ habitat could lead to the extinction of the wild population of this highly threatened species. The Lord Howe Island Stick-insect is therefore assessed Critically Endangered under criterion D.
|Previously published Red List assessments:|
The Lord Howe Island Stick-insect was previously thought to be endemic to the Lord Howe Island, Australia. After the accidental introduction of rats (Rattus rattus) in 1918, the species disappeared from the island within a few years and was thus believed to be extinct. However, in the 1960s, large stick insects were reported to exist on Balls Pyramid, a rocky outcrop 23 km away from Lord Howe Island (Smithers 1969). A scientific expedition to the rock in 2001 confirmed that this stick insect is Dryococelus australis (Macey 2001). The population on Pall’s Pyramid is confined to a few Melaleuca howeana plants on the north-west face of the otherwise rocky island featuring only groundcover (Priddel et al. 2003). This area only has an extent of about 30 by 10 m (Honan 2008). The species’ extent of occurrence and area of occupancy are accordingly both estimated to be 4 km² although the actual area occupied by this species is 300 m². Due to the very small distribution, any disturbance of the species’ habitat could drive the species to extinction. Therefore, the number of locations is inferred to be only one.
|Range Map:||Click here to open the map viewer and explore range.|
At the first census in 2002, only 24 specimens were reported on Balls Pyramid (Priddel et al. 2003). Monitoring of the wild population has since revealed a fluctuation between 9 to 35 adult individuals (Carlile et al. 2009).
|Current Population Trend:||Unknown|
|Habitat and Ecology:||Dryococelus australis is a large, heavy-bodied species (Gurney 1947). On Lord Howe Island the species was found in large cavities in the trunks of living trees, emerging at night to feed (Lea 1916). However, Balls Pyramid is a small, desolate, rock island without trees. The habitat of the species on this island consists in a few Melaleuca howeana shrubs situated on a single terrace. They are likely to use a single accumulation of moist vegetation as a daytime refuge (Priddel et al. 2003).|
|Continuing decline in area, extent and/or quality of habitat:||No|
|Movement patterns:||Not a Migrant|
|Use and Trade:||The species is not utilised.|
The very small population size of the species as well as the very restricted distribution makes the Lord Howe Island Stick-insect highly sensible to any random stochastic event. As the only suitable habitat for the species on Balls Pyramid consists in a few Melaleuca shrubs on only one terrace of the island, any disturbance of the habitat and any threat to those shrubs could seriously threaten the species’ survival. Besides climatic variables like droughts and storms, the occurrence of an invasive vine species (Ipomoea cairica) could lead to the death of the species’ food plants and thus potentially the extinction of the wild population of the species. Furthermore, a removal of this rare species from the wild due to a potential poaching by insect collectors could lead to a collapse of the small population on Balls Pyramid (Priddel et al. 2003).
Based on two founder pairs, an ex-vito breeding program was established. Today, about 700 individuals and thousands of eggs exist in the Melbourne Zoo, and additional breeding programs were initiated in the zoos of San Diego, Toronto and Bristol. Furthermore, a removal of the Ipomoea cairica plants close to the species’ habitat was conducted in 2003. An ongoing rodent eradication program is in place on Lord Howe Island. As soon as this is completed, a reintroduction of the Lord Howe Island Stick-insect into its original habitat is targeted. Balls Pyramid is preserved as part of the Lord Howe Permanent Park Preserve, granting only access for scientific purposes.
|Citation:||Rudolf, E. & Brock, P. 2017. Dryococelus australis. The IUCN Red List of Threatened Species 2017: e.T6852A21426226.Downloaded on 25 June 2018.|
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