Cook Strait giant weta (Deinacrida rugosa)
|Also known as:||Stephens Island weta|
|Size||Length: up to 7 cm (2)|
Male weight: 14 g (2)
Female weight: 27 g (2)
Classified as Vulnerable (VU) on the IUCN Red List (1).
Reaching up to an enormous seven centimetres in length, the Cook Strait giant weta is one of the largest insects in the world (3) (4). Its scientific name Deinacrida, meaning “terrible grasshopper”, is an apt description for this fearsome-looking species (4). The brownish-yellow body is bulky and heavily armoured, with the upper surface covered by a series of thickened, overlapping plates, which have black markings (2) (4). Relative to the size of the head, the jaws are large (5), and the elongated hind legs have five or six large spines, and can be raised above the head in defence (2) (4). The female is significantly larger than the male, and both sexes lack wings (5) (6).
Endemic to New Zealand, the Cook Strait giant weta is found on the islands of the North, South and Middle Trio, Stephens, Maud, Matiu-Somes and Mana (2). In 2007, this species was reintroduced to mainland New Zealand, where it had been extinct for over 100 years, and is now found in Karori Wildlife Sanctuary on North Island (4).
The Cook Strait giant weta occupies open grassland, shrubland and forest margins (2) (7).
Despite its menacing appearance, the Cook Strait giant weta is reasonably docile, mostly feeding on plants, and tolerating gentle handling by humans (6). A nocturnal species, during the day the Cook Strait giant weta conceals itself amongst grass in a temporary refuge that it makes in the soil surface, or under dead leaves, bark or stones (2) (4). It emerges just after dusk, foraging on the ground or on low-growing bushes and shrubs, where it particularly favours tauhinu flowers (Cassinia leptophylla) (2).
Owing to its solitary and nomadic lifestyle, the Cook Strait giant weta’s reproduction relies upon the male locating a receptive female. This search is facilitated by the strong scent produced by the weta’s body and by its faecal pellets (4) (6), and can involve the male travelling over 250 metres in a single night (4) (8). Once located, the male places a leg over the female’s body and maintains contact until a daytime refuge is found. Here, mating occurs throughout the day and, if the weather is cool and wet, possibly throughout the night as well (8). The female subsequently lays around 200 eggs in the soil and dies. The eggs develop for a few months and hatch in the spring, with the juvenile wetas emerging fully-developed. It takes most of the Cook Strait giant weta’s two year lifespan to reach the full adult size, with growth taking place in a series of about nine moults over a 12 to 18 month period (4).
A number of animals prey on the Cook Strait giant weta, including birds (7), and reptiles such as the tuatara (6). As a defence against predators the Cook Strait giant weta will raise its spiked legs over its head and wave them up and down while making a hissing sound by rapidly rubbing together the overlapping plates on its upper body (5).
Historically, the Cook Strait giant weta was found on mainland New Zealand as well as many off-shore islands, but the introduction of mammalian predators such as the black rat (Rattus rattus), and the clearance of much of its habitat, led to the contraction of its range to just a few small, “rat-free” islands in the Cook Strait (7). A combination of its ground-dwelling lifestyle, large size, and strong scent make it particularly vulnerable to predation, and therefore, accidental introductions of mammalian predators to the offshore islands could be catastrophic for its survival (6).
Introductions of the Cook Strait giant weta to Mana Island in 1976, Matiu-Somes Island in 1996, and, most recently, Karori Wildlife Sanctuary on North Island in 2007 have helped to greatly expand this Vulnerable species’ range. In addition, on Mana Island, the removal of cattle and eradication of mice has dramatically increased the Cook Strait giant weta’s abundance. With the success of these introductions, the New Zealand Department of Conservation plans to continue to introduce the Cook Strait giant weta to new island habitats, while ensuring that its existing island habitats remain protected against the threat of predator invasion (7).
One of the most exciting developments in the conservation of this species has been its introduction to Karori Wildlife Sanctuary. By using a specially-designed fence to exclude mammalian predators, the sanctuary hopes to re-establish an environment similar to that which existed on New Zealand before the arrival of humans, where species such as the Cook Strait giant weta can thrive once more (9).
For more information about the conservation of the Cook Strait giant weta see:
- Karori Sanctuary:
- New Zealand Department of Conservation:
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- Endemic: a species or taxonomic group that is only found in one particular country or geographic area.
- Moults: in insects, referring to stages of growth, whereby the hard outer layer of the body (the exoskeleton) is shed and the body becomes larger.
- Nocturnal: active at night.
- Nomadic: a species which roams irregularly from place to place in search of food and water, without returning to a fixed location.
IUCN Red List (December, 2009)