Giant wētā (genus Deinacrida) are predominantly herbivorous. They are not as social as tree wētā and tend to occupy temporary, poorly protected shelters by day, which exposes them to predators.
Giant wētā did not survive long in lowland areas after the arrival of humans and rats in New Zealand. Of the 11 giant wētā species, only six still occur on mainland New Zealand – in the South Island mountains, above the level where rats live. The other species now survive only on offshore islands.
The most impressive wētā is the wētāpunga (Deinacrida heteracantha), a species of giant wētā now confined to Little Barrier Island. Females reach a body length of 7.5 centimetres, and their hind legs are 13 centimetres if stretched out. Like other lowland giant wētā species, these giants of the insect world were extinct on mainland New Zealand by 1900, killed by rats.
Lawyer and naturalist Walter Buller was enthralled by the giant wētāpunga. On one occasion in the 1860s, he captured a pair in woods near the Northern Wairoa River, tying them in a knotted handkerchief which he left to pick up later. At the end of the day the wētā had gone – they had chewed their way to freedom.
The ground wētā group (genus Hemiandrus) are not as well known or studied as much as other wētā. About 30 species occur throughout New Zealand. They lack the heavily spined hind legs of the tree wētā and live in burrows in the soil, reversing into the hole so they can face any enemies head-on. These active, carnivorous wētā emerge at night to climb vegetation and hunt for insect prey. Some larger species (with bodies at least 4 centimetres in length) occur in mountain regions.
Unlike other wētā species, ground wētā do not form social groups or stridulate (chirp by rubbing body parts together).
The females of some species are known to make a special brood chamber in their burrow and care for their eggs until after they have hatched.
Mature tusked wētā males have impressive tusks for fighting. Three species occur in northern New Zealand:
- Anisoura nicobarica is only 2 centimetres long and lives in the far north, often in similar tree tunnels to the Auckland tree wētā (Hemideina thoracica).
- Motuweta riparia is about 3.5 centimetres long and lives beside streams in the ranges behind the Bay of Plenty.
- Motuweta isolata, a 6.5-centimetre giant tusked wētā, survives on a tiny island in the Mercury Islands group.
The cave wētā group is the most diverse. There are over 50 species ranging from small bush wētā only a few centimetres long to some Gymnoplectron species that have leg spans of up to 40 centimetres (with bodies only about 2.5 centimetres long).
They can be distinguished from other types of wētā by their antennae, which virtually touch in the middle of the head, and by their feet, which lack gripping pads. Cave wētā do not form harems like tree wētā, but they often gather (sometimes in large numbers if there is space) in dark, damp shelters by day. At night they forage in the bush, feeding on lichens, fungi and dead organic matter, including seabird carcasses.