Lord Howe Island Stick Insect (Dryococelus australis) Fact Sheet: Summary

Kingdom: Animalia

Phylum: Arthropoda

Class: Insecta

Order: Phasmida — stick and leaf insects

Family: Phasmatidae

Genus: Dryococelus

Species: Dryococelus australis — Lord Howe Island stick insect, “tree lobster”
 

Synonyms
Eubulides spuria, Eurycanta australis, Karabidion austral

Sources: Westwood (1859), Etheridge (1889), Priddel et al. (2003), Rudolf and Brock (2017)

Body Length

Up to approximately 130 mm (5.1 in) (Lea 1916; Shi et al. 2019). Gurney (1947) reports males as smaller than females.

General Appearance

Body smooth and glossy (Westwood 1859; Honan 2008). Head square-shaped (Westwood 1859). No wings (Cassis 2017).

Adult males have 2 large spines on enlarged hind femur (Gurney 1947; Zompro 2001). Females have a wider, tapered abdomen and ovipositor on last abdominal segment (Honan 2008; Cleave 2013). Antennae longer and thicker in males (Lea 1916; Gurney 1947).

Coloration

Adults dark golden-brown to black, often with a reddish-brown tint. Lateral line stripe cream colored. Hatchlings bright green; darken with each molt stage (Westwood 1859; Gurney 1947; Priddel et al. 2003; Carlile et al. 2009; Cleave 2013). Juveniles brown to dark brown (Honan 2008).

Range

Known to 2 small islands east of mainland Australia: Lord Howe Island (580 km, or 360 mi, east of mainland Australia) and Ball’s Pyramid (an islet 23 km, or 14 mi, from Lord Howe Island) (Priddel et al. 2003; Carlile et al. 2009; Rudolf and Brock 2017; Flemons et al. 2018).

Extinct in the wild on Lord Howe Island (Rudolf and Brock 2017). Reintroductions planned; will begin after invasive rodent eradication monitoring efforts are complete (implemented in 2019) (Honan 2008; Carlile et al. 2009; Priddel and Carlile 2010; Flemons et al. 2018; NSW Government 2021).

Remaining wild population restricted to a group of tea tree shrubs (Melaleuca howeana) on the northwest face of Ball’s Pyramid (300 m², or 3,000 ft²).

Elevation range: 110–500 m (360–2,000 ft) (Flemons et al. 2018)

Habitat

Tea tree (Melaleuca howeana) shrubs on island cliff faces and terraces on Ball’s Pyramid (Flemons et al. 2018); no other suitable habitat (shrubs or trees) on Ball’s Pyramid (Honan 2008; Cassis 2017; Rudolf and Brock 2017). Also found in cavities formed by accumulated plant debris (Priddel et al. 2003), among rocks, and in rocky crevices (Flemons et al. 2018).

Etheridge (1889) and Lea (1916) state forested areas, specifically tree trunk cavities, to be D. australis’ primary habitat on Lord Howe Island. Potential host plants investigated by McGrath et al. (2017). Nymphs and adults likely prefer different host plant species (McGrath et al. 2017).

High humidity appears crucial to survival (e.g., Honan et al. 2007); however, not yet investigated for wild populations.

IUCN Status

Critically Endangered (2017 assessment) (Rudolf and Brock 2017)

CITES Appendix

Not listed (UNEP 2021)

Other Designations

Critically Endangered under Australia’s Environment Protection and Biodiversity Conservation Act (2002 assessment) and New South Wales’ Biodiversity Conservation Act (2021 assessment) (SPRAT 2021).

Lord Howe Island is a UNESCO-designated World Heritage site (Cassis 2017). Ball’s Pyramid is part of the Lord Howe Permanent Park Preserve (Rudolf and Brock 2017).

Populations in the Wild

Once abundant on Lord Howe Island (Honan 2008). Previously thought to have gone extinct by 1930, after black rats (Rattus rattus) accidentally introduced to Lord Howe Island in 1918 (Gurney 1947; Nicholls 1952; Paramonov 1963; Priddel et al. 2003; Carlile et al. 2009; Cleave 2013; Wilkinson 2014). Fresh remains discovered in 1964 on nearby Ball’s Pyramid (Smithers 1969; McAlpine 1996 as cited by Priddel et al. 2003). In 2001 and 2002, more than 20 live individuals observed (Priddel et al. 2003; Mikheyev et al. 2017).

Single wild population of fewer than 40 individuals on Ball’s Pyramid (Rudolf and Brock 2017). Large genome; considerable genetic variability retained in Ball’s Pyramid population (Mikheyev et al. 2017).

At risk of extinction in the wild due to small population size and negative impacts to restricted habitat area (Rudolf and Brock 2017). Unsampled habitat remains on Lord Howe Island and Ball’s Pyramid, but populations still thought to be small (Flemons et al. 2018). Rainfall and humidity may contribute to inter-annual fluctuations in population size (Priddel et al. 2003; Carlile et al. 2009) and sex ratios (Flemons et al. 2018).

Threats to Survival

Invasive animals (e.g., rodents, cockroaches). Loss of food plants due to plant diseases, invasive plants (morning glory), and chemical sprays used to control spread of invasive plants (Priddel et al. 2003; Carlile et al. 2009; Rudolf and Brock 2017; Flemons et al. 2018). Harsh weather and climate conditions (e.g., storms, drought), landslides, and other random stochastic environmental events (Cleave 2013; Rudolf and Brock 2017). Potential poaching by insect collectors, though access to Ball’s Pyramid is tightly controlled by the Lord Howe Island Board (Priddel et al. 2003).

Activity Cycle

Adults hide during the day in tree hollows, rock crevices, and vegetation. Emerge at night to feed (Lea 1916; Flemons et al. 2018). Cleave et al. (2013) describe young insects as diurnal and adults as nocturnal.

Activity occurs in bursts (up to 5 minutes), followed by a rest period (Priddel et al. 2003; Honan et al. 2007).

Social Behavior

Little known. Lea (1916) and Honan (2008) observed many individuals of different age classes using the same sheltering spaces. Nymphs and juveniles in managed care cluster together during the day (Honan et al. 2007; Ellis 2017).

Diet and Feeding

On Ball’s Pyramid, eat leaves from Melaleuca howeana and possibly other plants. Observed chewing bark (Honan et al. 2007; Honan 2008). See Honan et al. (2017) for feeding description.

Former diet on Lord Howe Island, prior to extirpation, not known (Honan 2008; SPRAT 2021) — but see McGrath et al. (2017).

Reared on a range of plants in managed care (e.g., Honan et al. 2007).

Predators

Lord Howe Island: historically, rats (e.g., Priddel et al. 2003) and probably owls (introduced and native species) (Wilkinson 2014).

Ball’s Pyramid: not reported

Locomotion

Wingless stick insect; does not fly (Cassis 2017). Walks forward and backward (Honan et al. 2007). Typically moves slowly — unless perceives a threat, then moves quickly to refuge (Priddel et al. 2003; Honan et al. 2007). Adept climber; can descend vertical surfaces head-down and cross underside of horizontal surfaces (Honan et al. 2007; Flemons et al. 2018). Nymphs move “in a jerky fashion” (Honan et al. 2007).

Conservation History

Successful breeding programs in managed care. Most successful program at Melbourne Zoo (established 2003). Thousands of individuals bred, primarily from one surviving founder pair from Ball’s Pyramid named “Adam and Eve” (Priddel et al. 2003; Honan 2007; Honan 2008; Carlile et al. 2009; Cleave 2013; Wilkinson 2014; Rudolf and Brock 2017). Additional breeding programs established in Australia (including Lord Howe Island), Europe, and North America (San Diego Zoo Wildlife Alliance) (Carlile et al. 2009; Priddel and Carlile 2010; Cleave 2013).

Sexual Maturity

Reach adult size at approximately 210 days, on average (range 201–224 days) (Honan et al. 2007). Females begin laying eggs about 14–16 days after final molt (Honan et al. 2007; Honan 2008; Carlile et al. 2009).

Mating

Observed only in managed care. Takes place on the ground or while hanging vertically. Male mounts female and curls abdomen tip to insert copulatory organ into female’s abdomen. Pair remains motionless. Mating lasts 15–25 min, with up to 3 bouts per night (Honan et al. 2007). Mate choice may play a role in egg hatching success; confirmation needed (Lambert 2012; M. Elgar, personal communication, 2021).

Eggs and Egg Laying

Eggs ellipsoid in shape; capsule-like. About 4 x 6 mm (0.1 x 0.2 in). Whitish to cream-colored but darken when exposed to moisture. Females reported to lay up to 250–300 eggs during life span (Priddel et al. 2003; Honan et al. 2007; Honan 2008).

Female deposits eggs about 2.5 cm (1.0 in) deep in soil (or other substrate provided in managed care). Female smooths soil surface with abdomen after laying.

Clutch Size

Typically 9–10 eggs, though smaller clutches and single eggs also laid (Honan et al. 2007; Honan 2008). Also see Flemons et al. (2018).

Interclutch Interval

7–10 days (Honan 2008)

Incubation Period

About 6–9 months in managed care (Cleave 2013). Honan (2008) states an average of 209 (range: 175–241) days.

Hatching

Weight at hatching: approximately 0.6 g (0.2 oz) (Honan 2008)

Length at hatching: approximately 20 mm (0.8 in) (Honan et al. 2007; Honan 2008)

Nymphs emerge underground, burrow to surface, and climb to reach safety (Honan et al. 2007).

Growth

An estimated 5 instars between egg and adult life stages. Intermolt period varies but may be as little as 10 days for later instars (Honan et al. 2007).

Typical Life Expectancy

Wild populations: not known
Managed care: no AZA estimates

Feature Facts

• One of the world’s rarest and most critically endangered invertebrates (Priddel et al. 2003; Cassis 2017; Flemons et al. 2018)
• International media coverage following the species’ rediscovery in 2001 raised the profile of invertebrate conservation in Australia (Honan 2008)
• San Diego Zoo Wildlife Alliance has a long-time conservation partnership with the Melbourne Zoo, the first organization to successfully breed this species (in 2003)
• In 2016, female Lord Howe Island stick insects at the San Diego Zoo laid eggs — a first for any North American breeding program (San Diego Zoo Global Public Relations 2016)
• Lord Howe Island stick insects collected in large numbers in the early 1900s, prior to local extirpation on Lord Howe Island (Priddel et al. 2003; Honan 2008)
• Said to have been historically used as bait by Lord Howe Island fishers (Cleave 2013). Not known how the species dispersed to Ball’s Pyramid; possibly transferred by fishers (Honan 2008) or nesting seabirds (SPRAT 2021).
• Evolutionarily unique; this species comprises a separate lineage from other Australasian stick insects that predates the formation of Lord Howe Island (see Buckley et al. 2009; Buckley et al. 2010)