The most common wētā are the seven species of tree wētā (genus Hemideina), found in gardens or in the bush in most regions of New Zealand (except lowland Otago and Southland).
Most adult tree wētā have bodies between 4 and 6 centimetres long. Tree wētā are predominantly herbivorous, feeding on leaves and fruit. They are seldom found alone, preferring instead to associate in groups, which often share space in tree tunnels.
By day the tightly packed gatherings are peaceful, but at night violence prevails. Male tree wētā have enlarged heads – up to twice the length of the female’s head – with oversize jaws for fighting. The larger individuals set themselves up in the best tunnels where they repel other males but accept females to accumulate a harem – five or more females where there is room. Males fight to remove lesser individuals when competing for tunnels. Fights are not to kill – although legs and antennae, or parts of them, may be lost in the process.
Tree wētā communicate by stridulation – pegs on their hind legs are scraped over comb-like ridges on the side of their body. This produces a chirping sound that they hear through ears on the sides of their front legs.
Tree wētā eggs are laid during autumn and winter, hatching in spring. The female wētā has a long, curved egg-laying spike (ovipositor), which can be bent under her body to force eggs down into the soil.
Like all insects, wētā need to shed their external covering (exoskeleton) periodically to grow. Once it has hatched from the egg, the tiny version of the adult must pass through at least 10 moults before it reaches adulthood. This process takes one to two years.
Wētā in winter
Once they reach adulthood, tree wētā survive for six to ten months in lowland situations, but in an alpine habitat they may live for several years. New Zealand alpine wētā (Hemideina maori) are by far the largest insects that can freeze solid in winter and thaw out and crawl away in spring. Most cold-tolerant insects have antifreeze (glycol) in their fluids. But these wētā can freeze because their tissues are not damaged when ice crystals form.