Background and Significance.
The Lord Howe Island Phasmid (Dryococelus australis) is large, flightless, impressive in size and appearance and is probably the rarest insect in the world, as few as 20 D. australis may still survive in the wild on an isolated rock pinnacle- Ball’s Pyramid, 23km South-East of Lord Howe Island and separated by a deep underwater trench. The pyramid itself, is an eroded volcano produced by volcanic eruptions some 7 million years ago, it consists of only 1455 ha, is isolated, lying approximately 793km from Australia, 975km from New Zealand and 1000km from Norfolk Island. This rarity and isolation of D. australis makes all aspects of its biology of great scientific interest.
In February 2001 a team of scientists arrived on Lord Howe Island for the purpose of resolving the mystery of the Lord Howe Island Phasmid. Ball’s Pyramid is believed to be the last place the Phasmid might have survived. A search for the presence of the long extinct Lord Howe Island Phasmid (stick insect) was therefore undertaken at this location. On a number of occasions the rock has been scaled and searched by numerous scientists and climbers (Hutton, 1998).
D. australis is locally known as the “land lobster” this species was found all over Lord Howe Island. No live specimens of the Phasmid have been seen since the 1920s. Lea (1916) gives a brief account of its habits with very little known about its biology or ecology, describing it as nocturnal, spending the days in tree hollows, often those made by longicorn beetles, with up to 68 individuals in a single hollow. Large amounts of frass (“several bushels”) would develop beneath a single tree. Eggs and eggshells were found in the frass indicating that, D. australis like most Phasmids, release their eggs from above the ground? The eggs have not yet been described and there is no published account of a host food plant (Priddel et al 2003).
HMS Supply first sighted Lord Howe Island on the 17th February 1788. The colony was established some 45 years later and in 1918 rats were accidentally introduced after the sinking of the Makambo. Within a very short time D. australis was eradicated. From the mid 60’s a number of climbers (David Roots (1965) & Dick Smith (1979)) to Balls found the remains of Phasmids which opened the gates to speculation that the Phasmid may have survived, even in such a remote and harsh environment. The vegetation is limited, and all attempts to find these creatures had failed. The main objective of the our first survey (2001) was to find D. australis and then if a population existed obtain information on the following; Population size; Distribution; Threats to its survival and Vulnerability to disturbance. A search of Gannet Green resulted in finding no suitable vegetation, the survey team moved down approximately 50 metres, where searching through the leaf litter around and under a tee-tree, found several droppings and two eggs. This meant that the stick insect was here!
Phasmids the world over usually feed at night, the only way to really know if it was there, was to search at night. The two most experienced climbers in the team, climbed the 100 metres at night up almost sheer cliffs, climbed up the escarpment and after a long and arduous night climb reached the desired point. Nicholas then yelled there's one, as Dean was looking at another one at the same time. After the odd 70 years the Lord Howe Island Phasmid was rediscovered.
A second survey of the terrace where D. australis were found in February 2001 was surveyed again on the night of 26th March 2002. This 2nd survey, located a total of 24 live D. australis. All individuals were located on the outer foliage of Melaleuca howeana shrubs where they were apparently grazing on the new leaf tips. Twelve individuals were found on the same shrub where the three individuals were discovered the previous year. The other 12 individuals were dispersed among five nearby, smaller shrubs. All six shrubs occupied by D. australis were within an area of about 30 m by 6 m, and several contained the nests of Common Noddies. The extremely unstable nature of the scree made it hazardous to approach, consequently, not all individuals could be viewed close-up, and of the 24 D. australis seen, only 10 could be positively sexed—eight females and two males. These were the first males of this species to be recorded on Balls Pyramid.
In 2003 two females and two males were removed from Balls Pyramid to establish a captive breeding program. One pair was taken to Melbourne Zoo and the second pair were taken by a private insect breeder (Insektus) where there are now 7 nymphs from 21 eggs laid by the original pair. The nymph’s range in size (February 04) from 6.5 to 8.5 cm they are healthy and come out each night to feed on the tea -tree.
In February 2003, two females and two males were removed from the wild to set up breeding colonies, one pair in NSW under the care of Stephen Fellenberg (Insektus), the other at Melbourne Zoo. Both pairs laid eggs with the NSW pair only living for approximately 6 weeks, but laying 21 eggs From these 21 eggs, seven nymphs survive ranging in size from 6.5 to 8.5cm (February 2004). Studies of these nymphs form the basis for this Masters project described in this application.
“One of the most remarkable species of insects that I obtained during a recent (December, 1915, and January, 1916) visit to Lord Howe Island is a large wingless phasma, Karabidion (formerly Eurycantha) australe, Montr. It appears to have been taken by almost every natural history visitor to the island, and, in fact, once their hiding-places are known, specimens may be taken in practically unlimited numbers. During the day they remain concealed in hollows in upright or slightly sloping stems of living trees, but their presence may be detected by examining the ground at the foot of the trees, where heaps of their excrement, sometimes amounting to bushels, may be found. The hollows are seldom less than eighteen inches in length, and are sometimes much longer; suitable ones are probably used for years. On examining the heaps of droppings, frequently both fresh and newly-hatched eggs may be found, the females apparently simply extruding their eggs as soon as these are ready” (Lea, 1916).
Worldwide, there are about 0.75–1 million known species of insect (class Insecta) (IUCN 1983), of which 72 species are currently regarded as extinct (IUCN 2000). The majority of these extinct insects came from island communities, particularly those that exhibited a high degree of endemism. Globally the principal causes of insect extinctions include deforestation, changes to aquatic environments, atmospheric pollution, loss of hosts, the introduction of exotic plants and animals, over-collecting and the use of pesticides (IUCN 1983). The largest of the extinct insects is the Lord Howe Island Stick-Insect (D. australis (Montrouzier)).
Conservation of this species should have a high priority. There are a number of issues that will follow from this study, namely the establishment of the breeding population on LHI- dependent on knowing their biology and behaviour, the threat of the weed, morning glory Ipomoea cairica, the removal of the rat population, and the most difficult issue to confront will come from us (humans) perception of insects as just bugs or pests. This species is not a pest and during the course of this project one of the major outcomes will be to high light the species vulnerability and the importance of insect (invertebrate) conservation.
The above photograph was taken by Nicholas Carlile, and the full acticle of the rediscovery can be found in Biodiversity and Conservation 12:1391 -1403, 2003. David Priddel et al.