.png){kind=logo}
A mountain-dwelling giant that somehow ended up living at lake level — and survives winter by freezing solid.
The mountain stone weta is normally a creature of the high country, found in rocky alpine terrain at 1,000 to 1,500 metres above sea level. Mou Waho's population breaks that rule entirely, thriving at just 300 to 475 metres — practically lake level by comparison. The best guess for how they got there is that a few weta 'rafted' across on floating logs at some point in the past, and the population simply took hold and grew. The only other place this species survives at such a low altitude is neighbouring Mou Tapu Island.
Up to 82 percent of its body water can freeze solid — the highest known figure for any invertebrate on Earth.
Adult mountain stone weta grow up to 60 millimetres long and weigh as much as 10 grams — roughly the size of a small mouse. They're nocturnal, spending daylight hours hidden in rock crevices, tree holes, rotten logs, and thick vegetation before emerging after dark to forage on a mixed diet of plant material, small invertebrates, and decaying matter. Males carry noticeably larger jaws and heads than females, using them to fight off rivals and defend a harem of up to seven females through the mating season, which falls just before winter sets in.
Surviving a cold, dry alpine winter takes some serious adaptation, and the mountain stone weta has one of the strangest going: it can freeze solid. Over the coldest months, this weta can survive being frozen at temperatures down to -10°C for up to 17 days at a stretch. The trick lies in its haemolymph — the insect equivalent of blood — which contains an amino acid that stops ice crystals from rupturing its cells as they form. Up to 82 percent of its body water can freeze without killing it, the highest tolerance recorded for any invertebrate in the world. They also lose less water through their outer shell and while breathing than lowland weta species, which helps them cope with the dry alpine air even before winter arrives.
Mou Waho's predator-free status protects its birds, but not its weta — the buff weka introduced to the island in 2004 will happily eat one given the chance. A weta's main defence is to play dead: flipping onto its back with legs splayed and claws and jaws exposed. If that fails, it can bite or regurgitate to buy itself a moment to escape. On the guided walk, look out for the 'weta motels' guides point to along the track — safe refuges built to give the island's weta somewhere secure to shelter during the day.
Ask your guide about the weta motels on our full-day lake tour, which stops at Mou Waho.
