Conservation status: Threatened - Nationally Critical
Found in: Mahoenui Giant Wētā Scientific Reserve and three other North Island sites
Threats: Fire, predation
In 1962 a population of giant wētā were discovered in remnant patches of tawa forest at Mahoenui in the southern King Country. More wētā were found on farmland reverting to gorse in 1987.
It's likely that the wētā were once present throughout the lowland forests of Waikato.
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Description
Mahoenui giant wētā lay their eggs by pushing their ovipositor (egg laying tube) into the ground, They lay small groups of up to 100 eggs which develop in the ground and hatch only when the weather warms up, which can take up to 10 months.
Newly hatched wētā are called nymphs. It takes up to two years for the wētā to reach adulthood.
The wētā range in size. Females are larger than males, with female adults measuring up to 75 mm and adult males 50 mm. Females weigh up to 19 g (the same weight as a mouse) and males up to 12 g.
Mahoenui giant wētā are unique amongst the giant wētā species in having two different colour morphs. Although most tend to be a dark brown mahogany colour, a third of them are a lovely yellow, and one female was even discovered with mahogany for half of her body and the other side yellow.
Mahoenui Giant Wētā Scientific Reserve
DOC purchased the land at Mahoenui where giant wētā was discovered and turned it into a reserve for the wētā .
The vegetation in the reserve is mainly gorse. While gorse is considered a pest thoughout New Zealand, in this reserve it's an important plant as it provides protection from predators such as rats, hedgehogs and possums. Without this protection, the wētā is highly vulnerable to introduced predators.
Wild goats browsing on the gorse help to maintain its regrowth and are important in protecting the wētā. It's the only reserve in the country where gorse and goats are protected.
Threats
The main threats to Mahoenui giant wētā are fire and predators.
Fire is a huge risk in the reserve because of the danger that it could wipe out the entire original population of wētā.
Adult females are very susceptible to predation from hedgehogs, possums, rats, cats and stoats when they come down to the ground to lay eggs.
Conservation
Monitoring of wētā in the Mahoenui Giant Wētā Scientific Reserve shows numbers have declined since 2013.
However, Mahoenui giant wētā have been translocated to three sites:
- private land at Warrenheip near Cambridge
- Mahurangi Island, off the Coromandel coast – 200 were transferred there and after four years they started showing signs of breeding
- Maungatautari, a predator fenced forest near Cambridge – read about the move to Maungatautari.
These sites will be monitored to find out if Mahoenui giant wētā have successfully established a self-sustaining population. Although the sites were predator-free, they are all vulnerable to re-invasion of predators.
Future conservation plans include more translocations and a captive breeding programme.