Lord Howe Island stick insect (Dryococelus australis)

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Lord Howe Island stick insect, anterior view
IUCN Red List species status – Critically Endangered CRITICALLY
ENDANGERED

Top facts

  • The Lord Howe Island stick insect is a large, flightless insect named after Lord Howe Island, where it was originally found.
  • The accidental introduction of predatory rats to its habitat caused the disappearance of the Lord Howe Island stick insect on Lord Howe Island.
  • The Lord Howe Island stick insect currently only survives on a tall rocky outcrop known as Ball’s Pyramid, several kilometres away from Lord Howe Island.
  • The robust, heavy body of the Lord Howe Island stick insect has earned it the alternative name of ‘land lobster’.
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Lord Howe Island stick insect fact file

Lord Howe Island stick insect description

KingdomAnimalia
PhylumArthropoda
ClassInsecta
OrderPhasmida
FamilyPhasmatidae
GenusDryococelus (1)

A large, flightless insect (2), the Lord Howe Island stick insect (Dryococelus australis) is also known as the ‘land lobster’ or ‘tree lobster’ (3) because of its robust, heavy body (1) (2) (3). This species was once thought to have become extinct, until a small population was unexpectedly discovered in a previously unknown location (1) (3).

The Lord Howe Island stick insect is dark golden-brown in colour, and is marked with a conspicuous cream stripe which runs along its abdomen. Males of this species tend to have longer and thicker antennae than the females, as well as a narrower abdomen and spiny, much larger hind legs (2).

Juvenile Lord Howe Island stick insects, known as nymphs (4), are bright green (2) (3) (5), and begin to change to the adult colouration at a few months old (3).

Also known as
land lobster, Lord Howe Island phasmid, Lord Howe Island stick-insect, tree lobster.
Size
Male length: up to 10.6 cm (2)
Female length: up to 12 cm (2)
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Lord Howe Island stick insect biology

Whereas adult Lord Howe Island stick insects are typically nocturnal (1) (2) (4) (5), juveniles of this species tend to be active by day (2) (5). As with all other stick insects, the Lord Howe Island stick insect is a herbivorous species (5). It has been recorded feeding on a variety of plants (5), although on Ball’s Pyramid it is only known to feed on the leaf tips of one species of shrub, Melaleuca howeana (2) (4) (5). In captivity, adult Lord Howe Island stick insects feed on tree lucerne (Cytisus proliferus) and fig species, but juveniles tend to eat bramble (5).

Interestingly, as well as reproducing sexually, the Lord Howe Island stick insect is thought to be able to reproduce asexually (3) by parthenogenesis, whereby unfertilised eggs hatch into females (2). Mating in this species is reported to occur up to 3 times per night and may take up to 20 minutes each time (5). The female Lord Howe Island stick insect lays batches of eggs in the soil and buries them using the underside of her abdomen (2) (3) (5). Each batch typically contains about ten eggs (5), which are beige and patterned with raised, reticulated markings (2). Batches are laid at intervals of about 7 to 10 days (5), and each female Lord Howe Island stick insect can produce up to 300 eggs during its lifetime (3).

Young Lord Howe Island stick insects moult as they grow, eventually getting darker and becoming an adult at about seven months of age (5). The lifespan of the Lord Howe Island stick insect is thought to be about 12 to 18 months (3).

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Lord Howe Island stick insect range

The Lord Howe Island stick insect is endemic to the Lord Howe Island Group off the coast of mainland Australia (2), and was originally thought to be confined to Lord Howe Island itself (1) (2) (5). Once abundant (2), this species was believed to have unfortunately been driven to extinction following the accidental introduction of rats to the island in 1918 (1).

However, a small population of Lord Howe Island stick insects was later discovered on Ball’s Pyramid, a tall volcanic outcrop 23 kilometres away from Lord Howe Island (1) (5).

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Lord Howe Island stick insect habitat

In its original habitat on Lord Howe Island, the Lord Howe Island stick insect was known to be found in forested areas, sheltering in large hollows within living tree trunks (1) (2). However, there are no trees present on Ball’s Pyramid (1) (2), and in this area the Lord Howe Island stick insect occurs on a single plant species (5), Melaleuca howeana, which is the only species of shrub present on the rocky stack (2). The Lord Howe Island stick insect is reported to shelter within cavities formed by the accumulation of debris from the shrubs, and is only known to occur in an area of 180 square metres (2).

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Lord Howe Island stick insect status

The Lord Howe Island stick insect is classified as Critically Endangered (CR) on the IUCN Red List (1).

IUCN Red List species status – Critically Endangered

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Lord Howe Island stick insect threats

The reason for the Lord Howe Island stick insect’s disappearance from its original habitat on Lord Howe Island was predation by rats, which were accidentally introduced to the island in 1918 (1) (2) (3) (4).

Several factors may currently threaten the remaining population of the Lord Howe Island stick insect on Ball’s Pyramid, including habitat disturbance and illegal collection. The shrub species on which it depends is also disappearing as a result of competition with other plants such as morning glory (Ipomoea cairica) (3). In addition, given the extremely small size of the wild population, estimated at about 20 to 30 individuals (4), the Lord Howe Island stick insect is at risk of being completely wiped out by one random event (3).

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Lord Howe Island stick insect conservation

Access to the Lord Howe Island stick insect’s habitat on Ball’s Pyramid is tightly controlled and restricted to help protect the environment (3). This species is listed as Critically Endangered in New South Wales under the Threatened Species Conservation Act 1995 (2).

A captive breeding programme at Melbourne Zoo is currently playing an important role in the future survival of the Lord Howe Island stick insect (4). Intensive research is being conducted at the zoo into the species’ diet, behaviour and biology, and this information has helped to bring the species back from the brink of extinction (3) (4). Since a pair of Lord Howe Island stick insects was given to Melbourne Zoo at the beginning of 2003, the captive population has thrived (5), with more than 9,000 individuals having been bred at the facility, many of which have been sent to other institutions around the world for breeding purposes (3).

The main objectives of the Melbourne Zoo captive breeding programme are to raise awareness of the plight of the Lord Howe Island stick insect, maintain an ‘insurance’ population in captivity (3) (4), and ultimately to reintroduce the species to Lord Howe Island once rats have been completely eradicated from the area (3) (4) (5).

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

Find out more about the Lord Howe Island stick insect and its conservation:

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Authentication

This information is awaiting authentication by a species expert, and will be updated as soon as possible. If you are able to help please contact:
arkive@wildscreen.org.uk

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Glossary

Abdomen
In arthropods (crustaceans, insects and arachnids) the abdomen is the hind region of the body, which is usually segmented to a degree (but not visibly in most spiders). In crustaceans (such as crabs), some of the limbs attach to the abdomen; in insects the limbs are attached to the thorax (the part of the body nearest to the head) and not the abdomen.
Antennae
A pair of sensory structures on the head of invertebrates (animals with no backbone).
Asexual reproduction
Reproduction that does not involve the formation of sex cells (‘gametes’). In many species, asexual reproduction can occur by existing cells splitting into two, or part of the organism breaking away and developing into a separate individual. Some animals, including vertebrates, can also develop from unfertilised eggs; this process, known as parthenogenesis, gives rise to offspring that are genetically identical to the parent.
Endemic
A species or taxonomic group that is only found in one particular country or geographic area.
Herbivorous
Having a diet that comprises only vegetable matter.
Moult
In insects, a stage of growth whereby the hard outer layer of the body (the exoskeleton) is shed and the body becomes larger.
Nocturnal
Active at night.
Nymph
Stage of insect development, similar in appearance to the adult but sexually immature and without wings. The adult form is reached via a series of moults, and the wings develop externally as the nymph grows.
Parthenogenesis
The development of offspring from unfertilised eggs. The individuals that results are usually genetically identical to their mother.
Reticulated
Marked with a criss-cross or network-like pattern.
Unfertilised
An unfertilised egg is one which has not been fertilised; that is, it has not fused with a male gamete (reproductive cell).
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References

  1. IUCN Red List (October, 2013)
    http://www.iucnredlist.org/
  2. Department of Sustainability, Environment, Water, Population and Communities (2013) Dryococelus australis. In: Species Profile and Threats Database. Department of Sustainability, Environment, Water, Population and Communities, Canberra. Available at:
    http://www.environment.gov.au/cgi-bin/sprat/public/publicspecies.pl?taxon_id=66752
  3. Zoos Victoria’s 20 Priority Species - Lord Howe Island stick insect (October, 2013)
    http://www.zoo.org.au/sites/default/files/lord-howe-island-stick-insect-priority-species.pdf
  4. Melbourne Zoo - Lord Howe Island stick insect (October, 2013)
    http://www.zoo.org.au/melbourne/animals/lord-howe-island-stick-insect
  5. Natural History Museum - Dryococelus australis (October, 2013)
    http://www.nhm.ac.uk/nature-online/species-of-the-day/biodiversity/endangered-species/dryococelus-australis/index.html
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Image credit

Lord Howe Island stick insect, anterior view  
Lord Howe Island stick insect, anterior view

© Rohan Cleave Melbourne Zoo

Judith Henke
Communications Manager
Melbourne Zoo, Elliott Avenue
Parkville VIC 3052.
Australia
Tel: 03 9285 9487
jhenke@zoo.org.au
http://www.zoo.org.au/

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